Kookaburra: king of the bush

KOOKABURRA King of the Bush SARAH LEGGE © Sarah Legge 2004 All rights reserved. Except under the conditions describe...

Author: Sarah Legge

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KOOKABURRA King of the Bush

SARAH LEGGE

© Sarah Legge 2004 All rights reserved. Except under the conditions described in the Australian Copyright Act 1968 and subsequent amendments, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, duplicating or otherwise, without the prior permission of the copyright owner. Contact CSIRO PUBLISHING for all permission requests. National Library of Australia Cataloguing-in-Publication entry Legge, Sarah. Kookaburra: king of the bush. ISBN 0 643 09063 0 (paperback). ISBN 0 643 09137 8 (e-book). 1. Kookaburra – Australia. I. Title. (Series : Australian natural history series). 598.780994

Available from CSIRO PUBLISHING 150 Oxford Street (PO Box 1139) Collingwood VIC 3066 Australia Telephone: Local call: Fax: Email: Web site:

+61 3 9662 7666 1300 788 000 (Australia only) +61 3 9662 7555 [email protected] www.publish.csiro.au

Front cover Laughing Kookaburras perched Peter Marsack, Lochman Transparancies Back cover Laughing Kookaburras at nest David Hollands, Wildfilm Set in 10.5/14 Sabon Cover and text design by James Kelly Printed in Australia by Ligare

Contents

Preface

v

Acknowledgements

vii

1

The culture of kookaburras

1

2

Taxonomy and distribution

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3

Appearance and habits

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Social and mating system

5

Breeding

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The helping system

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Life in the nest

8

Mortality

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Conservation and management

References

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Preface Who is unaware of the kookaburra? Its fame stretches far beyond the shores of Australia. Overstuffed and cuddly mementoes adorn the shelves of visitors from as far afield as Europe and Japan. Americans walk through their malls wearing T-shirts emblazoned with its laughing face. Its image is used in all sorts of advertising, logos, and brand names for things as diverse as camping equipment and sports teams. How did the kookaburra achieve this glitterati status? Chapter 1 gives a brief outline of the chronology of its rising fame, and how indigenous Australians and more recent settlers have viewed the kookaburra. As with all figures loved and fêted by media, marketers and adoring fans, the superficial image of the kookaburra is so shiny and perfected that many people never pause to wonder what lies beneath this painted surface. The remainder of the book digs gradually deeper and deeper into the kookaburra’s natural history, as well as embellishing and explaining the background to some facts that people may already know (such as kookaburras live in groups). But have you ever wondered why they live in groups, how groups form, when and why birds decide to leave their groups, and what happens to them when they do? Who gets to breed in these groups, and what is the effect of group living on their breeding success and behaviour? The end point of these ever-more microscopic enquiries is a thorough description of what happens in the nest, and it makes for front-page tabloid material: intense rivalry for resources, murder of relatives, and Machiavellian tactics by parents to control the violent tendencies of their young. These strategies include precise control over the sex of the chicks. The book finishes with a summary of their conservation status, and management issues. Kookaburras have fared relatively well in the face of the massive habitat and ecological disruptions brought about since European colonisation. Unfortunately, many other species are not doing so well and some are at risk of disappearing altogether. Unless we radically change our attitudes to how we ‘develop’, manage and protect our land, we risk missing the chance to uncover the fascinating secrets of their natural histories, and losing the rare and rich gifts of Australia’s natural world.

ge Leg ah Sar

Acknowledgements I would like to thank Nick Alexander from CSIRO Publishing and John Elliot from UNSW Press for being encouraging and helpful throughout; their editorial comments and general guidance are much appreciated. I would also like to particularly thank Penny Olsen, who gave me all sorts of advice and encouragement. It was very comforting to have such a brilliant ‘pro’ close at hand. I received comments on various drafts of the manuscript from Nick Perkins, Daniel Ebert, Steve Murphy, and especially Chris Boland, who read the entire book. When tracking down photos and useful illustrations, the staff of the National Library of Australia were very accommodating, especially Marika Tolgyesi from the Pictures Reading Room. Also helpful were Bronwyn Dowdall from Screensound Australia, William Ernest Waites (Aboriginals: Art of the First Person), Christine Thomas (RAAF), Steve Prigg and Chris Appleton (Army), Gary Kinkade (DNRM), Greg McDonald (Pocketguide to Australian Coins and Banknotes), Terry Chesser (Australian National Wildlife Collection, CSIRO) and David Curl. The marketing logos in Chapter 1 were taken, with permission, from Mimmo Cozzolino’s book, Symbols of Australia. Thanks to Andrew Iwaniuk, who produced the figure of a kookaburra brain and contributed the text on brain structure. Mike Double, Rob Heinsohn, Daniel Ebert and Sharon Downes all allowed me to use their best kooka photos. Thanks to Peter Marsack for agreeing to let me reproduce his wonderful scratchboard artwork of an adult feeding two fledglings, and to Steve Murphy for creating some tricky illustrations for me. Graeme Chapman, Brian Coates, David Curl, Geoff Dabb, David Hollands (Wildfilm), Peter Marsack (Lochman Transparencies), Ian Montgomery (Birdway), Russell Smith (Nature Focus), Steve Stephenson, and Klaus Uhlenhut sent me photographs for inclusion in the book. Finally, Katie, Stuart and Neal at the Photographics Services (ANU), Jim Forge and Bob Phillips at the School of Botany and Zoology (ANU) helped me sort out various image copying and storage dramas. I would like to acknowledge the substantial contributions to kookaburra lore made by Keith Hindwood, an inspiring naturalist, Veronica Parry, an insightful observer of nature, Anjeli Nathan, who loved life and all the wild things in it, and David Curl, who took on the Blue-winged Kookaburras and produced a gorgeous film of them as well as his thesis. A large amount of the information presented in this book comes from my PhD research on Laughing Kookaburras, which I carried out at the School of

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Kookaburra: king of the bush

Botany and Zoology at the Australian National University. This was, and continues to be, a wonderful place in which to work. I am grateful for the support and encouragement of Rob Heinsohn in particular. I also want to thank Andrew Cockburn for his backing and academic inspiration. And while it’s still true that there are relatively few women in science, I happen to be surrounded by some remarkable women with a deep interest in the natural world. Although they have very different ways of satisfying that interest, what they have in common is a drive to grab hold of their passion with enthusiasm, and do something worthwhile with it. They are all good friends and inspiring role models: Penny Olsen, Wendy Cooper, Trish Pontynen, Sharon Downes, Janet Gardner, Cathryn Abbott, Caroline Blackmore, Tess Brickhill, and Marj Andrews. I wrote this book during a difficult time in my life, and sometimes the writing only continued because other people held bits of me together, perhaps without realising it. Janet, Karen, Mike, Penny, Chris, Daniel and Andy gave me support, perspective and wisdom; Caroline lent me some guts on top. My guardian angels Nick and Rachel materialised from nowhere and gave me a home when I needed it most; I can’t ever thank them enough. I am grateful for the shimmering soul and honest friendship of Swanie; I can’t think about him without smiling. Above all I am lucky for the hope, laughter, faith and loyalty of Steve. Even when things seemed most out of control, my parents Charles and Trees, and my brothers, Karl and John, were always steadfastly there. I hope they enjoy this book.

1 The culture of kookaburras

L

aughing kookaburras are the largest kingfishers in the world, and Bluewinged kookaburras are not far behind. Their size and distinctive shape and posture make them easily recognisable; their comical and personable characters make them readily memorable. They are able to live in a wide variety of habitats, and adapt to living around humans relatively well. This cheerful familiarity has caused them to figure prominently in the psyches and folklores of all peoples who have inhabited Australia. Two features of the kookaburra’s general biology have been particularly emphasised across cultures. First, their vocalisations are loud, intrusive and unmistakable, and have been interwoven into stories and common names. Second, all Australian peoples have recognised, fêted and overestimated the kookaburra’s ability to kill snakes. This chapter describes how these two features of the kookaburra were perceived by indigenous Australians as well as the country’s more recent settlers.

Aboriginals and kookaburras Many Aboriginal legends explain the origin or key features of an animal’s ecology, especially if the animal is important to them in some way. The most obtrusive feature about a kookaburra (from a human standpoint) is its incredible vocalisation, and most Aboriginal stories focus on the association between the kookaburra’s cacophonic dawn chorus and the arrival of the sun each day.

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The common thread in these stories is that during the early stages of the Dreaming the Earth existed in a kind of hazy twilight or even in darkness. After a while, proper days and nights were created. In some stories this was a decision taken by a Creator being. In other cases this change resulted from the events of yet another story: the sun was a giant, but unlit, woodpile in the sky. During a quarrel between Emu and Eagle (Eagle is sometimes substituted for another bird such as the Brolga), Eagle threw one of Emu’s eggs into the sky, where it struck the giant woodpile and set it alight, causing the first day of light and warmth. The spirits of the sky were so pleased by the effects that they decided to collect fuel for the woodpile every night, and light it again each morning. Unfortunately, many animals were sleeping through the daily lighting of the woodpile, which meant they had only a portion of the day left for their work, and they were also missing out on the spectacular display of dawn. The spirits commissioned Kookaburra to call just before dawn each morning, so that all the other animals would know when to wake up. There are alternative Aboriginal stories concerning the kookaburra’s call, that emphasise its mocking quality. For example the following story comes from the Bidjigal clan, between Sydney and Wollongong. In the Dreamtime, Kookaburra was a serious bird, critical of other birds that did not follow her sober example. In particular, she singled out Cuckoo for censure, because of her habit of laying her eggs in the nests of others, thereby avoiding the responsibilities of parenthood. One day, however, Kookaburra was watching Cuckoo lay her egg in Eagle’s nest when Eagle arrived back and caught Cuckoo in the act. Furious, Eagle killed and ate Cuckoo. Kookaburra broke into uncontrollable laughter at Cuckoo’s misfortune, and to this day still laughs wildly at the mishaps of others. Stories from other Aboriginal groups mirror this derisive theme, like of the Ngiyaampaa people (western NSW), where kookaburras broke into laughter when two little boys were inadvertently flattened by an enraged river goanna that they had been tickling. The Noongahburrah people (from the Narran River, NSW) have a story that tells how Goorgah, the iguana, went hunting with his two wives Moondai (possum) and Cookooburrah. They left Cookooburrah’s two young sons at the camp without water. While they were away, Cookooburrah’s older son visited the camp. When he found his younger brothers half-dead with thirst, he punished his parents by breaking open a goolahgool, which is a hollow tree that holds much water. The water flowed like a big, gushing stream. When Goorgah and his wives returned, they tried to cross the stream to reach their camp. Cookooburrah lost her footing, and called out to her little sons: ‘Goug gour gah gah. Goug gour gah gah. Give me


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a stick.’ Her sons only answered derisively: ‘Goug gour gah gah. Goug gour gah gah.’ Cookooburrah, Goorgah and Moondai all drowned. The snake-killing potential of kookaburras is celebrated in another fable from the Bidjigal clan. In this story the Kookaburra and Snake were once close friends, but one day Snake ate some of Kookaburra’s eggs. The tell-tale bulges in Snake’s body gave the sorry tale away. In retaliation, Kookaburra killed Snake and ate him, and has treated all snakes the same ever since.

Recent immigrants and kookaburras Early settlers to Australia arrived in the southeast, and therefore made the acquaintance of the Laughing Kookaburra before the Blue-winged Kookaburra. This has resulted in a greater variety of vernacular names for the Laughing Kookaburra. Settlers quickly noted the same association between daybreak and the Laughing Kookaburra’s cackling chorus as indigenous Australians, and came up with common names that were a reference to this predictable timing: ‘Alarm Bird’, ‘Breakfast Bird’, ‘Settler’s Clock’ and ‘Bushman’s Clock’. George Cayley (quoted in Gould) had a theory for the settler’s fixation with timekeeping in relation to kookaburras: ‘I have also heard it called the Hawkesbury Clock (clocks being at the period of my residence scarce articles in the colony, there being not one, perhaps, in the whole Hawkesbury settlement), for it is among the first of the feathered tribes which announce the approach of day.’

Other common names were also a tribute to the remarkable call, such as ‘Laughing Jackass’ (and its derivatives ‘Laughing Jack’, ‘Laughing Johnny’, etc.) and the name ‘Laughing Kookaburra’ itself. The term Laughing Jackass probably persisted most widely, and by 1871 it had been incorporated into ‘The Young Australian’s Alphabet’: J is for jackass A very strange bird, Whose laugh in the forest Is very absurd. Another name, the ‘Ha Ha Pigeon’, is an interesting acknowledgement of both the kookaburra’s call, and also its edibility, since pigeons were thought to be an especially delectable type of bird. Some early accounts refer to the ‘Great Brown Kingfisher’ or the ‘Giant Kingfisher’, which of course is a reference to the Laughing Kookaburra’s taxonomic affinities rather than its call. Like the Laughing Kookaburra, the Blue-winged Kookaburra also has loud, ringing, and utterly unmistakable calls. However, they have a more barking,

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chopping quality, and this is reflected in their common names: the ‘Barking’ or ‘Howling Jackass’. Other common names allude to their taxonomy or are more descriptive, like ‘Leach’s Kingfisher’, and ‘Fawn-breasted Kingfisher’. The current popular generic name, ‘kookaburra’, is derived from the Wiradhuri language, which was spoken by people living inland of Sydney and the Blue Mountains, roughly between Mudgee and Hay, Gilgandra and Albury. The word only came into common usage by settlers in 1867, after Blaxland, Lawson and Wentworth had breached the Blue Mountains in 1813. Although there may have been as many as 40 variations of the name spoken by different Aboriginal groups, most kept the basic onomatopoeic quality, and were recognised and reported in various settlers’ accounts. Different sources cite the original Wiradhuri name as being ‘cocopara’, ‘cucuburra’, ‘gogera’, ‘gogobera’, ‘guguburra’, or ‘kukuburra’. The Aboriginals of Botany Bay reputedly used the name ‘cuck’unda’, and names from other language groups include ‘akkaburra’, ‘arrangangg’, ‘gugurrgaagaa’, ‘gurgara’, ‘karkungoon’, ‘koaka’, ‘ngungana’, ‘tarakook’ and ‘wowook’. Language names that specifically refer to the Blue-winged Kookaburra are similarly onomatopoeic and therefore perhaps more staccato, for example ‘garrwukgarrwuk’, ‘garramben’, ‘orrolmb’, and ‘konkon’. The kookaburra’s wild and unfamiliar calls were not always favourably received by early settlers: ‘…appalling as the ravings of a madman…and ends in a prolonged sardonic chuckle’. Captain Sturt (related by Gould) thought the kookaburra’s calls resembled ‘a chorus of wild spirits’, and that they were ‘apt to startle the traveller who may be in jeopardy, as if laughing and mocking at his misfortune’. This perception of a sarcastic quality in the kookaburra’s call echoes the flavour of some of the Aboriginal tales related above. Other early writers with a more sympathetic ear, such as W.F. Morrison in 1888, emphasised the larrikin aspect of the calls: ‘…a most hideous exhibition of the vocal organs…reminds one very much of the braying of an ass. When many of them are together they provoke laughter by the ridiculous tones they make in concert, ludicrous in the extreme, and contagious in effect.’

Once settlers got used to these ‘ravings’, they began noticing other attributes of the kookaburra, in particular (and like indigenous Australians) its snake-killing ability. For example, in 1872 C.H. Eden wrote: ‘At daylight came a hideous chorus of fiendish laughter, as if the infernal regions had been broken loose – this was the song of another feathered innocent, the laughing jackass – not half a bad sort of fellow when you come to know him, for he kills snakes…’

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Source: National Library of Australia. nla.pic-an1133159


‘The Snake Destroyer, the Laughing Jackass’. Print from a wood engraving published in an illustrated Sydney newspaper, c. 1878.

This sentiment is seconded in another description, this time by C. Lumholtz in 1890: ‘Few birds of Australia have pleased me as much as this curious laughing jackass, though it is both clumsy and unattractive in colour…It boldly attacks venomous snakes and large lizards, and is consequently the friend of the colonist.’

The perception of kookaburras as ‘valiant snake-killers’ persisted strongly throughout the 20th century, as shown by the numerous comments and articles describing snake-eating incidents in Australia’s oldest ornithological journal Emu. Indeed, its reputation as a snake-killer was the justification seized upon by acclimatisation societies when introducing Laughing Kookaburras at the turn of the 20th century to several areas where they did not occur naturally, such as



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Startling images like this photo, published during the Marylebone Cricket Club tour of Australia in 1936/37, cemented the kookaburra’s reputation as a snake-killer.

Western Australia and Tasmania (see Chapter 2). These introductions were ironic, because although kookaburras, given the opportunity, do eat snakes, in general snakes form only a very small part of their diet (see Chapter 3). The kookaburra’s ‘vermin-destroying’ abilities did not completely inure it from criticism. Accounts show that some regarded the Laughing Kookaburra as a ‘laughing demon’ (D. MacDonald, Argus 1919), ‘A Bird of Evil’ and ‘a blood-thirsty bully’ (Prof. Osborne, Argus 13 Nov 1926) which threatened the survival of other birds. While arguing in defence of the kookaburra, D. Dickinson wrote in the Emu during 1927: ‘The status of the kookaburra has been much discussed in Victoria of recent years, owing to its alleged habit of pilfering nests containing young birds. Those who are opposed to this bird being kept on the protected list contend that there is no greater evil amongst the smaller forms of bird-life than the Laughing Jackass.’


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This move to throw kookaburras off the protected list was thankfully fought off by more sensible amateur and professional naturalists. Like snakes, young birds make up a very small proportion of a kookaburra’s diet (see Chapter 3). The perception of them as small-bird killers has persisted most strongly in Tasmania, possibly because Laughing Kookaburras are recent exotics, and residents were (and remain) worried about the effects of this on their native fauna. In spite of this hiccup to its image in Tasmania and Western Australia, the kookaburra’s popularity blossomed enormously in the first few decades of the 1900s, due to several factors. Aside from its legendary snake-killing potential, and its reputation as a jovial, good ‘sort of fellow’, the kookaburra had become a favoured subject in the work of some prominent artists, notably Neville Cayley (1853–1903). It became a common image on a range of postcards intended for sending to distant relatives and friends overseas. During the First World War, the kookaburra and the wattle were the two most heavily used themes on postcards sent to the boys in the trenches to boost their morale and remind them of home. These images were often accompanied by rhymes such as The Kookaburras’ Evening Song by Les H. Pritchard: Oh! My heart, how it yearns for Australia, It holds all that is dearest to me, The wild bush and vast plains of Australia, Is what I am longing to see. The great gum-trees and fair golden wattle, With its fragrance so rare and strong, To hear after a hard day with cattle, The Kookaburras’ Evening Song.

The kookaburra became a symbol of nationalism during wartimes and was incorporated into the badges of several military units. Source: Mimmo Cozzolino, Symbols of Australia, RAAF and Australian Army.


Source: Australian War Memorial. Ref. No. 008625

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Source: Australian War Memorial. Ref. No. 085625

The Australian Division’s kookaburra sign displayed on the mudguard of Major General Allen’s car, which brought the Vichy representatives into the Allied lines.

Sergeant J. Hawkins at the Herberton Racecourse, Wondecla, Atherton Tableland, in January 1945. The young kookaburra on his shoulder had pecked him just before the picture was taken, hence the expression.

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Indeed, in wartime the kookaburra became a potent symbol of Australian nationalism, donning military regalia to emerge as ‘Diggaburra’. By the Second World War, the kookaburra had become incorporated into the badges of several military units of land, air and sea (see illustration, page 7). The kookaburra was used in various formation signs, as a mascot (see opposite), and it was even used as the name of a ship, the HMAS A trial square penny minted Kookaburra, commissioned in 1939. As well as its position in military nationalism, during 1919–1921. the kookaburra achieved iconic triumphs in the civic sphere. In 1914 it was used to decorate the third ever national stamp after Federation, and imprinted on the square-shaped penny and halfpenny coins, minted in 1919–1921 from cupro-nickel metal. These trial coins were intended to replace the heavier bronze pennies and halfpennies, and were square in order to distinguish them from the similarly coloured, higher denomination, silver coins. Unfortunately, the slot machines of the time could not cope with the square innovations, so the trial coins were soon abandoned. They are now a valuable collector’s item, with some editions being worth around $57 000. To capitalise on its spectacular popularity, many businesses began registering various depictions of the kookaburra as trademarks. For example, M. Cozzolino describes nearly 30 different trademarks that were registered between the two World Wars, for products as diverse as cigarette paper tubes,

The 1931 trademark (left) of the Kookaburra Cigarette Paper Tube Mfg Co., Sydney has to be one of the more bizarre uses of kookaburras in marketing. The Australian Knitting Mills Ltd, Melbourne registered this trademark (right) for their ‘unshrinkable’ hosiery in 1913. Source: Mimmo Cozzolino, Symbols of Australia.

Greg MacDonald


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The ‘Early Kooka’ stove, registered by Metters Ltd, Sydney around 1920. Source: Mimmo Cozzolino, Symbols of Australia.

hats, safety matches, building products and tea (the Digger Tea Supply Co. took over the wartime ‘Diggaburra’ as their trademark logo in 1922). There were two particularly clever uses of the kookaburra theme in marketing. Companies selling something that was reminiscent of a snake played upon the kookaburra’s snake-killing fame (e.g. ‘Kookaburra’ hosiery by the Australian Knitting Mills Ltd (see page 9); ‘Kookaburra’ spaghetti by Hancock’s Golden Crust Pty Ltd, Melbourne, 1928; ‘K’Burra’ whips by Walther & Stevenson, Sydney, 1922). Other companies with a kitchen connection played upon the word similarity between kooka and cooking (e.g. the ‘Early Kooka’ stove by Metters Ltd, Sydney, 1920 (see above); ‘Cookaburra’ Patty tins by Briggs Bros Pty Ltd, Melbourne, 1927.). As well as infiltrating the worlds of nationalist symbols and marketing, the kookaburra was used in children’s storybooks from the late 1800s. Who killed cockatoo? by W.A. Cawthorne around 1870, was one of the earliest children’s books to be written, published and printed in Australia. It featured several Australian animals, including the kookaburra: Then flying very fast Came Laughing Jackass Hoo hoo hoo! Ha ha ha! While he gobbled a snail And wagged his big tail Hoo hoo hoo! Ha ha ha! Like this rhyme, most stories and jingles tended to emphasise the notable characteristics of the kookaburra, as usual either its hunting abilities or its


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calling, or both, such as these verses from Grandmamma’s Verse-Book for Young Australians by L.A. Meredith, published in 1878: Three large grey birds sit up in a tree And they look as solemn as birds can be, With very big beaks, and half-shut eyes – Did you ever see anything look so wise? Hark! All on a sudden one of the three Bursts out a laughing! “Ha, ha! Ho, hee!” Why are all three of them staring so? See – there’s a black snake down below! Gliding along thro’ the dry brown grass – But not very far will he safely pass; Those solemn old birds are watching him go, And chuckle for joy – “Ha ha! Ho ho!” Down they pounce! – they have got him fast! – He writhes and twists, but that twist was his last! He meant on some poor bird to sup, But the strong big birds have eaten him up, And laugh, as they fly back again to the tree, “Ha ha! Ho ho! Ha ha! Ho hee!” The kookaburra continued to be a favourite children’s storybook character in the 20th century, used in the Snugglepot and Cuddlepie stories of May Gibbs, and as the main character in several other stories, including Jack Sundowner by F.J. Mills in the 1930s, where the kookaburra assumes the persona of the wandering, carefree swagman. The 20th century also saw the birth of the most famous kookaburra jingle of all, the chorus of which is familiar to children and adults from all corners of the world: Kookaburra sits in the old gum tree, Merry merry king of the bush is he, Laugh kookaburra, laugh kookaburra, Gay your life must be. Kookaburra sits in the old gum tree Eating all the gum drops he can see, Hey Kookaburra, wait Kookaburra Leave some there for me.

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Kookaburra sits in the old gum tree With a toothache bad as can be, Ha Kookaburra, ha Kookaburra Didn’t leave any for me. Marion Sinclair wrote the song in the 1930s, and designed it to be sung in rounds. It may have been sung first at a Girl Guide Jamboree in Victoria, but from there it conquered the world. As well as the original verses, there have been some amusing variations on the theme: Kookaburra sits on the electric wire Tears in his eyes and his pants on fire Ouch Kookaburra, Ouch Kookaburra Hot your tail must be.

Jacko – an avian superstar One of the most (if not the most) famous individual birds in the world was a Laughing Kookaburra, called Jacko, who died in 1939 at Healesville, at the ripe old age of fifteen. He had lived with the Jury family, and was apparently quite a character. In the evenings, while perched by the fire with the Juries, he would often fall asleep and lapse into gurgling, chortling kookaburra dreams. He also taught a family of puppies to howl and wail as a background chorus to his own set piece at dusk each day. His fame grew out of his ability to break into wild kookaburra laughter on command. This made him a valuable asset to some radio stations that had been using kookaburra calls as the opening or closing signature to their programs since the 1920s. Over the years, recordings from about five different kookaburras have been used on radio, and also as background sounds denoting exotic (but inappropriate) places like African jungles in Tarzan films. But the most widely used recordings came from Jacko, played on dozens of local radio stations as well as Radio Australia’s overseas service. Jacko’s career extended beyond radio: he cut a gramophone record, made many stage appearances along Australia’s East coast during a lecture tour by the naturalist Dr Brooke Nicholls, and became a film star, performing first in an Australian ‘short’ and then in the openings to the Fox Movietone newsreels. His adventures were immortalised in a fictionalised biography (Jacko – the Broadcasting Kookaburra) written by Dr Nicholls and illustrated by Dorothy Wall, in 1933. Jacko made one particularly interesting broadcasting appearance on Melbourne’s Radio 3LO, together with Miss Hazel Maude, aka ‘Little Miss Kookaburra’, who hosted a daily children’s program. Little Miss Kookaburra was able to deliver a remarkably realistic impersonation of a kookaburra call,

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Source: Screensound Australia


A still from the Fox Movietone Newsreel opening sequence.

and on the day of Jacko’s visit to the Radio station, they actually performed a duet. In Jacko’s own words: ‘After I had done my solo we put over a duet. I started first. When [Miss Kookaburra] joined in I stopped short and looked at her. It was the first time I had heard a human laugh really like a kookaburra. Then I joined in again and laughed my hardest. We cackled and gurgled and chuckled together. Our voices blended perfectly. If Miss Kookaburra had not been a really good mimic, I would not have joined in with her. I once heard a lyrebird broadcast his imitation of my laugh. I took no notice of it.’

As well as illustrating Jacko’s biography, Dorothy Wall also wrote the children’s classic Blinky Bill, first published in 1939. By this stage, Jacko was so familiar to the public that she was able to integrate his character into the story – Jacko was Blinky Bill’s godfather. Mr Koala contacted Jacko through the bush wireless, and arranged a date for the christening to fit around Jacko’s busy broadcasting schedule. In some ways, the zenith of kookaburra-mania has dimmed as it now has to share the limelight with other animals that have become equally well loved and well marketed, like the koala, wombat, and goanna. However it remains

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an instantly recognisable icon of Australiana both nationally and internationally. For example, a web search using a popular search engine for the word ‘kookaburra’ revealed over 61 000 ‘hits’. By way of comparison, other iconic birds such as the sulphur-crested cockatoo resulted in about 6600 hits, fairywren in about 4900 hits, and cassowary had about 22 000 hits. The kookaburra’s place in our popular culture seems assured for some time yet.

The Laughing Kookaburra, as depicted by Sarah Stone, circa 1790.

2 Taxonomy and distribution

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he Laughing Kookaburra was one of the earliest Australian animals to be described by European scientists. Its arrival into the annals of the scientific world is an interesting story that reveals much about the politics and ambition of natural history collectors at the time. Pierre Sonnerat, a French naturalist, is credited with collecting the first specimen of the Laughing Kookaburra around 1770. After returning to France he had the skin illustrated by Daubenton; this plate was printed in Sonnerat’s 1776 book Voyage à la nouvelle Guinée. The legend to the plate reads ‘Grand martin-pêcheur de la nouvelle-Guinée’ (‘Big Kingfisher from New Guinea’). He also claimed to have observed the bird (as well as another kingfisher) in the forest there. On the surface this account of the collection seems reasonable, but he slipped up on two points: first, Laughing Kookaburras do not occur anywhere on the mainland or satellite islands of New Guinea. Second, the ship he was travelling on never made it east of the Moluccas, Indonesia. History has shown that Sonnerat’s ambition sometimes drove him to be economical or even inventive with the truth, and the Laughing Kookaburra’s introduction to the scientific world seems to be a case in point. In reality, Sonnerat was probably given the skin by Joseph Banks when Sonnerat’s ship met Cook’s Endeavour at the Cape of Good Hope in 1770, on its return voyage from the Antipodes. The ‘kookaburra scandal’ as well as other, similar indiscretions by Sonnerat (such as stealing some penguin skins from his

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colleague Commerson’s collection and passing them off as New Guinean birds) were overlooked by the authorities because he had been involved in an enormous French economic triumph – the Dutch spice monopoly was finally broken by a small group of Frenchmen (including Sonnerat) who smuggled some valuable plants away from the spice islands. Although it was collected just before or during 1770, the Laughing Kookaburra was not given its scientific name until 1783. Nevertheless it was still only the second bird from Australia to be properly classified. In fact, two taxonomists set to work on it simultaneously, using Daubenton’s plate and Sonnerat’s inventive observations. Boddaert called the bird Alcedo gigas (‘big kingfisher’), and Hermann named it Dacelo nova Guineae (‘New Guinean kingfisher’). Hermann’s work was generally less well known than that of Boddaert, and for over a century the kookaburra was known as Alcedo gigas. However, in 1900 Hermann’s work was unearthed by Richmond, who suggested it had precedence over Boddaert. The vexing problem of the Laughing Kookaburra’s correct scientific name was taken up later by others such as Streseman in 1920, Matthews in 1926, and most notably Lysaght in the 1950s, who continued to push the case that Hermann had published marginally before Boddaert. They prevailed, and the taxonomic rule of priority means that Sonnerat’s story of plagiarism and deception is quaintly immortalised in the Laughing Kookaburra’s scientific name, Dacelo novaeguineae. A close examination of an annotated list of Banks’s collection shows that he actually collected a specimen of the Blue-winged Kookaburra on the same voyage that he collected the Laughing Kookaburra. However, he held on to this specimen rather than giving it away to Sonnerat. When Latham used Banks’ annotated list to briefly describe the ‘Great Brown Kingfisher’ in his 1782 book A General Synopsis of Birds, he amalgamated plumage features that are, in reality, unique to only one of the two kookaburras. He described the bird as having a dark eyestripe (which is unique to the Laughing Kookaburra) and also commented on a bright-blue rump, tail and wing coverts (which applies to the Blue-winged Kookaburra). This ‘coalescent’ bird was later officially described by Gmelin in 1788, and named Alcedo fusca. However, that name had to be dropped for the Blue-winged Kookaburra since Boddaert had already used it for another species of kingfisher five years previously. Eventually, in 1827 Vigors and Horsfield furnished a description and name, Dacelo leachii, which has proven to be relatively problem free. They based their description on a specimen collected in 1802 at Keppel Bay by Mr Brown, who sailed on the Investigator during Matthew Flinders’ circumnavigation of Australia. Beginning with this voyage, Brown, a protégé of Banks, made a profound contribution to botanical knowledge in Australia. Ferdinand

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Source: National Library of Australia. GMM 919.5.SON


The first European depiction of a Laughing Kookaburra, by Daubenton and published in 1776 in Voyage à la nouvelle Guinée by Pierre Sonnerat. The drawing was based on Sonnerat’s specimen and descriptive notes.

Bauer, the expedition’s artist, made some sketches of the Blue-winged Kookaburra that may be the first European representation of this bird. The specific name, leachii, honours the contribution to zoology by William Elford Leach, a doctor and curator at the British Museum between 1813 and 1821. On the subject of names, the scientific name for the genus that includes all kookaburras, Dacelo, has an interesting etymology in itself. Dacelo is an anagram of Alcedo, another genus of kingfishers. Alcedo is derived from the Greek work for kingfisher – ‘halcyon’ (hals, salt or the sea, and kuo, to brood on, or conceiving). In Greek legend, Alcyone, the daughter of Aeolus (God of the Storm-Winds), tried to drown herself when she found the body of her love Ceyx, the king of Thessaly, washed up on the beach after a winter storm. (Incidentally, Ceyx is the name given to yet another genus of kingfishers.) In a

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merciful mood, Zeus transformed them both into kingfishers. The kingfishers mated and then nested on the stormy seas. In order to protect his future grandchildren, Aeolus calmed the winds while Alcyone and Ceyx tended the eggs. The Greeks believed that kingfishers always laid their eggs in floating nests out on the sea, during the calm interlude around the winter solstice that interrupted the normal winter storms. This led to the description ‘halcyon days’ for calm weather in the middle of winter. The legend became a much-favoured allegorical tool of poets such as William Shenstone (1714–1763): There came the halcyon, whom the sea obeys, When she her nest upon the water lays

The Coraciiformes: kookaburras and their relatives The bird order Coraciiformes contains birds, like kookaburras, with a heavy head and bill, short neck, short legs and toes, weak feet, and three forwardpointing toes that are joined for part of their length. Their plumage is usually bright (the Laughing Kookaburra is one of the dullest species). They all nest in cavities and lay smooth, pure white eggs. Coraciiform chicks hatch blind and naked, and grow feathers that remain encased in sheaths right up until fledging; since conditions in a nest hole get rather rancid, this may be an adaptation to protect the growing feathers from being fouled. There are three major lineages of kingfisher: the Halcyonidae, Alcedinidae, and the Cerylidae (see schematic tree opposite). Although they are instantly recognisable as kingfishers, these three groups diverged and radiated long enough ago to elevate them to the status of families. Within the Coraciiformes, the closest relatives to the kingfisher families are the motmots and todies, which live in the Neotropics and Caribbean, then the bee-eaters, and finally and more distantly, the rollers, ground-rollers and cuckoo-roller. Debate exists about the exact relationships between the three kingfisher families. One possible scenario is that the Halcyonidae (which contain the kookaburras) are the ancestral kingfisher group. They are also the most easily recognised family, and are still mainly found where they originally radiated – in the tropical forests of northern Australasia, including New Guinea and its satellite islands. Their foraging technique tends to be relatively unspecialised compared to the other two kingfisher families – with a few exceptions, they are generalised predators of invertebrates and small vertebrates, often using a sit-and-wait strategy. Although the early halcyonids were forest-dwellers, some forms expanded out into drier and more open habitats (like the Laughing and Blue-winged Kookaburras themselves). About 40 million years ago the alcedinids arose and radiated in south and


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south-east Asia. Some developed a specialised foraging technique – fishing – and this enabled them to colonise watercourses and pools far from the dense forests. At some point about 5–10 million years ago an alcedinid crossed the Bering Strait to start a radiation in the Americas; these became the cerylids, which are also specialised fishers. As a short aside, the umbrella term ‘kingfisher’ for the halcyonids, alcenidids and cerylids is really a misnomer, because less than one third of all kingfisher species (around 90, depending on the classification) actually fish for a living (i.e. the cerylids and the genus Alcedo in the alcedinids). Most kingfishers hunt terrestrial prey, and they can live far from water, like the red-backed kingfisher, Todiramphus pyrrhopygia, which lives in arid parts of Australia. However, the only kingfisher that inhabits western Europe (the river kingfisher, Alcedo atthis) is a spectacular fisher. Since the fledgling science of zoological taxonomy in the 1700 and 1800s was very Euro-centric, the somewhat inappropriate name ‘kingfisher’ was extended to cover the whole group. A better umbrella term might have been ‘dagger-bill’, ‘bush-dart’, or perhaps ‘bush-jewel’.

FAMILIES Coraciidae (rollers) Brachypteraciidae (ground-rollers) Leptosomidae (cuckoo-roller) Momotidae (motmots) Todidae (todies) Halcyonidae (tree kingfishers, including sacred and forest kingfishers, and kookaburras) Alcedinidae (small blue and rufous kingfishers, including the azure and little kingfishers ) Cerylidae (green and giant kingfishers, mainly American) Meropidae (bee-eaters)

Schematic tree showing the relationships between groups within the Coraciiformes.

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Kookaburras worldwide There are four species of kookaburra, all in the genus Dacelo. The Laughing Kookaburra, D. novaeguineae, is endemic to Australia, the Blue-winged Kookaburra, D. leachii, occurs in the south of New Guinea as well as north-east, northern and north-western Australia (Figure 2.2). The remaining two species are exclusively New Guinean: the Spangled Kookaburra, D. tyro, is found in Aru Islands and the savannah of southern New Guinea, while the Rufous-bellied Kookaburra, D. gaudichaud, inhabits lowland rainforests throughout the mainland and some outlying islands (Figure 2.1) (see pages 26 and 27). All kookaburra species are large sit-and-wait predators. They are sedentary, territorial, and have ear-splittingly distinctive calls. The Rufous-bellied Kookaburra is perhaps the most unusual species in the group: it lives in forests and other dense vegetation, whereas the other three kookaburras are mainly birds of woodlands. The Rufous-bellied Kookaburra is also pair-dwelling, unlike the Laughing and Blue-winged Kookaburras which live in social groups where all or most adults help raise the young of the breeding pair. The social system of the Spangled Kookaburra is unknown; it has never been studied and its nests have rarely been found.

The Australian Kookaburras Laughing Kookaburras are found in suitable habitat in a broad band from the tip of Cape York in Queensland down the east coast of Australia to the Eyre Peninsula of South Australia. They extend furthest inland where rivers and drainage channels are large enough to support trees with hollows. Vagrants occasionally turn up west of the normal distribution. In the past 100 years deliberate introductions have seen its range expanded to include the southwest corner of Western Australia, Tasmania, and some smaller islands. The Laughing Kookaburra is spilt into two subspecies, mainly on the basis of a difference in size. The nominate subspecies, D. n. novaeguineae, occupies most of the species’ range, between South Australia and the base of Cape York Peninsula. The smaller subspecies, D. n. minor, is restricted to Cape York Peninsula (Figure 2.2). There are some indications that details of natural history may vary between the subspecies, for instance the clutch size may be larger in D. n. minor. Although the distributions of these two subspecies are contiguous, there appears to be a sharp disjunction in morphology at the boundary. It would be interesting to verify this, and investigate how and why the disjunction is maintained. The Blue-winged Kookaburra is a relatively northerly bird compared with the Laughing Kookaburra, distributed in a broad swathe from Brisbane, up the east coast to Cape York Peninsula, across the Northern Territory and


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Figure 2.1 The Rufous-bellied Kookaburra occurs in the lowland rainforests of New Guinea and the Aru Islands (light and dark shading). The Spangled Kookaburra occupies a more restricted range, in the southern part of New Guinea and the Aru Islands (dark shading).

Figure 2.2 The Laughing Kookaburra, D. novaeguineae, is endemic to Australia; the Bluewinged Kookaburra, D. leachii, occurs in the south of New Guinea as well as north-east, northern and north-western Australia.

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south-west to Carnarvon in Western Australia, albeit with a break between Broome and Port Hedland. The distributions of the Laughing and Blue-winged Kookaburras overlap in Queensland. When they occupy the same area, kookaburras usually defend their territories from individuals of the other species as well as their own. Taxonomists disagree as to whether and how the Blue-winged Kookaburra should be divided at the subspecific level. Some taxonomists suggest there is only a single subspecies in Australia, based on the continuous distribution of the species and the fact that differences in size and plumage may exist as a gradual geographical cline. The most widely accepted current classification describes four subspecies: the nominate race D. l. leachii occurs throughout most of the range, between Brisbane to Broome; D. l. cervina occurs on Melville Island and a narrow coastal strip on the mainland opposite (where it intergrades with D. l. leachii), and D. l. cliftoni (sometimes called D. l. occidentalis) occurs in the Hammersly and Pilbara Region of Western Australia. Finally, New Guinea has its own subspecies, D. l. intermedia (Figure 2.2).

Kookaburra habitat

Sarah Legge

If asked to describe where a kookaburra lives, many people would answer: ‘eucalypt woodlands’. Indeed, the quintessential kookaburra image is a relaxed bird squatting solidly on a low branch, head askance and craned to the ground, peering through air hazy with the blue fumes of gum resin. However, while it is true that kookaburras make an excellent living in open woodlands,

A typical kookaburra woodland habitat.


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they are certainly not restricted to this habitat type. Kookaburras are sedentary and territorial all year round; their territories therefore need to include everything required for nesting as well as foraging in all seasons. Although they prefer areas without thick ground cover to facilitate hunting, the only essential ingredient required for successful occupancy is a potential nesting site – either naturally occurring tree hollows or arboreal termite mounds. Any treed habitat, from semi-arid areas to dense forests, including rainforests, are therefore open to occupation, although the density of birds can be very low in these less optimal areas. They also cope with areas that have been cleared by humans, such as farmland, parklands and suburbia, as long as at least one hollow-bearing tree stands nearby and there are handy perching aids (like telephone wires or fences) from which they can sit and hunt.

Introductions In the late 1800s and early 1900s, acclimatisation societies sprang up all over Europe and its colonies. Private individuals had dabbled with experimental introductions of exotic plants and animals to other countries for some time, but these societies institutionalised and evangelised the process. The acclimatisation societies of Australia and New Zealand were particularly zealous, introducing many species of mammals and birds to their local areas. Although most of these failed to establish self-sustaining wild populations, we have been left with the dubious legacy of some notable exceptions, such as the introductions of sparrows, starlings, and foxes. The Laughing Kookaburra was a popular subject for transportation, thanks to its personable nature and its reputation as a useful predator of vermin. During a lecture to the Society of Arts in 1860, Frank Buckland, an enthusiastic exponent of the Acclimatisation Society of the UK when it was still in its fledgling stage, justified a possible introduction of the Laughing Kookaburra to the UK because ‘it is excessively adroit in catching mice, and will wait as patiently as a cat at a hole whence he expects one to emerge!’ Similarly, in an 1875 report by the Acclimatisation Society of Victoria to the Foreign and Colonial Office in the UK, ‘Laughing Jackasses’ were recommended ‘as most desirable additions to British Parks’ because of their ‘merit, as vermin-destroying animals’ and because of the ‘robust, jovial humour of their merry pleasant notes and quaint manners’. Although the motions to introduce kookaburras to the UK were never passed by officialdom, some individuals apparently did bring back isolated specimens. Gould noted that one bird lived for several years in the Gardens of the Zoological Society of London, and that in the 1840s a Mr Yaldwyn had brought a single Laughing Kookaburra from NSW back to his country seat in Sussex.

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Around 30 Laughing Kookaburras were introduced to both the North and South Islands of New Zealand between the 1860s and late 1870s, by private individuals as well as the Otago, Canterbury, Auckland, Nelson and Wellington Acclimatisation Societies. These efforts were mostly unsuccessful, but a small population still clings on in the Hauraki Gulf, and birds are sometimes seen near Whangarei. Around the cusp of the 19th and 20th centuries, Laughing Kookaburras were also introduced to Fiji, but they disappeared from there within 25 years. The most successful transportations of the Laughing Kookaburra did not involve long ocean voyages; they were introduced to parts of Australia where they did not naturally occur: Western Australia, Tasmania, and Flinders, Kangaroo and Waterhouse Islands. Laughing Kookaburras were probably first introduced to Western Australia in 1896 by private individuals, but beginning in 1897, the Western Australian Acclimatisation Society released several hundred kookaburras around Perth and the south-west, purportedly to kill tiger snakes, which were predicted ‘to increase with the top dressing of the pastures and become a real nuisance’ (EA Le Soeuf, Director of the Zoological Gardens, Perth; in CFH Jenkins 1977). Although it is unlikely the snake populations suffered any dints, the kookaburras took off dramatically, breeding in the first year following their release. Currently they cover the whole of the south-west corner of Western Australia. The Launceston Acclimatisation Society and private individuals began releasing kookaburras on the north coast of Tasmania and Waterhouse Island around the same time, from 1902 onwards. The fate of the birds was followed with great interest by locals: ‘the Laughing Jackasses which were liberated…some time back have nested and have two young ones flying about with them’ (Anon; 1903). In 1907 Miss Fletcher reported in the Emu: ‘It is with feelings of greatest pleasure that I record that several pairs of (kookaburras) are quite at home in the district, and are evidently the progeny of a pair that was liberated at BelleVue.’

Kookaburras are now established over most of Tasmania. In 1926 two pairs of Laughing Kookaburras were released on Kangaroo Island, and after a hesitant start, they are now well established there. Finally, kookaburras were introduced to Flinders Island around 1940, although they may have colonised from nearby Waterhouse Island even earlier. In their efforts to improve the environment, acclimatisation societies never touted the Blue-winged Kookaburras as a suitable émigré. This was probably because fewer people were familiar with the bird, rather than any significant differences in the snake-killing potential or ‘amusing characters’ of the two species.

Dacelo cervina from John Gould’s Birds of Australia.


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Source: National Library of Australia. SRef 598.2994 9 697


David Hollands

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David Hollands

The Blue-winged Kookaburra, Dacelo leachii, occurs in the south of New Guinea as well as north-east, northern and north-western Australia.

The Laughing Kookaburra, Dacelo novaeguineae, is endemic to eastern Australia.

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Brian Coates


William Peckover

The Rufous-bellied Kookaburra, Dacelo gaudichaud, inhabits lowland rainforest throughout New Guinea.

The Spangled Kookaburra, Dacelo tyro, is found in the Aru Islands and the savannah of southern New Guinea.


Sarah Legge

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Female Laughing Kookaburras tend to have brown rumps, while males tend to have blue rumps. However, this is not always consistent: the brown-rumped bird on the left is actually a male. Specimens housed at the Australian National Wildlife Collection.

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Sarah Legge


The female (left) and the male (right) Blue-winged Kookaburra have differently coloured tail feathers. Specimens housed at the Australian National Wildlife Collection.


Source: National Library of Australia. nla-pic an 684 3376

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An albino kookaburra, painted by Neville Cayley in 1890.

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Klaus Uhlenhut


A Blue-winged Kookaburra focussing intently on its prey.


Mike Double

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Mike Double

The head feathers of a fledgling Laughing Kookaburra (above) are darker than those of an adult (below).


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Mke Double

With hindsight, many of the activities of acclimatisation societies seem at best rather fanciful and at worst like ecological suicide. Where do the Laughing Kookaburra introductions stand on that continuum? Although it is safe to say that kookaburras have never reached the extremely destructive potential of foxes or cats, we have no idea what impact they have had in places like Western Australia and Tasmania on prey species or other animals which use similar food and tree hollow resources. Because of its status as an introduced animal, the kookaburra is currently listed as ‘vermin’ in Tasmania; it therefore has no legal protection and can be killed on sight. There are no data available to show if this is warranted from a wildlife management perspective; if kookaburras have minimal impact, then resources are probably better spent tackling more pressing environmental concerns. Nor do we know whether the introductions achieved their original objectives. For example, are tiger snake numbers around Perth lower than pre-introduction times? Are the spirits of Hobartians lifted by hearing the kookaburra’s jovial and hilarious calls each day? Either way, the populations of kookaburras in Western Australia and Tasmania are large and entrenched enough that it would prove difficult to eradicate them.

Kookaburras adapt better than many birds to human habitat modification. For example, they learn to use powerlines and fence lines as vantage points for hunting.

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History of field studies on kookaburras Following the taxonomic descriptions of the kookaburras, scientific enquiry in the form of field observations comprised short but numerous anecdotal notes on breeding times and sites, clutch sizes, feeding and predation events, mostly presented in the Emu. Such reports were relatively more common for the Laughing Kookaburra than the Blue-winged Kookaburra, as the former’s distribution brought it into contact with people more frequently. Keith Hindwood, one of Australia’s most talented naturalists, made some of the first thorough observations of the Laughing Kookaburra in the 1940s. Veronica Parry took natural history research on wild kookaburras a step further while studying the social and breeding biology of Laughing Kookaburras in the Dandenongs in Victoria. This research was for her Master’s degree (1968), based out of Monash University. She was one of the first ornithologists in the world to colour-band birds in her study population, and this individual recognition gave her greater insights into their social lives than ever before. More recently, major advances in molecular technology (allowing accurate assignment of parentage, and genetic identification of an individual’s sex) and optic technology (miniature surveillance cameras that can be mounted inside nest hollows) have allowed myself and Anjeli Nathan to probe the secret lives of kookaburras even further. Parry described the range of kookaburra vocalisations in detail, but a more sophisticated sound analysis and exploration of their function was carried out by Heinz-Ulrich Reyer and Dieter Schmidl, and more recently by Myron Baker. David Curl undertook the first (and so far, the only) systematic study of the breeding biology and behaviour of the Blue-winged Kookaburra; the results of this research are presented in his doctoral thesis (Monash University, 1999). Studies on the physiology and anatomy of kookaburras are relatively few, but have focused on interesting and sometimes unique features, such as their exceptional vision (a trait shared with other species of kingfisher, and extremely valuable for an ambush predator; M. Moroney and J. Pettigrew), their slow metabolic rate (useful for a bird that spends most of its day sitting quietly; Bill Buttemer and colleagues), and their brain structure (Andrew Iwaniuk).

3 Appearance and habits

T

he size of the Laughing Kookaburra, at 310 to 360 g, rather than its colour, makes it an eye-catching animal. Indeed, it is one of the dullestcoloured kingfishers worldwide; its plumage is mostly a combination of browns and dirty whites. However, they are by no means nondescript. As with many other kinds of ‘brown bird’, closer inspection reveals exquisite and subtle shading, barring and colour toning of siennas, umbers, and greys on each feather. Some individuals have a striking blue patch on each wing and on the rump. The brown stripe through the eye is very distinctive, and its size and shape varies considerably between individuals, as shown on the next page. The shape of the eyestripe is maintained between moults, and consequently can be used for individual identification once the researcher has become accustomed to noting them. Moreover, birds from the same group often have similar eyestripes to other group-members, suggesting the eyestripe shape is heritable. It is a widely held misconception that the sex of a Laughing Kookaburra can be identified by the amount of blue feathering on the rump, with brownrumped birds being female, and blue-rumped birds male. Since I have personally witnessed blue-rumped ‘males’ laying eggs, this myth should most definitely be laid to rest. But more conclusively, we are now able to identify the sex of a bird by examining its DNA after taking a tiny blood sample, and this has unambiguously shown that although females usually have brown rumps,


Sarah Legge

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Heads of two Laughing Kookaburras (top and middle) showing differences in eyestripes. The Blue-winged Kookaburra (bottom) lacks the distinctive eyestripe, and has a white rather than a brown iris.


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and males usually have blue rumps, there are far too many exceptions to use rump colour as a diagnostic feature. The only caveat is that if a bird has an extremely bright blue rump, then it probably is a male (see page 28). Plumage can be used, to a limited extent, to age Laughing Kookaburras. Young birds usually fledge with fine but relatively dense barring on the white feathers of their head, chest and belly (see page 32). From far away this gives the bird a dirty or ‘muddy’ look. In most birds, this barring gradually fades in the first year or two of their life, but once again, there is so much variation in the plumage of adult birds that one can not confidently use this character as a method for aging individuals. In contrast, a physical character that is reliable is the colour of the lower beak. A fledgling begins its life outside the nest with an all-black beak; over the next few months the lower beak takes on the characteristic bone colour seen in adults. However, the gormless behaviour and incessant begging of a youngster during these months usually give its age away, without needing to resort to the appearance of its beak or its plumage. Blue-winged Kookaburras are slightly smaller (260 to 330 g) than Laughing Kookaburras, but because they have a similar shape and outline the two species are often confused. However, their plumages are quite different. Most notably, Blue-winged Kookaburras lack the Laughing Kookaburra’s signature eyestripe, instead having (at most) a streaky grey ‘shadow’ where the eyestripe should be. The brown eye of the Laughing Kookaburra is replaced by a white iris. Coupled with the relatively more massive beak, it is this peculiar face that gives the Blue-winged Kookaburra its manic, steely-gazed appearance (see illustration opposite). Blue-winged Kookaburras also have a gorgeous patch of iridescent blue on their wings and rump, much larger and showier than their congener. Unlike Laughing Kookaburras, the sex of Blue-winged Kookaburras is easily recognised in the field, because males have blue tails while females’ are brown (see page 29). Aging is also more reliable, as young birds have a brown iris that fades to the piercing white in the first two years of life. There are occasional reports of melanistic or albino kookaburras; sometimes the latter are not true albinos as their irises are brown rather than white. Albino kookaburras have been observed and recognised for some time, since they are represented in some of the earliest depictions of kookaburras, such as one by Cayley shown on page 30, from 1890.

Habits Kookaburras start their day early. First call of business is usually a throaty session of group chorusing. Often this takes place well before dawn, perhaps so that birds can capitalise on premium foraging times between night and early

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morning, when nocturnal prey is still about, and diurnal prey is just getting going. Their foraging tends to tail off towards the middle of the day, when they might spend a few hours preening and loafing in the shade. Hunting resumes later in the afternoon and peaks again just before dusk. Although birds forage alone, they are often fairly close to other group members with whom they maintain contact using sporadic and various calls. Episodes of group territorial defence can crop up at any time. Groups are most cohesive leading up to and during breeding. Once the young are independent, kookaburras become quieter and less conspicuous, particularly when they moult their feathers between April and June. The birds in a kookaburra group roost together, or perhaps occasionally in two or more subgroups. They gather at one of a few favoured roost trees shortly before, during, or just after dusk. This is the point at which they often break into their group chorus, and again in the mornings before they leave the roost tree.

Foraging habits Unlike other predators that either chase prey or optimistically fossick for goodies, kookaburras are classic ‘sit-and-wait’ predators. It would be misleading to describe the foraging style of kookaburras as active. Instead, they sit immobile on a branch, and let their eyes do the hunting. In fact, they spend the majority of their time motionless apart from the occasional head movement or a languid episode of feather-ruffling. This slow-paced foraging style may be linked to an unusual metabolic physiology. Bill Buttemer has shown that Laughing Kookaburras have a lower body temperature (1–1.5ºC less) and basal metabolic rate (about 14% less) than expected for a bird of its size. At night the Laughing Kookaburra goes into a ‘mini shutdown’, where its temperature drops 2.6ºC, and its metabolic rate is only about two-thirds of the predicted level given the ambient temperature. They are also extremely well insulated, losing 18% less heat through their feathers than one would expect. This may be useful for a relatively sedentary bird that generates less heat from muscle activity than other bird species. A kookaburra searches the ground for prey by peering keenly, regularly cocking its head from side to side (see page 31). There is a good reason for the characteristic sideways peering. Like all kingfishers, kookaburras have extraordinary eyesight. In each eye, light can be focused onto one of two fovea (areas of high cone cell density), instead of the single fovea in each eye that humans have. One fovea focuses light from a cone of light in front of the bird. The cones of light, or fields of vision, from the right and left eyes partly overlap, and the binocular vision enables good distance perception. This is analo-


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Klaus Uhlenhut

gous to our own vision. The second fovea in each eye focuses a cone of light from the side of the bird; the fields of vision for each eye therefore do not overlap, such ‘monocular’ vision is poorer for estimating the distance to an object. However, the monocular fovea have a greater density of specialised retinal cells than the binocular fovea, which give them greater acuity and make them much better at picking up movement. This explains why kookaburras use just one cock-eye to search for their prey. Once the prey is located, another visual adaptation comes into play. In each eye, the monocular fovea projects in a plane that points relatively more downward that the forward-pointing binocular fovea. In effect the kookaburra sees a circle on the ground below where all the points are equidistant, rather than a linear block where points at the sides would be further away than points directly in front. This means that the image of the prey can be transferred from the monocular to the binocular fovea quickly and smoothly without the risk of losing the prey item when the head is turned. Once this is done, the prey then lies in the overlapping fields of vision of the two front-facing binocular fovea, allowing better distance-perception. By this stage, the hapless prey has little chance.

Laughing Kookaburras spend most of their time sitting fluffed-up and motionless on a branch.

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Once the kookaburra locates its delicacy, it swoops down upon the reward in a graceful dive, landing next to the prey then stabbing down simultaneously with its beak to capture its food. Kookaburras, like all kingfishers but unlike many other carnivorous birds such as raptors, have rather weak, ineffectual feet, and therefore they always use their beak to grasp their prey. If successful in the hunt, kookaburras often fly up to a perch to swallow the morsel whole. If the prey is too large or awkward to swallow immediately, they systematically ‘tenderise’ it by bashing it repeatedly against the branch while moving it gradually in little gulps sideways through their beak (see pages 70 and 71). Kookaburras have a pronounced bony ridge at the back of their skull, giving a large area for attachment of the neck and head muscles that facilitate this powerful beating action. Once the prey is pulverised, it is quickly swallowed, and the bird then usually wipes its beak repeatedly against a branch, presum-

Figure 3.1 Kookaburras (like many other birds) have two fovea in each eye. One fovea, which focuses light from the side of the bird, has very high acuity. Once a prey item is located, the kookaburra can turn its head vertically around an axis to transfer the image onto the forward-facing fovea. The kookaburra can now focus on the prey with both eyes; this binocular vision gives enhanced distance perception, so the kookaburra can gauge the distance of its pounce flight accurately. Illustration by Steve Murphy, adapted from Moroney and Pettigrew (1987).


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ably to clear debris off the sides of the bill. Indigestible material is often regurgitated as pellets; these can sometimes be seen under favourite perches. Andrew Iwaniuk has discovered that both the kookaburra’s heavy beak musculature and its visual adaptations are reflected in its brain structure. The kookaburra brain is flattened dorsoventrally, resulting in a brain that is wider than it is long. Similar flattening is also present in Tawny Frogmouths (Podargus strigoides) and hawks, eagles and falcons, but the kookaburra brain is by far the widest for its length. This is undoubtedly related to the large jaw muscles encircling the back of the brain case. The area of the brain that relates predominantly to vision in animals is the Wulst. It receives projections indirectly from the optic nerves and processes movement, colour and three-dimensional images. The Wulst is delineated on the surface of the brain by a prominent valley or sulcus that runs along either side of it. In species with binocular vision akin to humans, such as owls, the Wulst is the dominant feature of the telencephalon. The telencephalon or forebrain is the ‘thinking’ part of the brain where information from the senses is processed and integrated, action commands are delivered to muscles and decisions are made. Species with poor binocular vision, such as waterfowl, possess a much smaller Wulst that is less clearly defined on the surface of the brain. In other species, such as falcons and kookaburras, the Wulst is still clearly delineated, but is not the dominant feature of the telencephalon. This is expected, because the Laughing Kookaburra (and also Sacred Kingfisher, Todiramphus sanctus) have similar visual optics to some Figure 3.2 The brain of a subadult Laughing Kookaburra from the side, top and bottom. The areas indicated on each figure are as follows: CB – cerebellum, M – medulla, OB – olfactory bulbs, ON – optic nerve, OT – optic tectum and W – Wulst. Source: Andrew Iwaniuk.

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diurnal raptors and they share similar foraging and prey capture behaviours. Thus, the brains of kookaburras and diurnal raptors have convergently evolved a similar brain structure in response to their reliance upon visual stimuli when foraging from a perch. In terms of its other structural elements, the olfactory bulbs are relatively small, but not as small as that of passerines and parrots, nor as large as seabirds or waterfowl. Like the shape of the brain, the olfactory bulbs are similar in size to the raptors. In fact, many aspects of the kookaburra brain are convergent with that of diurnal raptors. They all share relatively large motor coordination (cerebellum) and visual centres (optic tectum), but a medium to small-sized telencephalon. Overall, kookaburras, like the coraciiforms in general, possess averagesized brains compared to all other birds (4.31 ml and 4.28 ml for the Laughing and Blue-winged Kookaburras respectively). However, within the order Coraciiformes, the kookaburras possess slightly larger brains than predicted by body mass alone. The only coraciiforms with larger brains relative to the kookaburra are the todies of South America. It is tempting to think this might be something to do with their complex social structure, but group living is prevalent in several other coraciiform groups with relatively smaller brains, particularly the bee-eaters, so there is probably no connection.

Diet Kookaburras are generalist hunters of animals living on or near the ground – they will eat anything that they feel able to swallow. The relative proportions of different types of prey in the diet reflect the frequencies with which those items occur in the kookaburra’s territory. As such, all studies that have quantified their diet (either from examining stomach contents or from observing adults feeding young) have found that arthropods (insects, spiders, millipedes, etc.) and small reptiles (mainly skinks) make up the vast majority of the menu. These are, after all, the most common small animals scurrying over a woodland or forest floor. Depending on the location, other types of prey such as annelids (worms), molluscs (snails), crustaceans (crabs and crayfish), frogs and fish are sometimes taken to varying extents. More rarely, kookaburras dine on adult and nestling birds, small mammals and snakes. Some of the rarer types of prey are the most startling to the average human observer, and this explains the large number of anecdotal reports in the birdwatching literature describing kookaburras using anvils to break open snails, attacking yabbies, birds, small mammals and especially snakes. The vivid sight of a kookaburra gamely struggling to subdue and swallow a snake (especially poisonous copperheads, tiger snakes and red-bellied black snakes) probably


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contributed to their popularity with ophidiophobic early settlers. Indeed, many of the earliest paintings of kookaburras show them grappling with a snake (see page 25). Some of the rare prey items that are eaten by kookaburras border on the bizarre. One example is the Giant Gippsland Earthworm (Megascolides australis), which is endemic to South Gippsland in Victoria and reaches up to 2 m in length. In a survey of local landowners that was designed to collect distributional records of the worm, one common way that respondents came across the worm was because they saw it being eaten by a Laughing Kookaburra! Predation by kookaburras on these ludicrously oversized prey is surely a case of their eyes overwhelming their stomach, and sometimes kookaburras paid a small price for their gluttony: ‘My attention was drawn to a kookaburra sitting on the road. I thought it had been injured and stopped with the idea of moving it off the road. I noticed that it had about 4 inches of the large worm protruding from its beak and obviously would not be able to fly for some time… It was 36 hours later before the bird was able to fly…it appeared to be in some sort of stupor; maybe just from being overfed… (A. Stubington, in Victorian Naturalist, 1982)

Likewise, on another occasion:

Sharon Downes

‘During the ploughing, quite a number of the worms would get sliced by the plough. It used to be a real bonanza for the kookaburras as they used to tug and pull at the severed pieces of the worms. It was rather amusing

Kookaburras will hunt anything they feel able to swallow whole, and some things they clearly cannot.

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at times to watch these birds when they flew to a nearby tree trailing a 2–3 ft. length of worm. Sometimes the worm would get snagged on a branch and they would swing to and fro on the length of the worm trying to dislodge it.’ (M. Hillberg, in Victorian Naturalist, 1982)

Since they live in such diverse habitats, kookaburras probably need to be able to adapt to variation in the available prey base; this may explain why they are accomplished opportunists. They rarely miss a chance to avoid the labour involved in ‘normal’ hunting, as many picnickers who have had to guard their sausages on the barbeque from marauding jackasses will attest to. Given time, wild kookaburras can become very tame and learn to eat food offered by humans. Occasionally this causes health problems, particularly to growing chicks, if the diet becomes unbalanced or lacks critical nutrients. Apart from capitalising on scraps offered by humans, kookaburras are not generally scavengers; they are unlikely to be seen at a carcass. However there are unusual reports of them learning to take advantage of situations that result in animal mortalities. For example, Blue-winged Kookaburras may use fire fronts in the same way as black kites, to mop up insects that have died or are escaping from the flames. In another example, the following excerpt from an article in the Emu by A. Mattingley in 1902 contains an interesting observation about some opportunistic Laughing Kookaburras: ‘Recently while watching a Sparrow-shooting match at Oakleigh I observed a pair of Laughing Jackasses…repeatedly fly down from a neighbouring tree and carry off the mortally wounded Sparrows within 25 yards of the shooters. In all they demolished nine Sparrows. I was informed that directly the Jackasses hear the shooting they fly over to the shooting ground and wait for their prey.’

Finally, to conclude this section on diet, there are a small number of reports that suggest kookaburras occasionally descend to kleptoparasitism (stealing food from other animals). For example, a pair of Laughing Kookaburras was once seen attacking a hawk, apparently to steal the snake the latter was carrying. In another incident, D. O’Grady (Australian Birdwatcher 1961) observed a Laughing Kookaburra harassing a snake: ‘Suddenly, the kookaburra flew down and struck at the snake…and then it flew on to a nearby fence. The bird had a large green frog in its bill, which it had apparently taken from the mouth of the snake, and it commenced to smash the frog against the rail of the fence. The snake raised its head…before disappearing into the undergrowth.’


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It is possible that these events were misinterpreted by the observers. The pair of kookaburras may have attacked the hawk because it was a potential predator (and then later capitalised on the dropped prey item), and similarly, the kookaburra that attacked the snake may have perceived the snake as prey initially, but then settled for a regurgitated frog following the mêlée. Nevertheless, if it does occur, kleptoparasitism by kookaburras is certainly very rare.

Territoriality Both species of kookaburra are sedentary, living in group territories which they defend all year round from other kookaburras. Consequently, their territory has to contain all the necessary ingredients for a happy and fulfilling kookaburra life – potential nesting hollows, roosting trees, and food through all the seasons. Different types of habitat contain different amounts of these resources, and this explains why the density of kookaburras varies so dramatically between places. For example, estimates of the densities of Laughing Kookaburras can be as high as one bird per 1.25–1.3 ha in the Dandenongs and near Armidale. But in open woodland near Canberra one kookaburra occupied an average of 25 ha, and it is likely that in more arid areas the density of birds would be even lower. Blue-winged Kookaburras show similar variation, with densities ranging from one bird per 1.4 ha to one bird per 33 ha in the Northern Territory. Kookaburras go to great lengths to defend their territories. The two species use very similar tactics, which can be divided into three approaches. First, they advertise their claim to neighbouring groups with cacophonic chorusing, especially at dawn and dusk, when all or most of the group coordinate to create a bedlam of noise. Laughing Kookaburras produce loud chortles, growls and cackling laughter; Blue-winged Kookaburras produce sounds more akin to barks and hiccups. Their choruses are unmistakable but rather hard to describe, causing verbal descriptions to rely on evocative rather than onomatopoeic phrases like ‘demoniacal laughter’. The group chorus probably conveys much information to other listening kookaburras. A study of Laughing Kookaburras by Reyer and Schmidl in the 1980s near Armidale found that the duration and loudness of the chorus increased with the size of the group. Large groups also tended to call earlier in the mornings, and later in the evenings. These features offer information about the size of the group to neighbours. More recently, a study of the same species by Mike Baker in Western Australia showed that the choruses of different groups were acoustically distinct from each other. In other words each group has a unique vocal ‘signature’ which could be used by other groups to

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recognise the identity of the calling group. How this signature arises is unclear. Kookaburra vocalisations are made up of several syllables that can be put together in different proportions and sequences, perhaps analogous to an accent. The simplest explanation for a group-specific signature is that each individual has its own accent, and when you combine individuals into a group chorus it will tend to sound different, by chance, from that of another group which is made up of different individuals. Alternatively, if accents have a genetic basis and are heritable, then young kookaburras will tend to sound similar to their parents, and this could generate differences in the sound of group choruses. Another intriguing possibility is that young kookaburras may ‘learn’ their combination of syllables from their parents, and thus conform to the accent of their group. This would be remarkable, as unlike the majority of songbirds, non-passerines (e.g. kingfishers, parrots, waterfowl and hornbills) are believed to have very little (or even no) capacity to learn their vocalisations. The second approach used by kookaburras to defend their territory is the performance of highly ritualised displays, again directed towards neighbours. Unlike chorusing, which can occur out of sight or sound of another group, ‘border displays’ always involve some or all members of two groups lined up on either side of a narrow ‘disputed’ zone that marks their shared boundary. Amidst much enthusiastic calling, the two groups perform two types of flight display. In one type of display (called the ‘circle flight’ by Veronica Parry), a single bird from one group flies up over the trees and crosses into the rival group’s territory, making a wide circle and then returning to its own territory. As it returns home, a bird from the rival group takes off and makes its own incursive circle behind enemy lines. Groups often take polite alternate turns at these flights for several minutes. In the second type of display (‘belly-flop display’ or ‘trapeze flight’), a single bird flies from its perch to another tree 5–20 m away in a graceful swoop that ends with a flared landing on the lip of a hollow. It pauses there momentarily, then swoops back to its original perch. Often no hollow is available, and the displaying bird gives the impression of ‘belly-flopping’ against the tree-trunk before pushing off for the return journey. On the return flight it usually passes another bird from its group doing exactly the same thing. The two birds pass each other as though they are trapeze artists. The performing birds are watched intently by the rest of their group. After one or more belly-flops, the performers may pause to allow the neighbours to mount their own display. As with circle flights, groups may have a session of alternating belly-flop displays that carry on for some time. The third defensive approach, unlike the two described above, is neither ritualised, polite, nor non-contact. It is used against single birds found intrud-


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ing deep into the territory. These singletons, far from their own groups, are prospecting for breeding vacancies and dispersal opportunities. If discovered by the territory owners they are immediately attacked, often without any vocal warnings. The attacks can result in injury, and are sustained until the intruder is seen off over the territory boundary. All three defensive approaches peak in frequency in the two or three months preceding the breeding season. This is the period when birds that hope to find breeding vacancies in another group skulk around prior to permanent dispersal. This is also the time when neighbouring groups reaffirm the position of shared borders. The frequency of group chorusing (or in Blue-winged Kookaburras the duration of a chorus bout) also peaks just after nestlings leave the nest – a period of high group cohesion and excitement, so this behaviour may serve some group-bonding functions as well as defence.

Figure 3.3 Ritualised displays. In the ‘circle display’ (top) birds trace a circular path over the heads of a neighbouring group. The neighbouring group does the same in reverse, so the resulting pattern can seem like a figure-ofeight. (The inset shows the flightpath from above.) In the ‘belly-flop display’ (bottom) birds from the same group take turns at flying between a perch and a hollow or a scar on a nearby tree. Illustration: Sarah Legge


Sarah Legge

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Singleton intruders are seen off the territory promptly and aggressively.

Territory size increases with group size – this has been shown in one study of Blue-winged Kookaburras, and three separate studies on Laughing Kookaburras in different places. Although an obvious conclusion is that larger groups have larger territories because they are better able to defend them, this may not necessarily be the case. In both Laughing Kookaburras around Canberra, and Blue-winged Kookaburras in Kakadu, the territory size of each group and the position of shared borders appeared to change very little between years. In fact, territories appeared to be traditional. Moreover, groups tended to stay the same size – simple pairs tended to remain as pairs between years, or perhaps to swell briefly to three then deflate again. Similarly, large groups tended to remain large. This presents a ‘chicken-and-egg’ situation. Does the group size determine the territory size, or is the size of the group limited by the size of the territory owned by that group? I believe the latter is at least partly true, based on two different pieces of evidence. In my study of Laughing Kookaburras around Canberra there were a few cases where a large group reduced dramatically in size between years because of mass-dispersal of grown offspring (e.g. from 7–8 to 2–3 birds) but the territory borders remained unchanged, suggesting it was not the presence of extra helpers per se that caused the group territory to be large. Second, simple pairs (i.e. where the group size is two) produced more daughters than sons in their broods. If the territory does impose a ‘cap’ on the group size, then this is a ‘sensible’ strategy because females are more likely to disperse before they reach one year than males, and therefore impose less of a drain on the territory resources (see Chapter 4). Conversely, if these small groups ‘wanted’ to increase in size they should have produced sons, yet they did not. So it seems that parents tailored the sex ratio of their offspring to match their territory.

4 Social and mating system

K

ookaburras are cooperative breeders. This is an umbrella term for breeding systems where some birds (the so-called ‘helpers’) care for young that are not their own. Cooperative breeding is relatively rare in birds – various estimates suggest that it occurs in around 3–5% of all species, although this proportion can be much higher in some groups of birds. It also occurs relatively frequently in Australia compared with other biogeographic regions. Many familiar birds in Australia are cooperative breeders, for example Magpies, Fairy-wrens, Apostle Birds, White-winged Choughs, all species of babbler, Scrubwrens, some thornbills, Magpie-geese, some treecreepers…and many others. The paradigm of natural selection hinges on each individual maximising the flow of its genes to the next generation – this is the fundamental expression of that individual’s ‘fitness’. Cooperative breeding has provided a fertile field of study for evolutionary biologists during the last three decades, because superficially it seems that some individuals in these species forfeit their own breeding efforts to help the reproduction of others. This is counter-intuitive, and the challenge to evolutionary biologists has been to demonstrate whether and how these apparent exceptions actually prove the rule. In each species that has been studied in depth, it can be shown that helping behaviour is far from selfless – helpers enjoy one or more of a range of benefits

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that increase the share of their genes in the next generations. These benefits may be direct, such as mating with the breeding female in the group (sometimes surreptitiously), learning breeding skills that enhance their own reproductive efforts later in life, or inheriting the territory when their parents die or move. When the breeders that the helper assists are related, the benefits may be indirect. For example, the help might increase the reproductive success of these relatives so much that the helper’s share of genes in all the extra brothers, cousins, nephews and nieces outweighs the genes in the helper’s own offspring if it were to attempt reproduction by itself. In the last 10 years the advent of genetic techniques has allowed us to find, unambiguously, how each bird in a cooperative group is related to each other, and who are the biological parents of each batch of offspring. This has been fundamental to our understanding of cooperative breeding, as the ‘real’ mating system can be quite different to the social system inferred from observation alone. For example, Noisy Miners live in large groups and matings occur between many different birds. Although this strongly suggested that several individuals within the group shared reproduction, a genetic study has shown that the mating system is actually monogamous – the clutch is produced by only one male and one female. At the other end of the scale, Superb Fairy-wrens live in groups that contain a socially dominant pair, yet genetic analyses reveal them to have an extraordinarily complex mating system, where about three-quarters of all nestlings are fathered by a male who is not the social father. Because of the potential incongruence between the social and mating systems, genetic analyses of parentage have become essential for a proper understanding of any animal’s breeding biology. In order to identify why individuals live in groups and help rear the offspring of others, we need to document the mating system and the genetic relatedness between individuals in the group, as well as describe its social system. Of the four species of kookaburra worldwide, only the Rufous-bellied Kookaburra of the New Guinean lowland rainforests is known to be pairdwelling. The social system of the Spangled Kookaburra is unknown, but the Laughing and Blue-winged Kookaburras live in cooperatively breeding groups. The social systems of both have been studied in some detail, particularly for the Laughing Kookaburra. In the latter species, molecular genetic analyses have also been used to reveal the mating system. Since both species have very similar social systems, and the mating system of Blue-winged Kookaburras is unlikely to differ substantially from that of Laughing Kookaburras, this chapter focuses on the composition, dynamics and mating system of the Laughing Kookaburra. With this framework in place, Chapter 5 focuses on a thorough

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Sarah Legge


Laughing kookaburras can live in groups of up to nine birds; groups of three are fairly common.

description of breeding, as a lead-in to Chapter 6, which describes the helping system and its effects on breeding success. Chapter 6 finishes by integrating what we know about the social, mating and helping systems in a discussion of why kookaburras live and breed in groups.

Group size and formation Laughing Kookaburras live in pairs, or groups of three to nine birds, although some huge groups of up to 16 birds have been reported. The most common group sizes may vary between different habitats – Table 4.1 shows the distributions of group sizes from two places, the Dandenongs and Canberra. Simple pairs seem to be more common in the Dandenongs than around Canberra. Table 4.1 Distribution of group sizes at Canberra and the Dandenongs. Group Size

2 3 4 5 6 7 8

No. of groups seen in Canberra 1994–97

44 29 29 15 8 4 1

Relative proportion

34% 22% 22% 12% 6% 3% 1%

No. of groups seen in Dandenongs 1965–66

10 5 4 2 1 0 0

Relative proportion

45% 23% 18% 9% 5% 0% 0%

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Each group contains a socially monogamous pair that is dominant over the other birds – they are able to displace other group members from perches, win beak-wrestling matches (see illustration, page 61), and they call and lead choruses more than the other birds. The dominant pair usually remains together for many years, until one or both die (10 to 15 years). They also monopolise the breeding (see ‘Mating system’ below), although all group members contribute to the care of eggs and young, as described in Chapter 6. Helpers are recruited into the group from young hatched in previous years, never from other, unrelated groups. This means that a kookaburra group is made up of close relatives – often the mother, father, and helpers of various ages from different broods from previous years.

When and why do birds leave their groups? The members of a dominant pair almost never leave their group. Very rarely, a bird may ‘divorce’ its partner for a new mate on a nearby territory. In the few cases where this has been observed it was always the female who moved away, suggesting the male and the territory are a package and the female is relatively more mobile. In contrast to the dominant breeding birds, most helpers do eventually leave their natal group. They always disperse by themselves rather than in a coalition with other helpers (as White-winged Choughs do). The age at which individuals fly the coop varies widely from around ten months to five or six years, possibly more. An important factor that determines how long a youngster stays at home is its sex. Females are likely to disperse from their group at a younger age than males. In about 35 groups studied for four years around Canberra, males stayed and helped for a median of two seasons before dispersing, while females only stayed for a median of one season. About 40% of females even left their natal group towards the end of their first year before having helped at all, and no females were known to stay in their natal group after having helped for two seasons. When youngsters leave, there are no obvious signs (like fights and chasing) that their parents are evicting them, although there may be subtle behavioural cues that we, as observers, miss. Helpers almost never disperse and ‘float’ around without a territory of their own. Instead, they immediately join another group, but they only do this in order to take up a breeding vacancy as a member of the dominant pair, and never join another group in order to help. Breeding vacancies arise most commonly when an incumbent dies, and helpers from surrounding territories are instantly aware of these opportunities. Neighbours may pick up on the fact that the missing bird is no longer calling, or there may be other cues from the ‘widowed’ group like a change in territorial behaviour. Helpers from further


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afield who are keen to improve their lot in life learn about opportunities because they regularly embark on surreptitious reconnaissance trips around territories far away from their own. Rather than waiting for an incumbent breeder to die, another method for acquiring a breeding position is to find an accomplice of the opposite sex from another group and carve out a new territory by aggressively pushing the new neighbours aside. Alternatively, some new pairs manage to ‘bud off’ a territory from one of their parents’ territories. The latter technique often occurs when the two new breeders are from adjacent and therefore traditionally rival natal groups – a Romeo and Juliet situation! This budding phenomenon means that neighbouring groups are often more related to each other than to groups two or three territories away. This can be seen using DNA fingerprinting techniques that look at the genetic relatedness between individuals from neighbouring versus more distant groups (see box, page 54). When a dominant breeder dies, the vacancy is always filled from outside the group. The position is never inherited by a helper already present in the group. This may be because in the vast majority of cases the upwardly mobile helper would then be paired to a parent; kookaburras, like many other animals, probably exercise strong incest taboos to avoid the problem of inbreeding. However, other cooperatively breeding birds get around this problem by having systems where the remaining incumbent disperses, thereby bequeathing the territory to one or more of its offspring (e.g. Superb Fairywren mothers), or even by the helper(s) evicting the remaining parent and thereby creating a vacancy that they can fill. The latter scenario may occur (albeit extremely rarely) in kookaburras – when one breeder is replaced, an opposite-sexed helper very occasionally vies for the dominant position with its same–sex parent. Once a new breeder is installed in the kookaburra group, many of the helpers disperse away from the natal territory over the next year. This is probably because when they help the new step-parents they are less related to the new broods than when they were helping their full parents. The genetic fitness benefits of helping from producing half-brothers and half-sisters are less than from producing full siblings, and they are only easing the parenting burden for one (instead of both) of their own parents, so it may be more worthwhile to try and find a breeding position of their own.

Mating system As mentioned in the introductory paragraphs of this chapter, in some bird species the mating system as revealed by genetic techniques sometimes does not match that implied by the social system. However, Laughing Kookaburras

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provide a case where the social and mating systems are perfectly congruent – in a large sample of 140 nestlings from 41 different groups, the socially dominant pair was the true parents of all chicks. Mating was never shared with helpers in the group, even when the group was a step-family where any incest taboos were circumvented because a helper could mate with an unrelated step-parent. Nor was parentage ever leaked to kookaburras from outside the family group. Figure 4.1 illustrates the effect that the strict monogamy has on relatedness within and between groups. We can estimate the genetic relatedness for any pair of individuals (a dyad) by calculating the average number of ‘bands’ they share on a DNA fingerprint (see box opposite for an explanation of bands). Full relatives should share at least half of their bands, but non-relatives will share very few. If we plot a frequency histogram of the number of dyads with different categories of band-sharing, it is clear that nestlings are highly related to adult birds in their own group, but much less related to birds from other groups (Figure 4.1a). Figure 4.1b further splits the relationships within a group to nestling-mother, nestling-father, and nestling-helper. The distributions for each type of relationship all show that a high proportion of bands are shared. The distributions are also overlapping, indicating that groups are made up entirely of close relatives. In Laughing Kookaburras, the strict monogamy is surprising because some behavioural traits suggest that fertilisations by a male other than the dominant male are a real possibility. Group members of the same sex often fight in the lead-up to the breeding season, suggesting conflict over dominance and access to breeding. Even more remarkable, it is not unusual to see the female copulating with a bird that is not her partner. However, these copulations are perfunctory, they usually occur when the female is unlikely to be fertile, often after an interaction between groups or between birds within the group, and they take place in conspicuous locations like the tops of trees with the other group members voyeuristically looking on. Moreover, copulations sometimes occur between same-sex birds. All these observations suggest that in some contexts copulations have some kind of social signalling or bonding function, and are not designed to result in a fertilisation. More generally, the kookaburra’s penchant for strict monogamy seems strange because breeding females have been found to mate with males other than their social mates in many species of bird. When it occurs, the frequencies of this behaviour range from very low to startlingly high (like the Superb Fairy-wren). Females may ‘choose’ to mate with other males for many reasons, such as improving the genetic stock of her offspring, insuring against the possible infertility of her social mate, and enticing the extra-pair male to provide some parental care to her chicks.

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(a)

(b)

Figure 4.1 (a) Distribution of bandsharing values between chicks and an adult bird from another group, and chicks with an adult bird from the same group; the graph shows that chicks are much more related to adults within their own group. (b) Distribution of bandsharing values between chicks and their mothers, fathers, and helpers in their groups. The distributions are completely overlapping, indicating that even helpers in the groups are usually full relatives.

In species like kookaburras, where breeding adults live for many years and generally remain in the same group until they die, breeding vacancies crop up relatively rarely. In effect this constrains the choice of mates available to any bird looking for a breeding position. Under these circumstances, we might expect birds to accept the first breeding vacancy they can, even if their new partner leaves something to be desired, but then make secondary choices about who to actually mate with – sneakily if necessary.


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Given these mate choice constraints, and the potential genetic benefits of mating with other males, the question remains: why are kookaburra females so faithful? One possibility is that the dominant male guards her so effectively that she never gets the opportunity to quietly shop around for a better genetic investment for her offspring. In the run-up to egg laying the dominant male follows the female around diligently and is especially vigilant and intolerant towards intruders. Nevertheless, kookaburras live on large territories, and if a female really wants to shake her social mate for a short while, she probably gets the opportunity to do this. A more likely explanation is that the kookaburra female chooses to remain faithful. Her male partner is extremely valuable – he incubates the clutch during the day more than she does, and provides the bulk of food to nestlings (Chapter 6), which is a difficult task. He may do this partly because he is a better provider than the female. Unlike most birds where males are bigger than females, kookaburras are reverse size-dimorphic: females are over 13% heavier than males. This probably makes males relatively more manoeuvrable and adept at the constant back-and-forth movements required to keep a hungry brood satiated. Of course this leads to the question – why is the female larger? If a territorial male is a scarce and valuable commodity, females may compete with each other for access to this resource. At some point (presumably at 13% heavier than the male!) the advantages of being large will be balanced by its drawbacks: the larger she gets, the more difficult her own energetic budget becomes (because she needs to hunt for more food to stay alive) and the more difficult it is for her to feed young. Females experience higher mortality than males at all ages (see Chapter 8), consistent with the idea that they are larger than ‘ideal’. Determining which came first – competition between females for breeding vacancies (leading to an increase in their size relative to males and a reduction in their parental care), or a greater investment by males in the breeding effort (making him a valuable resource for which females must compete, leading to an increase in their size) is a tricky problem. But whatever the explanation, male and female kookaburras may now be locked into a social contract where the female remains faithful in return for the male’s parental care.

Implications of the social and mating system for understanding cooperative breeding The description of the social and mating system above allows us to eliminate some benefits of helping that are common in other species. Kookaburra helpers do not stay at home and help raise young so that they can inherit the territory (either by waiting for a dominant bird to die, or by evicting it). Nor,

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given the strict monogamy, do they help in order to maintain mating access to the dominant female in their own or in neighbouring groups. Finally, since they disperse as singletons, they do not stay at home in order to form alliances with other group-members so that they can disperse into other groups in a strong coalition. Among the remaining possibilities underpinning the helping system, the most obvious next line of questioning is to look at the effect of helpers on the breeding success of their parents. Since groups are composed of close (usually full) relatives, helpers could increase the breeding success of the group sufficiently so that the extra siblings compensate for their own lack of offspring. They could do this either directly, through contributing to the provisioning of nestlings, or indirectly, through bolstering territory (and thus resource) defence. In addition, when helpers provision young the breeders may be able to reduce their own workload. This could prolong the lifespan of the breeders, leading to a greater number of clutches over their lifetime, which also means ‘more siblings’ from the helper’s perspective. This topic will be dealt with in Chapter 6.

5 Breeding

T

here is a considerable amount of information available on kookaburra breeding – including a 1965–1966 study by Veronica Parry of 19 Laughing Kookaburra nests in the Dandenongs, and a more comprehensive study by myself and others in the late 1990s of more than 130 nests in the woodlands around Canberra. This chapter concentrates on the results from Canberra, bringing in Parry’s earlier observational work when there are any significant points of difference. Most information on breeding by Blue-winged Kookaburras comes from the study at Kakadu National Park by David Curl (of about 40 nests), and indicates that the breeding biology of the two species of kookaburra is very similar.

Breeding timetable In both species, the eggs take 24–26 days to hatch after being laid. The nestlings fledge after another 32–40 days. After fledging, the young still require attention and feeding for a further 6–10 weeks before they have learnt to hunt for themselves. Consequently, the entire breeding effort from egg laying to finally producing independent offspring is relatively prolonged, taking four months or more. Laughing Kookaburras breed seasonally throughout their range, usually laying their eggs in September or October. However, clutches can be laid as

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early as August, and as late as December. By and large, they only raise one brood of young in a breeding season, but occasionally females do lay a second clutch after a successful first attempt. If a breeding female loses her first clutch unexpectedly (e.g. to predation) she often has another attempt. Despite being largely tropical, Blue-winged Kookaburras breed at a similar time of year to Laughing Kookaburras, also laying most eggs in September and October. The end of their breeding season may be more sharply curtailed by the onset of heavy monsoonal rains that can flood nest hollows and drown any eggs and chicks that are still in the nest. In many species of bird, breeding appears to be timed so that nestlings and fledglings are present during the period when food is most abundant – spring in temperate latitudes and the start of the wet season in tropical areas. However, in both species of kookaburra, the onset of breeding appears to be decoupled from annual differences in climatic conditions (and thus prey biomass). For example, the four-year study around Canberra included a drought year and a year of above-average rainfall, but the laying dates in each year were the same. Similarly, Blue-winged Kookaburras at Kakadu always began laying eggs at the same time each year, despite large differences in the timing of the first heavy rains. This insensitivity to rainfall and thus invertebrate biomass may partly stem from the wide culinary tastes of kookaburras – the ability to hunt such a large variety of prey items may free them from heavy dependence on resource flushes. In addition, given the length of their nesting cycle, it may be too difficult to accurately predict when the food resources will reach their peak.

Behaviour in the pre-breeding period Kookaburras spend a lot of their time sitting quietly and motionless on a branch, and this can make them fairly inconspicuous. However, in the month or two leading up to egg laying, kookaburras are anything but inconspicuous, as they get involved in various noisy and flamboyant displays. The frequency of territorial proclamations and physical disputes increases dramatically, and the position of territory borders can change at this time. The proclamations— raucous group vocalisations similar to the familiar dawn and dusk chorus— can be made from anywhere in the territory, but are more common near the borders; the ‘opposition’ need not be present. The physical disputes usually occur between neighbouring groups on either side of their border, and involve the highly ritualised circle flight displays, belly-flopping and calling described in Chapter 3. During the pre-breeding season the incidence of intruders also increases – singleton birds skulk carefully through established territories, presumably looking for breeding vacancies. If spotted, they are immediately

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Sarah Legge

Breeding

Kookaburras from the same group fight by locking their beaks and twisting, trying to force each other off the branch.

attacked without ceremony and chased out of the territory. This furious reaction by the rightful residents contains no sign of the ritualised display behaviour characteristic of neighbourly interactions. The behaviour of kookaburras towards fellow group-members also alters during the pre-breeding period. Normally fairly sedate and composed, the intensity of social interactions increases with individuals becoming both more irritable as well as more attentive towards each other. Birds of the same sex fight more frequently, locking bills while perched together on a branch and twisting with their heads until one (usually the younger, subordinate bird) is forced off the perch. Group-members tend to stay closer to each other, and maintain contact with regular, soft, gurgling calls. The dominant male and female become especially close, rarely being out of each other’s sight, contactcalling regularly, and often instigating loud chorus calls or responding to a similar instigation by their partner. This ‘closeness’ probably serves a reciprocal mate-guarding function – the male can make sure his mate does not solicit attention from rival males, while the female can assure herself of her mate’s complete and unwavering devotion. The dominant female is regularly fed by her mate, and more sporadically by other group members. As well as being part of courtship, this ‘allofeeding’ may have an important nutritional role for the breeding female, helping her sequester resources while she is forming eggs. In particular, it may free her

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from having to forage for herself when she is actually laying the clutch, leaving her more time to spend at her nest guarding the egg(s) and beginning incubation. Copulations occur fairly frequently during the pre-breeding period, even though the dominant female is very unlikely to be fertile (see Chapter 4). Prior to laying the clutch, the dominant pair spends a lot of time inspecting hollows. They do this in a highly ritualised manner that indicates the behaviour may be an important component of courtship. The pair perches on a branch 10–20 m away from a prospective hollow. One at a time, the birds swoop to the hollow entrance, hang momentarily at its lip, then push off, twisting around as they fall backwards and then fly back to their original perch. Obviously, the belly-flopping element of territorial displays is closely related to nest-inspection behaviour. Once the pair decides on a suitable hollow, they perform almost no preparation of the nest beyond desultorily fussing with the odd woodchip. (This is completely different to the extensive renovation shown by some parrots.) Both members of the pair, but especially the female, will sit in the nest for minutes at a time in the week or two before she lays the clutch; this may make the floor of the nest a little more friable and even. Despite diligent and repeated nest-inspections at many hollows, kookaburras will nevertheless often use the same hollow between years. Around Canberra and in the Dandenongs, about half of the nests used by Laughing Kookaburras in any one year were re-used the following year. Blue-winged Kookaburras at Kakadu National Park re-used over half of the hollows nested in the previous year. Thus, as well as allowing the pair to find a suitable nest, nest-inspection may also serve an important courtship function.

Nest-site characteristics Kookaburras are hollow-nesters. They tend to use naturally occurring tree hollows in dead or living trees, but they will also excavate their own hollows in large arboreal termite mounds where these are common. This is especially relevant for Blue-winged Kookaburras, which tend to live in areas where arboreal termitaria are more common. The dimensions of the nest entrance and the size of the hollow itself are less important than the angle that the hollow slopes away from the entrance. Unlike parrots, kookaburras have weak ineffectual feet and would have a lot of trouble crawling in and out of a hollow that was aligned vertically. Instead, they prefer hollows where the floor is not too far below the lip so that they can shuffle back and forth rather than climb. They are not particular about the height of the hollow, using whatever is available in their habitat; nests for the Laughing Kookaburra have been recorded from as low as 20 cm and as high as 60 m.

Kookaburras typically nest in tree hollows but have been known to nest in some unusual places (such as a hay bale) if tree hollows are scarce.

When natural tree hollows or arboreal termite mounds are scarce, kookaburras have been known to nest in some unusual places, such as haystacks , the stick nests of other birds, holes in walls, and earth banks.

The breeding attempt Egg-laying and incubation The dominant female usually lays three, dull-white eggs in her clutch (see page 66), but sometimes only two. Occasionally clutches of one, four, or even five eggs occur. The clutch is laid with intervals of up to four (usually one or two) days between successive eggs. The incubation behaviour of the female is highly variable at this time – some females begin incubating seriously as soon as they have laid the first egg, some incubate sporadically while they are completing the clutch, and other females delay incubation almost entirely until the clutch is complete or nearly complete. Once the clutch is complete, the female continues to incubate overnight, but during the daytime she is helped by her mate and other group members (see Chapter 6). Hatching Eggs hatch sequentially in the order in which they were laid. The time interval between each hatching event depends partly on the time interval between the laying of each egg, but also on the female’s behaviour during egg laying. Embryos only start developing once the eggs pass a certain temperature threshold (around 27ºC for most bird species), so they need to be incubated for this to happen. If the female begins incubation as soon as she lays the first egg, it gets the maximum head start on later eggs, and the chick will hatch well

Geoff Dabb

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Breeding

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before its siblings – this is called hatching asynchrony. Alternatively, if the female delays incubation until her clutch is complete, the eggs will tend to hatch around the same time because all the embryos start developing at the same time. Consequently, the degree of hatching asynchrony between chicks is quite variable, and this has profound effects on the interactions and dynamics within the brood, as described in Chapter 7. Chicks use the small, white, conical egg tooth on the top of their upper beaks to break out of their eggs (see pages 66–68). After punching a small hole in one side, about 3 mm across, they work their way around the circumference of the egg, leaving the discarded shell in two parts.

Chick development Like all kingfishers, kookaburras hatch blind, pink and naked (see page 66). Despite their apparent helplessness, they are relatively mobile, and are able to shuffle around the nest quite effectively. They are also adept at expelling faecal material from the nest hollow by pointing their rear end in the appropriate direction and propelling the excreta with considerable force – up to 32 inches (80.5 cm) was recorded by one interested naturalist! Their aim is not always accurate, however, and these ‘accidents’ contribute to a festering mess that gradually accumulates on the floor of the hollow. Within a couple of weeks of hatching, the nest floor literally heaves with the wriggles of maggots feasting on waste material and discarded food items. About four days after hatching, the incipient feathers become apparent in tracts just under the chick’s skin. Feathers first erupt through the skin about seven days after hatching, amidst plenty of skin-flaking that gives the chicks the appearance of a bad case of psoriasis. It is fair to say that only their mother could love them at this stage. The eyes begin to open about 10 days after hatching, and take a few days to fully open (see page 67). As the feathers continue to grow, the chick takes on an ‘echidna’ look, because the feathers remain encased in their sheaths and resemble quills. In fact, the feathers remain sheathed in this way until just a few days before fledging. This feature is characteristic of the whole Coraciiformes order, and is probably an adaptation to hole-nesting where the rancid and unwholesome conditions could easily foul unprotected feathers and ruin them. By the time they are ready to fledge, the kookaburra chicks look extremely attractive, not unlike the cuddly toy souvenirs one finds in gift shops (see page 67). The chick’s behaviour changes dramatically during their time in the nest. In the first week or so the young chicks, although blind and clumsy, are extremely competitive and aggressive with each other. The familial atmosphere can get so nasty that the youngest chick is sometimes killed. (see Chapter 7).

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Kookaburras usually nest in tree hollows, high off the ground.

Sarah Legge

Sarah Legge

David Curl


Sarah Legge

Sarah Legge


Sarah Legge

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A clutch of Laughing Kookaburra eggs in the nest (top left), hatchlings (top right), and chicks aged 6, 7 and 8 days old.

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Laughing Kookaburra chicks aged 10 and 11 days (top), a 25-day-old chick (bottom left) and a 32-day-old chick (bottom right).

Sarah Legge

Sarah Legge

Sarah Legge



David Curl

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David Curl

A day-old Kookaburra chick lunging for food.

Young chicks in a typical tree hollow, in eucalypt woodland.

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David Curl


David Hollands

A Blue-winged Kookaburra bringing home a tasty centipede meal for its chicks.

A family of Laughing Kookaburras, shortly after a bout of group cackling.


Russell Smith/Nature Focus

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A Laughing Kookaburra with a captured rodent.

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Russell Smith/Nature Focus


A Laughing Kookaburra tenderising its prey.


David Curl

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David Curl

A Blue-winged Kookaburra visits its three chicks who are nearly fledged.

The tail feathers of a Blue-winged Kookaburra.

Breeding

(a)

(b)

(c)

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The most vigorous chick (usually the oldest) reaps the bully’s reward of being first in line in the food queue. Only once the dominant chick is satiated does the next most dominant chick get a chance to fill its belly. The most subordinate chick, usually the youngest, always gets fed last. As the dominance hierarchies between the chicks are cemented, they fight less, so that by the time they are ready to fledge a brood can appear quite peaceful. However a clear ‘pecking order’ instantly appears whenever an adult group member arrives at the nest with food. After a slightly slow start, chicks put on weight rapidly between days 5 and 25 (about 11 g per day), before gradually slowing down again (Figure 5.1a). There is a suggestion that some mass is lost in the days just before fledging; this weight loss may be mostly due to water evaporation from the growing feathers. The ‘S-shaped’ (or ‘logistic’) pattern of growth shown in Figure 5.1a is fairly typical for birds. The skeletal size of the growing kookaburras increases steadily until about 20 days after hatching, after which growth slows down as the young bird approaches its final size (e.g. tibia length, Figure 5.1b).

Figure 5.1 Changes in (a) weight, (b) structural size, estimated by tibia length, and (c) feather growth, estimated by wing length, for male and female chicks during the nestling period. Each point is an average from 2–49 chicks; 200 different chicks were measured overall.

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Wing growth (which is basically feather growth) shows a different pattern – after a slow start the wings grow steadily (5.5 mm per day) right up to fledging, with no sign of slowing down like mass or bone length (Figure 5.1c). Unlike mass and skeletal size, the wings are not fully grown by the time the chick fledges; the decelerating part of wing growth presumably occurs after the chick has left the nest. Whereas the rate of wing growth is similar for male and female chicks, mass and skeletal size increase more rapidly for females than males. As adults, females are about 13% heavier than males, and the growth curves in Figures 5.1a and b show that females achieve their greater bulk partly by growing more quickly (rather than simply growing for longer). By the time of fledging, female chicks near Canberra are 9% heavier, weighing an average of 311 g compared to a male’s average weight of 286 g. Females are also 2% larger in skeletal size, as measured by the average length of their tibia at 66.2 mm compared to a male’s average tibia length of 64.9 mm. These differences in male and female growth rates have important implications for competitive interactions between brood mates, and are discussed further in Chapter 7.

Fledglings As fledglings, young kookaburras remain dependent on the adult group members for food for several weeks. As well as having to learn where, when, and how to hunt successfully, their half-grown tail and wing feathers make them wobbly and poor fliers. As with many bird species, the first few days after fledging are particularly vulnerable times for the youngsters. When confronted with a potential predator, rather than relying on their woeful flight abilities, young fledglings usually freeze, pointing their beak, head and body in the direction of the threat as though to present the smallest surface area. They can maintain this pose for some time and, from personal experience, it is remarkably effective at making them hard to find. When not trying to be invisible, fledglings can put up an almost constant stream of begging that oscillates up and down in both volume and pitch – designed to drive their carers mad and redouble their food-finding efforts, if only to shut the demanding youngsters up.

Breeding success Although Laughing Kookaburras usually lay three eggs, the number of young they actually fledge is often less. Around Canberra, the average fledging success over four years was 1.4; in Parry’s study in the Dandenongs, the average fledging success was 1.7. Blue-winged Kookaburras at Kakadu National Park usually laid two eggs rather than three, although they may lay three eggs more often in other parts of their range. Nevertheless, like Laughing

Breeding

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Kookaburras, the Blue-winged Kookaburras also fledged fewer young compared with the number of eggs they laid: the average fledging success was 1.3 young. The reasons for this loss in productivity strike at both the egg and the nestling stage, and are described in the next section.

Causes of loss of eggs and young In Laughing Kookaburras around Canberra, the distribution of clutch/brood sizes gradually shifts down over the nesting period. The most common clutch size is three; by the time there are young hatchlings in the nest broods of two and even one chick have become relatively more common. By fledging, this trend is even more pronounced, and many nests have failed altogether (Figure 5.2). Although the largest set of data on mortality rates for eggs and young of Laughing Kookaburras comes from the four-year study around Canberra, the smaller data set from the Dandenongs is valuable because it shows that although the specific figures for different causes of loss for eggs and chicks differ between the sites, the overall qualitative patterns of success are similar. Table 5.1 summarises the mortality rates for eggs, nestlings, and dependent fledglings for Laughing Kookaburras at both study sites. At each place, less than half of all the eggs laid resulted in an independent juvenile two months after fledging. Loss at the egg stage was higher in the Dandenongs than Canberra, but loss at the nestling stage was higher around Canberra.

Figure 5.2 The distribution of clutch sizes, hatchling and fledgling brood sizes for 89 Laughing Kookaburra nests around Canberra that were closely monitored throughout the breeding attempt.

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Table 5.1 Mortality of Laughing Kookaburra eggs, nestlings and fledglings near Canberra and in the Dandenongs. Life-history stage

Percentage died

Cumulative percentage surviving

As an egg

Canberra (254 eggs) Dandenongs (51 eggs)

17% 35%

83% 65%

As a nestling

Canberra (212 chicks) Dandenongs (33 chicks)

32% 18%

57% 53%

Between fledging and independence (2 months post-fledging)

Canberra (125 fledglings) Dandenongs (27 fledglings)

19% 19%

46% 43%

Table 5.2 Breakdown of cause of Laughing Kookaburra egg and nestling loss at Canberra and the Dandenongs. Stage

Place

Eggs

Canberra 9.1% Dandenongs 26%

Nestlings Canberra Dandenongs

Infertility, arrested develop.

Crushing

Tossing

Predation

Disease

Accident

Aband.

Sibling Total comp.

3.1% 0%

2.0% 0%

2.4% 9.8%

17% 35%

1.4% 6.1%

2.8% 3.3% 7.1% 18% 32% 0% 0% 0% 12% 18%

The specific causes of egg and nestling loss are broken down in more detail in Table 5.2. At both sites, most egg loss was due to infertility or arrested development. However, the estimate of 26% for infertility and arrested development in the Dandenongs is much higher than for Canberra’s 9.1% (and higher than most other bird species). The reasons for this are unclear. Very few eggs were lost to predation, especially around Canberra. Birds that nest in holes often enjoy relative safety from nest-predators. In addition, the adult kookaburra’s large size makes it effective at warding off potential troublemakers. However, predation may well be more common in the tropics compared with the figures reported here, where large goannas and pythons could prove harder for kookaburras to fend off. Perhaps because of the larger sample, some rarer causes of egg loss were recorded in the Canberra study. Some eggs were deliberately tossed out of the nest, although the identity of the ‘tosser’ was never determined. In addition, a small number of eggs were squashed or fatally dented. These casualties were particularly interesting, because they occurred in ‘super-large’ groups of seven or more birds. With so many eager but inexperienced helpers shuffling in and out, accidents obviously happen. Egg breakages of this nature were the main

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Peter Marsack

Breeding

An adult watches over two fledglings.

reason why reproductive success in large groups was very low (see section ‘The effect of helpers on breeding success’ in Chapter 6), and this may set an upper limit for optimal group size. In Canberra, most mortality in the nest occurred between hatching and fledging. The biggest cause of nestling mortality was the effects of sibling competition (both through direct aggression and competition-related starvation; see Chapter 7) – over half of the chick deaths occurred in this way. Chicks rarely suffered from predation, for the same reason that eggs were relatively immune. Disease was also rare around Canberra, with very few chicks appearing sickly before their disappearance. Many kookaburra nests support a lively maggot fauna in the debris on the floor of the nest. In most cases, these cause no harm to the nestlings. In fact, large numbers of maggots in the nest may provide a useful hygiene function. Occasionally, however, these maggots (possibly Passeromyia sp.) attach to the chick’s skin, and become deeply embedded (see picture on the next page). At the very least this must be extremely uncomfortable for the chicks, and perhaps if a chick was weak or ill, an attack by bloodsucking maggots might be enough to tip it over the edge. Unforeseeable accidents, such as nest cave-ins or branch-breakages killed a small number of nestlings. Finally, some broods were abandoned, for unknown reasons. In the Dandenongs a smaller proportion of hatchlings died


Sarah Legge

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Occasionally some types of maggots in the nest hollow attach to the chicks, like this maggot that is buried between two of the chick’s toes.

before fledging. Sibling competition may have been weaker there (although the sample size was quite small) because the Dandenongs are relatively lush compared with Canberra, and many of the study groups were artificially fed by people living in the area. The different rates of sibling competition between the two sites may therefore be explained by differences in the amount of food available to the provisioning adults. The most common sources of mortality for fledglings in both study sites were predation (inferred from the sudden disappearance of an otherwise healthy fledgling) and starvation (usually the youngest member of a brood who was notably underweight at fledging). Comparable data are available for Blue-winged Kookaburras in Kakadu National Park, and they show broadly similar patterns. Like Laughing Kookaburras, about half of all Blue-winged Kookaburra eggs laid resulted in a fledgling (51% of 61 eggs). The estimate for unhatched eggs due to infertility and arrested development was similar to that of Laughing Kookaburras around Canberra, at 7%. During the nestling phase, starvation, sibling competition and disease together claimed about one-fifth of all chicks, which is also similar to the data from both Laughing Kookaburra studies. Nest loss due to accidents like flooding and fire occurred in about one-tenth of nests, which is more common than for Laughing Kookaburras, reflecting the vagaries of a monsoonal climate and the high fire frequency of tropical woodlands. Predation was also slightly more common, affecting just over one-tenth of nests, probably because of the presence of larger predators like olive pythons, goannas and quolls.

6 The helping system

A

ll group members help to incubate the eggs and brood the nestlings when they are young. They also feed the nestlings and fledglings, provide a sentinel system and defend the young against potential predators. As discussed in Chapter 4, caring for the offspring of others rather than simply breeding oneself is a trait of special theoretical interest for evolutionary ecologists. Over 20 years of research on many species of cooperatively breeding birds worldwide has resulted in a plethora of different hypotheses to explain this behaviour. Before we can suggest why kookaburras are cooperative, we need to describe their social, mating and helping systems in detail. Chapter 4 dealt with the social and mating systems. This chapter details information on the helping system of the Laughing Kookaburra. The first section characterises the contribution that each Laughing Kookaburra group member makes to the corporate breeding effort. The size of this contribution depends on the size of the group, whether the individual is a dominant bird or helper, its sex, the number of chicks in the brood and the age of the chicks. Then the complicated effects that this help has on the breeding success of the group are described. The final section synthesises this with what we know about the social and mating systems to suggest reasons why cooperative breeding may have evolved in the Laughing Kookaburra.

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Incubation As mentioned earlier, the dominant female usually incubates overnight, but during the day any group member may incubate. All kookaburras in the group, dominants and helpers, males and females alike, develop a brood patch – an unfeathered area on the belly that becomes highly vascularised during breeding in order to help incubate eggs and brood chicks effectively. When a bird feels ready to exercise some of its parenting skills, it perches near the nest entrance, making soft contact calls. This alerts the incumbent incubator that a break is on offer. Sometimes the incumbent is reluctant to leave, so if the potential replacement is feeling really keen, it flies into the nest anyway to try and encourage the sitting bird to leave. Incubating or brooding birds will also exit the nest unprompted without being immediately replaced, presumably when they are hungry (or bored). In Laughing Kookaburras, the amount of time a bird spends incubating during the day depends on its dominance status and sex. The dominant male incubates the most, followed by the dominant female. Helpers incubate less, but again male helpers are more diligent than female helpers (Figure 6.1). The dominant pair performs most of the incubation duties irrespective of group size.

Feeding young All Laughing Kookaburra group members contribute to feeding young; they bring back food items to the nest and pass these to the nestlings directly.

Figure 6.1 On average across groups, breeding males perform most of the daytime incubation duties, followed by the breeding female. Helpers chip in relatively small amounts. The breeding female usually incubates overnight.

Figure 6.2 Chicks receive most food when they are growing fastest, between 15 to 25 days after hatching. The data for each bar come from 14–28 broods.

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Sarah Legge

The helping system

Hungry kookaburra chicks compete agressively for food; the youngest chick sometimes gets killed by its competitive siblings.

Before entering the nest, they perch nearby from a few seconds up to a couple of minutes, squawking softly. This often prompts a surge of vigorous begging and jostling by the chicks as they jockey to gain the key position facing the hollow entrance. The amount of food brought to the nest increases as the chicks age until the third week. This is the period when the chicks are gaining weight most rapidly (see ‘Chick development’ above). The amount of food delivered then declines as the chicks approach fledging (Figure 6.2). During this stage the chicks are not gaining much mass but feather development continues unabated. As well as being sensitive to the age of the chicks, adults also respond to the number of chicks in the brood, bringing more food to nests containing larger broods. Although you might expect large groups to bring more food to the nest than small groups, this is not the case – a group of six birds brings back the same amount of food to a brood of a given size and age compared with an unassisted pair. This suggests that individuals in larger groups are reducing their workload, and if we look closely at an individual’s contribution towards the corporate feeding effort, it turns out that they vary their workload in response to several factors besides brood size and chick age. Males bring more food to the nest than females – this is true for both the dominant birds and the helpers irrespective of group size (Figure 6.3). Group

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members in larger groups bring less food to the nest than those in smaller groups; this effect is especially pronounced for helpers, who really slack off if they are in a larger group. The net effect of these influences of breeding status, sex and group size is that male breeders are always the primary foodproviders, working harder than any other group member. Female breeders and male helpers work at roughly the same intensity, but female helpers are woeful. Once they have arrived at the nest, female helpers are also more likely to fail to deliver the food to the chicks. The incidence of ‘failed feeds’ by other birds in the group varies from 0–0.03, but for female helpers the proportion is 0.21. In other words, in one feeding trip out of five they never actually get the food to the chicks, instead swallowing it themselves! There is one other factor that might be expected to affect feeding effort, but does not – the relatedness of the helper to the brood. Chapter 4 explained that some kookaburra groups are actually step-families, where one of the breeders is unrelated to the helpers in the group because it recently replaced the helper’s deceased parent. In these groups, helpers are providing care to half-siblings rather than full relatives. In many other species of cooperatively breeding birds that have similar step-family arrangements, helpers provide more care if the brood is comprised of full siblings rather than step-siblings. This is not true for Laughing Kookaburras, and it gives us the first hint that the indirect benefits gained from increasing the production of non-descendant kin in each breeding attempt is not an important selective pressure maintaining cooperation in this species.

Figure 6.3 Male breeders are the most diligent providers, but they do relax their efforts if there are helpers in the group to take up some of the burden. At each group size, the birds from two to seven different groups were observed for this analysis.

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The helping system

An adult kookaburra at the nest hollow.

The effect of helpers on breeding success Most bird species that breed cooperatively live in family groups, and this has promoted the idea that kin selection is an important evolutionary force behind cooperative breeding. In other words, helpers could increase the number of young their relatives (often parents) produce in each breeding attempt, or in each year (by increasing the number of breeding attempts), or over their relative’s lifetime. If the relative needs to work less hard to raise each young, it may live and reproduce for longer. In fact, the data to support this idea is quite inconsistent across species of cooperative breeders, and it is worthwhile for us to examine this issue in some detail for Laughing Kookaburras, in order to understand why they breed cooperatively. Since kookaburras are single-brooded, helpers can not increase the breeding success of their parents by increasing the number of breeding attempts in a season, but they could affect the success of each breeding attempt. To examine whether helpers do influence productivity, we can look at the success of breeding attempts at three successive stages – clutch size, hatching success, fledging success. Figure 6.4 shows that helpers do not affect the number of eggs a breeding female lays in her clutch. However, fewer eggs hatch successfully in the largest groups of seven or more birds. The hatch failure in these super-large groups is caused by physical damage to the eggs – denting and squashing. It

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seems to be a case of ‘too many kookas spoiling the broth’ – all the comings and goings of enthusiastic but clumsy helpers during incubation result in inevitable accidents. By the fledging stage, a different pattern emerges. The super-large groups still perform poorly – they can not easily recover from squashing most of their clutch! But now it appears that unassisted pairs and small groups also suffer a drop in productivity (Figure 6.5). Between hatching and fledging they lose more of their chicks than larger groups. On the face of it, this looks like support for the idea that helpers increase the production of relatives. But a relationship like this could be explained in another way: if a breeding pair are routinely successful at producing young (either because they are high quality parents, or because their territory is an especially lucrative piece of real estate), they will be in larger groups because they are always producing potential recruits. In contrast, a breeding pair that is poor at producing young may rarely have independent young that it can recruit to be helpers. This circularity could generate a spurious relationship between group size and breeding success. To find out if larger groups produce more young because of the helpers or because of the intrinsic quality of the parents or territory, we need to look at the performance of the same breeding pair when it has different numbers of helpers assisting with the breeding attempt. I tested this with 24 pairs of kookaburras around Canberra. Each pair bred with different numbers of helpers in different years, and I compared the success of their attempts when the number

Figure 6.4 Clutch size is similar for all group sizes, but very large groups have low hatching success compared with smaller groups. Fledging success is highest for medium-sized groups. The data for clutch size and hatching success come from 89 nests; the data for fledging success are from 131 nests.

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Figure 6.5 This graph shows the relative change in fledging success between two breeding attempts. When a Laughing Kookaburra group increased in size fledging success was equally likely to increase or decrease. When the number of male helpers in a group increased (with the number of female helpers unchanged), the pattern was similar. But when the number of female helpers increased (with the number of males staying the same), fledging success usually decreased.

of helpers changed. The results were fascinating: Figure 6.5 shows that, overall, the number of helpers made no difference to the success of the pair. If the number of helpers increases, the pair is as likely to do worse that year as better. However, if we take the sex of the helpers into account, it appears that male and female helpers have very different effects. When the number of male helpers increases, but the number of female helpers stays the same, the fledging success is unaltered. In other words, male helpers are neutral with respect to fledging success. In contrast, when the number of female helpers increases, but the number of male helpers stays the same, fledging success decreases (Figure 6.5). In other words – female helpers are very bad news. This negative effect is not apparent at hatching, which shows that their detrimental influence takes hold during the nestling phase. In the description of the helping system above, we learnt that individuals in larger groups decrease their feeding effort. We also learnt that female helpers are poor provisioners, bringing back less food to the nest than other birds in

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the group. Perhaps group members gauge their appropriate feeding contribution based on the number of helpers in the group but ignore the sex of these helpers; if some helpers are female, birds will therefore underestimate how much food they should bring back. This would result in lowered overall food deliveries, which would affect the growth and survival of chicks. Whatever the mechanism for female helpers decreasing the reproductive success of their groups, it is clear that in general helpers do not boost the breeding success of their parents, and therefore the positive correlation we see between group size and fledging success is not causal. Rather, ‘better’ pairs (either because of their own intrinsic high quality, their territory’s quality, or both) produce more young and therefore tend to have more helpers around them.

Why do helpers help? The previous sections have shown that one potential and obvious reason for helping – increasing the success of the breeding attempts of your relatives – does not apply to Laughing Kookaburras. Nor does helping increase the number of breeding attempts in a season – kookaburras are single-brooded. This leaves us with the possibility that helpers ‘help’ by reducing the workload of their parents, which might result in a longer reproductive life for them, and hence more offspring. In the section ‘Feeding young’ above, we have seen that individuals in large groups, including the breeders, work less hard because they decrease their provisioning effort to the brood. Does this translate into enhanced survivorship for those individuals? Unfortunately, this is a very hard thing to test – kookaburras are long-lived (10–15 years), and we would need to know the lifetime reproductive success of many birds before we could even attempt to examine this question. However, the story as told so far does imply that ‘load lightening’ (reducing the workload of the parents) may be an important selective force maintaining the helping behaviour of Laughing Kookaburras. There are two pieces of evidence supporting this. First, the biggest single cause of productivity loss during a breeding attempt is brood reduction. Brood reduction in Laughing Kookaburras is a complex issue dealt with in detail in Chapter 7, but its ultimate cause is food shortage. If food is limiting, you would expect larger kookaburra groups to capitalise on their increased feeding potential, raise the overall feeding rate to the brood and thus prevent nestling starvation. This is true of the vast majority of cooperatively breeding bird species where nestling starvation is an important source of productivity loss – more helpers usually means more food to the brood. Laughing Kookaburras are an exception to this rule. Instead of boosting the corporate effort, each individual in the group

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The helping system

When chicks are growing fast, the adult group members constantly ferry food back to the nest.

decreases their own contribution so that the overall feeding rate by a group of six kookaburras is the same as that of an unassisted pair. This strongly suggests that the personal gains achieved by reducing the workload are worth more than the production of an extra chick or two. Second, young females are the worst helpers. They share the same genetic relationship with the brood as their male counterparts, so the difference in their helping behaviour is probably related to the different costs each sex incurs from feeding young. As adult females are over 13% heavier than males, they need to eat a greater absolute amount of food during the day in order to maintain their own body condition. If provisioning young is generally costly, it is probably that much harder for females, especially when they are young and relatively inexperienced hunters. Related to this is the observation that as group size increases, the helpers reduce their contribution more than the breeders – again, helpers are younger, relatively less experienced hunters and provisioning young is probably more costly for them than for the breeders, so they slack off at the earliest opportunity. The conclusion that provisioning young is costly lends weight to the idea that load lightening is an important benefit of helping. Besides load lightening, there are other non-exclusive potential benefits of helping. For example, young birds may gain valuable breeding experience. This is unlikely to be a strong effect in Laughing Kookaburras, because

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kookaburras nesting together for the first time, with little or no breeding experience, do just as well as birds that have been paired for years. In addition, the age of breeding birds has no effect on their success. Together, this suggests that experience is not an important influence on breeding success. Alternatively, by staying in their natal territory, young birds have a safe place to hang out while they keep their ear to the ground for breeding vacancies nearby. Of course, the parents should only allow this as long as it does not inflict a cost on them, for example by depleting resources on the territory. Viewed in this light, helping to raise young could be considered a kind of ‘rent-payment’ to indulgent parents for the privilege of not being booted out. One other way that young Laughing Kookaburras might help their parents is not related to the care of young. Helpers are very involved in defending the territory – they team up with their parents, joining in the group choruses as well as the ritualised flight behaviours at territory borders. Larger groups have louder and longer choruses, and these choruses probably convey information about a group’s size and composition to its neighbours. However, we do not really understand the role of helpers in this context, in terms of whether they do indeed help their parents maintain a larger territory or stop them from being squeezed out by imperialist neighbours. As mentioned in Chapter 3, dramatic changes in group size between years are not always accompanied by concomitant changes in territory size. However, there may be some inertia associated with shifting the position of territory boundaries. If helpers do assist in maintaining larger territories, it is possible that the real benefit is not the size per se, but the greater range of microhabitats (and therefore prey types) it contains, which could represent a buffer to fluctuating climatic conditions and resource levels. So by letting some of their young stay at home, parents may reap the rewards of a larger group-territory at no additional expense to themselves, which might have a positive effect on their breeding success in difficult years.

7 Life in the nest

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he previous chapter demonstrated that kookaburras cooperate to raise young using complex rules. Because they live in family groups, kookaburras are in a position to help their relatives and gain indirect genetic benefits. However, this help must be carefully bounded so that the costs of the behaviour (e.g. loss of independent reproduction, costs of feeding) do not outweigh its benefits (e.g. increased survival of parents, who can therefore produce more non-descendent kin). This complexity is mirrored by the interactions between chicks in the brood, yet in a reverse way. Each chick needs to sequester as much of the resources as it can to optimise its own growth and survival chances. However, its competitors are relatives, so a chick’s selfish behaviour needs to be held in check when the harm to relatives is so great that the indirect fitness losses outweigh the direct fitness gains. Although this taut balance is true for a brood of any species of bird, it is all the more poignant in kookaburras because a kookaburra chick is capable of killing its siblings. Siblicide is a relatively rare phenomenon in birds, and the kookaburra is the only cooperatively breeding species so far known to exhibit this remarkable behaviour. This chapter will first outline some background to avian siblicide, before describing how kookaburra chicks fight, when the aggression becomes fatal, and why it occurs in some nests and not others. We will also see how parents

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control the process, and what happens when parents ‘get it wrong’. The information is drawn from the study on kookaburras around Canberra by myself and Anjeli Nathan, who studied aggression in kookaburra chicks in great detail by installing miniature surveillance cameras inside nest hollows.

Siblicide in birds Siblicide is usually defined as the death of offspring caused by substantial aggression from siblings. This definition excludes the many species where competition (even boisterous competition) for resources leads to the weakest individual in the brood doing poorly and eventually starving to death as a consequence. It does, however, include species where aggressive attacks from one or more chicks so intimidates the victim that it stops trying to get food (e.g. cattle egrets). Classic well-known examples of siblicidal species include some of the eagles (e.g. black eagle of Africa), where the oldest chick attacks its younger sibling even as it tries to emerge from the egg, and maintains a relentless pecking assault, breaking skin, drawing blood, and eventually either killing its younger sibling outright, or harassing it so much that it fails to feed and dies of starvation. In some species, like ospreys, aggression is a facultative response to food shortages – as the chicks get hungrier, they fight more, and eventually the weakest one succumbs. Facultative siblicide is essentially a ‘resource-tracking’ device – a way of pruning the brood size should conditions warrant it. It only happens in those nests where, for whatever reason, the parents can not provide enough food. In other species, like masked boobies and black eagles, siblicide is virtually inevitable in all nests, and takes place very soon after hatching when the chicks are still so small that hunger is unlikely to be the proximate cue for aggression. Indeed, it is often apparent that there is a glut of food at this time, with uneaten debris strewn around the nest. Parents in these ‘obligate siblicidal’ species are rarely, if ever, seen to interfere with the fighting. Unlike facultative siblicide, obligate siblicide seems paradoxical and wasteful. Why do the chicks fight when there is plenty of food? Why don’t the parents stop the fighting (and therefore produce more young), and if they are not prepared to stop it, why do they bother laying the doomed egg in the first place? The answer is probably that the brood reduction in obligate siblicidal species pre-empts an anticipated food shortage later in the nestling period, when the chicks are large and growing fast. If the parents can not supply enough food to the brood at this time, the weaker, younger chick will die anyway. If a chick’s death is inevitable, it is better to dispatch it as soon as possible after hatching so

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Sarah Legge

Life in the nest

Two chicks, just a couple of days from fledging. Their third sibling was killed soon after hatching.

that time and energy are not wasted feeding a doomed offspring. The available food can then be diverted into the chick that is going to survive. The question remains – why do parents bother laying the doomed egg if they have no intention of raising it? Obligate siblicidal species have small clutch sizes, often laying just two eggs, at most three. They consequently usually rear just a single (or two) young. If they laid just one egg, they risk raising no young at all if that egg fails to hatch. To safeguard themselves against this possibility they lay an additional, sacrificial egg as an insurance policy against hatch failure in the first egg. Should the entire clutch hatch, they need an efficient way of cancelling their insurance policy. They could simply kill a chick themselves, but this would require them to make a subjective assessment of which offspring is the weedier. Instead they take advantage of hatching asynchrony, which effectively handicaps one chick by making it younger than its older sibling, and then rely on aggression from the older sibling(s) to carry out the dirty work. Allowing the chicks to fight it out ensures that the weakest chick is killed; if the older chick is debilitated or weakened for some reason, the younger chick may survive and even kill its older sibling.

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Fighting in kookaburras From the circumstantial evidence of wounds on the smallest chicks followed by their sudden disappearance, it is clear that both species of kookaburra have siblicidal young. The process has been studied in detail for Laughing Kookaburras, but it is likely that much of what follows below applies to the Blue-winged Kookaburra as well. Kookaburra chicks are aggressive from the moment they emerge from their egg. Older hatchlings will even attack their siblings through the small hole in their eggshells made when they first start to hatch. Undeterred by their blind clumsiness, they flail around madly looking for a piece of sibling anatomy to latch onto. For this task, they are equipped with a sharp, downward-pointing hook at the end of their upper beak. This beak hook grows out and has disappeared by the time the chick is ready to fledge; such morphological specialisations for sibling rivalry are rare in birds (see also page 68). If an aggressive chick manages to grip part of one of its siblings, it shakes the unfortunate victim furiously. Chicks also engage in lunging pecks that often break the skin and result in beak-shaped scab wounds on the back and head of the victim. The most dangerous grapple, however, is when the aggressor manages to grip its victim around the base of the skull, with its beak hook buried just under one ear. By applying pressure and shaking violently, the aggressor is apparently able to kill its victim outright. During my field study near Canberra I found several tiny corpses with heavy, telltale bruising around their necks and heads.

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As Sarah Legge

In a newly hatched chick, the downward-pointing hook on the end of the upper beak is sharp and obvious. Note the egg tooth on the top of the upper beak. As the chick ages, the beak hook gradually grows out and becomes less sharp.

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Sarah Legge

Life in the nest

In some nests, young chicks fight at every opportunity. A chick can suffer quite severe wounds to the head in an attack from an older sibling (bottom right).

the chicks mature, the frequency of fighting steadily diminishes. This can be inferred from the declining incidence of fresh bruises and wounds seen on chicks as they get older (see Fig 7.1). Tiny surveillance cameras placed into the roofs of nest hollows proved that this inference is valid – quantifying the levels of aggression between brood mates showed that chicks do indeed become more peaceable with every passing day. Immediately after hatching, chicks invest much energy trying to keep or better their place in the dominance hierarchy that automatically exists because of their age differences. However, once a series of contests clearly establishes who the consistent winner is, fights become less frequent – there is little point contesting something you are unlikely to win.

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Figure 7.1 The incidence of fresh wounds on chicks declines as they age and fighting becomes less frequent. Data from 175 chicks was used for this analysis.

An historical aside Before Anjeli Nathan and I began our research into siblicide in kookaburras, other biologists had peered into kookaburra nests and seen the same signs that we had, without recognising the grizzly behaviour for what it was. For example, in the 1940s Keith Hindwood, possibly the first person to make detailed observations at kookaburra nests, wrote: ‘I noticed a young bird, one day old, attempt to nibble or bite the neck of a fellow nestling; no doubt this was an instinctive reaction when its bill came into contact with the other bird’s body.’

These days, we might have a more sinister interpretation of this observation. The next doyen of kookaburra life was Veronica Parry, who studied a small number of groups for two years in the Dandenongs in the 1960s. Siblicide was certainly occurring in her study population – she writes of the sudden disappearance of apparently healthy chicks and of noting scabs on the chicks before their disappearance. Yet, like Keith Hindwood, she failed to put the pieces together. Why did these earlier observers ‘miss’ this extraordinary behaviour? Nowadays, biologists assume that individuals behave in ways that maximise their own fitness, or genetic contribution to the next generation. This viewpoint can include apparently altruistic behaviour like helping, as long as the behaviour results in a greater representation of the individual’s genes in the next generation. This viewpoint also has no trouble explaining why a chick should kill its sibling – the chick loses indirect genetic benefits from the death of a relative, but as long as it gains enough direct fitness benefits (e.g. more

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food, better personal survival) to offset this loss, the aggressive behaviour will be selected for. In contrast to this view of individual selectionism, earlier biologists like Hindwood and Parry were operating under the paradigm of group selectionism, whereby individuals are expected to behave in ways that benefit their population or species. No-one would expect chicks to kill relatives – it is patently bad for the relative and bad for the parent, and lowers the productivity of the population. In other words, although both Hindwood and Parry had the evidence before them, they lacked a motive, so they did not ‘see’ the behaviour. This is a good example of how our intellectual preconceptions influence our interpretation of facts; who knows what future biologists will think of some of the things we say these days!

When and where does siblicide occur? Around Canberra, about one-third of nests with two or three young in them experienced siblicide each year. The youngest chick was always the one to succumb, and usually died within four days of hatching; at the latest, death occurred within eight days of hatching. Kookaburra siblicide seems ‘obligate’ because it happens long before feeding rates and chick growth rates peak at between 18 to 25 days after hatching. However, the frequency of nests in which it occurs (one-third) is much lower than for most obligate siblicidal species, which have siblicide rates of over 90%. Why does siblicide only happen in some kookaburra nests and not others? The following section describes the factors that result in elevated aggression, and the death of the youngest chick. We might expect siblicide to be more common in broods where the competitive disparities between chicks are most pronounced, because then the youngest chick would be most disadvantaged. In fact, the story is more complex. Siblicide of the third-hatched chick is actually most common when the first and second-hatched chicks are similarly matched in terms of their fighting abilities. This paradoxical statement can be understood if we think about contest theory, which predicts that fighting will be most intense when opponents are similarly matched, because the outcome of the fight is unclear. In contrast, if opponents are very disparate, there is little point in fighting since the outcome is a foregone conclusion for both of them. In a kookaburra brood, when aggression escalates between the first- and secondhatched chicks, the third-hatched chick (being younger, less mobile and less able to defend itself) gets caught in the crossfire of its older siblings and dies as a result. There are three attributes of the older two chicks that could (and do) affect the degree of competitive disparity between them: the age difference

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between them (i.e. the hatch interval), the difference in their size when they first hatch, and their sexes (because females grow faster than males).

Hatching interval Older chicks have better-developed motor skills as well as being physically larger because they have been growing for longer. Obviously, this competitive advantage will diminish with shorter hatching intervals. In kookaburra broods, when the hatch interval between the first and second kookaburra chick is short (under six hours) the third chick is nearly always killed (Figure 7.2). This agrees with the prediction of contest theory – as the hatch interval between the older chicks decreases and the direction of dominance between them is muddied, they should fight more enthusiastically. The second-hatched chick has a real chance of winning top position in the dominance hierarchy, and conversely, the first-hatched chick faces the real prospect of losing its prime position, and will therefore go to greater lengths to persuade its sibling of its rightful place. The hapless third-hatched chick suffers disproportionately from the violence unleashed in its nest. This inferred explanation was confirmed with the help of surveillance cameras. In nests where the first and second chick hatched close together in time, levels of aggression were higher compared with other nests, especially in the first few days after hatching, when siblicide is most likely to take place (Figure 7.3).

Figure 7.2 When the first and second chicks hatch close together in time, the third-hatched chick is nearly always killed. Siblicide is less common when the first and second chicks hatch asynchronously. These data are from 46 nests.

Figure 7.3 The second-hatched chick attacks its older sibling much more when the age difference between them is small. Generally, aggression decreases as the chicks age. These data are from 11 pairs of siblings from different nests.

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Figure 7.4 In nests with siblicide the first and second chicks hatch from eggs that are similar in size, while the third chick hatches from a relatively small egg. In nests without siblicide the eggs decrease in size more steadily. These data are drawn from 42 broods.

Size at hatching A chick’s position in the hatching sequence will have a big impact on its size relative to other chicks. In addition, chicks can also be different physical sizes immediately after they have hatched out of their eggs, and this could amplify or reduce any size advantages due to age differences. The size of a chick at hatching is closely correlated with the volume of the egg it hatched from, so we can use egg volume (calculated from the length and width of the egg) as a convenient measure of hatchling size. Once again, siblicide was more common in nests where the first- and second-laid eggs were similar in volume (Figure 7.4). So, as well as being wellmatched in terms of age, siblicidal seniors were also well-matched in their initial physical size, further confusing the direction of dominance between them. Surveillance cameras confirmed that aggression between the older two chicks was higher when they hatched at similar sizes. In addition, the third egg in siblicidal nests was particularly small (Figure 7.4). This seems ‘sensible’, since if the third egg is only being laid as insurance, the breeding female should only form an egg that is just big enough to be viable. It probably also ensures the third chick is killed more easily, because it is much smaller than its older siblings. The sex of chicks Because females grow more quickly than males, the sequence of sexes in a brood has significant effects on the competitive interactions between chicks. If a female hatches first, and a male second, she enjoys an age advantage, an additional size advantage (because she probably hatched from a larger egg),

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and also her natural growth advantage. In this scenario, the direction of dominance between the two chicks is likely to be very clear, and fighting minimal. In contrast, if a male hatches first followed by a female, dominance will be unstable, because his age and size advantage is quickly eroded by his sister’s faster growth. This is exactly what we find when we look at kookaburra broods with different sex sequences of young – those where a male hatches first and a female hatches second have a higher incidence of siblicide (Figure 7.5).

The kookaburra siblicide syndrome Nests that experience siblicide do not have just one of the aggression-encouraging attributes described above; they usually have all three. Siblicidal nests are those where the first and second chicks hatch close together in time from eggs that are similar in size, and where the sequence of sexes is male-female. When these conditions co-occur, siblicide is usually inevitable, or obligate. There is one other feature that distinguishes siblicidal from non-siblicidal nests – siblicide is more common in nests attended by groups lacking male helpers (Figure 7.6). This is not because these smaller groups bring less food to the nest – Chapter 6 showed that small groups were able to sustain the same feeding rates as larger groups. In any case, siblicide occurs well before feeding rates are high. Rather, the size of a group reflects the past reproductive performance of the breeding pair. If they lack male helpers, it may be because they are habitually poor breeders that have trouble feeding all their young. Siblicide in these broods is therefore apparently a pre-emptive first strike against anticipated food shortages later in the nestling period. The next question, then, is: who is doing the ‘anticipating’?

Figure 7.5 Siblicide is most common in nests where the first chick is male, and the second is female. These data are from 51 nests.

Figure 7.6 Siblicide is more common in nests belong to groups with no male helpers. The data are from 53 nests.

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Who controls whether siblicide occurs? So far we have identified the proximate set of conditions that ‘make’ siblicide happen. But how do these conditions arise? Is siblicide just an unfortunate byproduct of a constellation of brood attributes, or is it adaptive in some way? The evidence strongly suggests that parents engineer a siblicidal environment in their brood, and they do this to reduce their brood size to a manageable size before food demands peak. The three brood attributes that influence aggression (hatch intervals, egg sizes and chick sexes) are all potentially under parental control. As explained in Chapter 5, the hatch intervals between chicks are determined by the behaviour of the breeding female while she is laying the clutch. In non-siblicidal nests, which have a longer hatch interval between the first and second egg, the female began incubating soon after starting the clutch. The mothers of siblicidal broods delayed incubation at least until they laid the second egg, causing the first and second eggs to hatch together. Breeding females are not making conscious decisions about their incubation behaviour. The different incubation patterns by mothers of siblicidal and non-siblicidal broods are more simply explained by the immediate constraints of food. Incubation and hunting are mutually exclusive behaviours. If a female is in relatively good physical condition after starting her clutch she can begin incubating immediately, even though this conflicts with hunting. In contrast, if she is in poor condition, she may be forced to keep hunting for herself after laying the first egg, delaying incubation until later. The different patterns of egg sizes in the clutches of siblicidal and non-siblicidal broods can be explained by the same feeding constraints during egg laying. Females that delay incubation and continue to hunt may have more readily available resources to pump into that second egg compared to females that essentially fast after laying (and sitting on) their first egg. Note that poor quality females are precisely those that are unlikely to have helpers. Courtship feeding of the dominant female by helpers probably plays an important role in keeping her in tiptop condition leading up to egg laying. In addition, since helpers are a reflection of her past track record at raising young, females without helpers are probably those that always tend to ‘struggle’ and fail to produce large broods. To summarise, the female’s condition at time of laying is a yardstick for that group’s ability to look after hungry nestlings. Poor physical condition results in behaviour during egg laying which inadvertently creates a hypercompetitive environment in her brood, the early death of the youngest chick, and adaptive brood reduction from the perspective of the parents (because they probably were not capable of raising all their young). Not content to rely on age and size similarities alone to make dominance between the chicks

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The breeding female sits in the nest and watches her chicks fight. Parents never intervene in the aggression, like all other siblicidal birds. The brooding patterns of adults in siblicidal and non-siblicidal nests differ. Siblicidal chicks are brooded less, and in relatively shorter, more frequent bouts, which keeps them warm but gives them ample opportunity to fight. (Images captured from surveillance video by Anjeli Nathan.)

unclear, the breeding female also manipulates the sex of her offspring (male first, female second) to make sure that agression breaks out. At this point, we have no idea how birds manage to control the sex of their young, as they have a chromosomal sex determination system similar (but in reverse – females have two different sex chromosomes instead of males) to humans. But examples of adaptively biased sex ratios are accumulating from an ever-increasing number of bird species. The evidence presented above strongly implicates the kookaburra mother as chief architect of bedlam. However, having set up these hyper-competitive situations, the parents of murderous chicks are not content to simply sit back and watch. Their brooding patterns differ from those of parents of non-siblicidal broods in ways that encourage fighting. Chicks can only fight when they are not being brooded. However, young chicks are unable to thermoregulate, and if they are left uncovered for too long their body temperature drops, they become torpid and unable to move around and fight. The best brooding pattern to maximise fighting time is therefore to brood in short but frequent bouts, so the chicks stay warm enough to function but have enough time to work up a good head of steam in the boxing ring. This is exactly the brooding pattern we find in siblicidal nests.

Is siblicide adaptive? It seems clear that kookaburra parents create and encourage siblicidal conditions in their broods. Siblicide appears to be a pre-emptive brood reduction strategy to eliminate the insurance offspring of poor quality parents that are unable or unwilling to raise a full brood. If siblicide in kookaburras is

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When parents overestimate the size of the brood they can provision, they are likely to have trouble bringing back enough food when chicks are growing fastest.

adaptive, then parents who get it wrong should suffer lowered reproductive success. For example, poor quality parents with a siblicidal brood should fare better in the end than similar parents who try to raise three young even though they are not really capable. The best way to explore this would be by experiment – preventing the death of the youngest chick in siblicidal nests, and following the subsequent progress of the brood. However, this would be logistically difficult. Luckily, we do have some illuminating natural data on what happens in a brood when parents make ‘mistakes’ of this nature. When parents overestimate the size of the brood they can provision, they are likely to have trouble bringing back enough food to the nest when the chicks are growing fastest and have their highest feeding requirements (15–25 days after hatching). In our study around Canberra, we noticed that in about one-fifth of nests chicks were starving to death 14–25 days after hatching, exactly the period when feeding rates are highest. These late deaths were quite different from the siblicidal deaths – the chicks were not wounded before their disappearance (indicating they did not die from direct aggression) but were emaciated and under-developed (suggesting gradual starvation). Losing a chick at this stage, after considerable investment already, is relatively costly for parents. Had they ‘known’ their chick would starve at this late stage, they would have been better off encouraging siblicide earlier on. Late starvation appears to be an example of what happens when parents ‘miscalculate’ how many chicks they can adequately feed.

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In nests that experienced late starvation, the growth of the surviving chicks was compromised, indicating that food was stretched thinly in these nests. Figure 7.7 summarises various growth parameters for the oldest two chicks in nests where the third-hatched chick survived, nests where the third-hatched chick was killed by attacks from its oldest siblings, and nests where the third chick died of starvation late in the nestling period. In nests where the youngest chick starved, the surviving older chicks suffered a growth penalty – they were stunted in terms of skeletal size and had retarded wing growth compared to their counterparts from other nests (Figures 7.7a and 7.7b). They managed to fledge at similar weights to older chicks in nests where the youngest chick survived; presumably they ‘caught up’ once the youngest chick actually died (Figure 7.7c). However, they were still considerably lighter than older chicks that killed their youngest sibling. a b

c

Figure 7.7 These graphs compare the growth of older chicks from broods that experienced no mortality, broods where their youngest sibling died from siblicide within days of hatching, or from starvation much later in the nestling period. In broods where the youngest chick starved to death, the surviving older chicks appear stunted in size, although they have caught up in weight. If the youngest chick died from siblicide, the surviving older chicks are skeletally large, and also relatively ‘fat’. These data are from 93 broods.

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The poor growth of the surviving chicks in broods where the youngest chick starved may have long-term consequences for their survival and reproductive potential. Heavier fledglings are much more likely to survive the postfledgling period while they are learning to hunt for themselves (Figure 7.8). Moreover, they are more likely to find a breeding vacancy once they are mature (Figure 7.9). So fledging at a low weight and/or size really stacks the odds against a chick. If mistakes about the appropriate brood size are this costly, it seems surprising at first that they occur so frequently (in one-fifth of nests). However, mistakes are probably inevitable because the brood characteristics that result in escalated aggression are set in motion during egg laying, weeks before food becomes limiting. Conditions could easily change during that interval. A human analogy would be an economist trying to predict the stock market – a player may get it right most of the time, but the odd blunder is virtually unavoidable. Although late starvation can be viewed as a mistake on the part of parents who should have had a siblicidal brood, nevertheless it is probably still adaptive, given the circumstances, in the sense that it ensures damage-abatement. Without this relatively costly delayed brood reduction, the available food would need to be stretched very thinly between the whole brood, resulting in even poorer growth and performance (and perhaps even death) of all the chicks.

Figure 7.8 Chicks are more likely to survive the critical two-month period after fledging if they are heavy when they fledge. These data come from 111 fledglings.

Figure 7.9 Fledglings that eventually go on to become breeders are heavier than their counterparts whose fate is unknown. These data are from 11 fledglings that became breeders and 156 fledglings of unknown fate.

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Sex ratios – boy, girl? The last sections have described, among other factors, that Laughing Kookaburra mothers are able to manipulate the sex of the eggs they lay. In the context of siblicide, they do this to finetune the competitive environment within their brood. But these are not the only circumstances under which kookaburras manipulate the sex ratio of chicks in their broods. In fact, they have one of the most complex systems of allocating sex to their offspring known from any bird species, because breeding females also respond to the size and composition of their group. There are three major effects (Figure 7.10): ●

●

Simple pairs without any helpers produce more daughters than sons in their broods. This is probably because they live on the smallest territories, and resources might not cope with an increase in group size. Daughters, unlike sons, are far more likely to disperse before the next breeding season (Chapter 4), and therefore they will put less strain on the territory. Groups with helpers that are all male also produce female-biased broods; as with simple pairs, this could be because the territory has reached saturation point with a full complement of philopatric sons, and in this situation it is best to swing the sex ratio towards the dispersing sex.

Figure 7.10 The sex ratio of the clutch (for 66 clutches), and the brood at fledging (for 82 broods), for kookaburra groups of different composition. Breeding pairs without any helpers, and pairs with male-only helpers, have female-biased clutches and broods. If a group has female helpers, especially if all the helpers are female, the clutch and brood are malebiased.

Figure 7.11 The sex ratio of chicks depends on their hatch rank, and what sort of group they are hatched in to. The most extreme sex ratios are for the firsthatched chick in groups with all-female helpers (the chicks are always male), and the second-hatched chick in breeding pairs without helpers (the chicks are nearly always female). These data are from 86 broods.

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Groups containing female helpers, especially if all the helpers are female, had broods with more sons than daughters. There is probably a non-resource-based explanation for this pattern. Chapter 6 showed that female helpers have a negative effect on a group’s breeding success, because they are poor nest-provisioners and the other group members do not compensate for this properly. Consequently, a breeding female should avoid overburdening herself with too many daughters, or else she will pay a penalty the next time she breeds. Individual females respond facultatively each year to changes in the number and sex of their helpers. If one year they have three male helpers they are very likely to produce a female-biased brood. However, the following year they could have two female helpers and a single male helper, in which case they are very likely to switch and produce a male-biased brood. So far, the sex ratios mentioned have referred to the overall average for the brood (up to three nestlings). But the story gets even more complicated, because the sexes within a brood are not random – they are ordered. Remember that the eggs are laid and hatch in a sequence; across all nests about two-thirds of the first-laid eggs are male, about two-thirds of the second-laid egg are female, and the third chick is as likely to be one sex as the other. Because each group varies in the number and sex of helpers, imposing overall brood sex ratio biases onto these order effects results in very complicated patterns. Figure 7.11 shows that the sex of a chick depends on whether it was laid first, second or third and whether the attending group has male helpers, female helpers, both males and females, or no helpers. The most extreme sex ratios biases are for the first-laid eggs in groups with all female helpers – in the sample shown here, all these eggs turned out to be males. In contrast, the second-laid egg of simple pairs (i.e. no helpers) was almost always female. The physiological basis for this control is a mystery. However, the ‘responsibility’ for these complex sex ratio patterns probably lies with the mother rather than the father. Unlike mammals, in birds the females are the heterogametic sex. In other words, individuals with two different sex chromosomes (called Z and W in the case of birds, rather than the mammalian X and Y) will be female, and those with two Z chromosomes will be male. Therefore, whereas in mammals the sex chromosome in the sperm determines the sex of the embryo, in birds it is the sex chromosome in the egg. Somehow, then, the mother controls the sex of the eggs that she ovulates sequentially. ●

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Evolutionary biologists have predicted that animals should control the sex ratio of their young in an adaptive way, but the evidence for this in birds has only begun accumulating in recent years, mainly due the advances made in forensic genetic technology. Chicks are rarely dimorphic, making assigning their sex from appearance or even measurements impossible. Now, from a tiny blood sample taken from the newly hatched young, we are able to identify the sex of that individual quickly and accurately.

8 Mortality

A

n untimely death can end the reproductive dreams and foraging fantasies of animals at any stage during their lives, and kookaburras are no exception. There are two major periods of mortality in kookaburras – when they are in the nest, and when they are dispersing away from their natal group. The extent and cause of mortality in the nest was described in detail in Chapter 5 (pages 75–78). In three separate studies on the two kookaburra species, just under half of all the eggs laid resulted in independent offspring. This chapter summarises the rates and cause of mortality in adult kookaburras. Dispersal is a notoriously risky time for most animals, when they foray into unfamiliar areas, meet unfriendly conspecifics, bump into new predators, and struggle to find the best foraging sites. But a kookaburra helper’s only chance of reproducing is to disperse into a breeding position in another group. This means that most birds will be forced to run the gauntlet at some stage. Table 8.1 summaries the recruitment and mortality rates for Laughing Kookaburras around Canberra. Each year a third of all helpers disappeared from their groups. Although their fate is unknown, if we assume the population is stable then the number of those dispersers that attained a breeding position is about the same as the number of unbanded helpers that dispersed into the study area to take up breeding positions (16%). Since helpers neither float indefinitely nor become helpers in another group, we can assume that the remainder died (i.e. about 17%).

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The disappearance rate of helpers in their first year was similar to that of helpers in their second year (32%, n = 94, and 33%, n = 40, respectively). Although Laughing Kookaburras sometimes breed when only one year of age, the proportion of new breeders that were yearlings is very small (about onetenth of all new breeders are this young), so most of the kookaburras that disappear in their first year probably die. This is mirrored in the small data set available from the Dandenongs, where half of the independent young died before reaching their first birthday. Table 8.1 Recruitment and mortality of helping and breeding Laughing Kookaburras in Canberra. Annual adult recruitment and mortality

Percentage

Sample

Average annual adult mortality

11%

Mean of 146 birds per year

Helpers that become breeders each year

16%


Helpers that disappear each year (disperse or die)

33%


Average no. helpers that die each year

17%

Breeders that die each year

7%


Compared to helpers, adults that had become established as breeders had a much lower annual mortality rate (7%). In part this reflects the stable and risk-free conditions they live in compared with dispersing birds. However, since competition for breeding vacancies is likely to be fierce, these individuals may well be ‘better quality’ birds anyway, which could contribute to their greater survivorship. Combining the data for helpers and breeding birds gives an average annual mortality of just over 11%. This means that after 10 years, just under one-third (about 30%) of the birds present at the start of the 10year period would still be present; after 20 years, only 9% of the original birds would still be alive. If we calculate the life spans of a hundred birds over a 20year period using this annual mortality rate, the average life span would be around 12.5 years.

Sex-biased mortality Female Laughing Kookaburras suffer higher rates of mortality than males after they have fledged. At the Canberra study site, the fledging sex ratio was even (46% male in 82 broods). There was an indication that more female fledglings died before reaching independence at two months, but by the end of the juvenile stage and beyond the sex ratio is heavily skewed towards males. Over four years, the average sex ratio of helpers was 78% male. Female

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‘disappearance’ rates are higher than that for males in both the first and second year of life. For example, whereas 21% of male juveniles had disappeared before their first birthday, twice the proportion (43%) of their female counterparts had done so. This sex-biased mortality may occur because female kookaburras are larger than males, which means they need to garner more food simply to keep alive. When prey gets scarce, the larger females, especially those that are relatively young and inexperienced, are likely to succumb first. Blue-winged Kookaburra females are also larger than males, and by a similar extent. Despite living in a different habitat and climate than the Laughing Kookaburras, they show a similar bias in the helper sex ratio, to the tune of 85% male, strongly suggesting a similar sex-biased mortality. Besides coping with a larger body, breeding females also perform the overnight incubation and brooding duties, and this may expose them to higher predation risks from, for example, nocturnally hunting pythons.

Causes of mortality Adult birds die for various reasons including predation by a variety of other animals including various owls and diurnal raptors (e.g. whistling kites), but also quolls, goannas, pythons, cats and foxes. In the tropics, Blue-winged Kookaburras are especially susceptible to Rufous Owls and Red Goshawks. By weight, Blue-winged Kookaburras make up 17% of the diet of Red Goshawks. Adult kookaburras also die from starvation (especially during winter), and more rarely, through injuries sustained while fighting. An anthropogenic effect that can be quite severe in some areas is collisions with cars – kookaburras are not the fastest of fliers and their reflexes can be a little tardy. This is true for both Laughing and Blue-winged Kookaburras: six Blue-winged Kookaburras were killed in three months along 3 km stretch of road in the Northern Territory; this represented 13% of the local population. Another quite common human-related cause of death is drowning in steepsided pools and ponds – after a kookaburra dives into the water to bathe or pounce on a goldfish, it can be hard for it to clear the edge of the pool because it is a relatively heavy bird. Once trapped in the pool they quickly become waterlogged and soon drown. Some kookaburras are also killed by flying into windowpanes, and some birds that are overfed with inappropriate food in people’s backyards can suffer from nutritional defects. Rather than affecting the adults themselves, poor diet often causes problems to the developing chicks that the adults are feeding.

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9 Conservation and management

Both species of kookaburra in Australia are not in any immediate threat from catastrophic declines. They are widespread, inhabit a range of different habitats, and their behavioural flexibility means they adapt to habitat disturbance and fragmentation relatively better than many other species. However, on a local scale they face adverse effects from these processes just like any other species. Kookaburras rely on the presence of large tree hollows for breeding, and if this resource is unavailable (because of land-clearing) they will disappear from that area. Moreover, habitats can be modified in more subtle ways that have an equally dramatic effect. Competition from feral animals like honeybees, mynahs and starlings can soak up tree hollows. In addition, any perturbation that eliminates the big, old trees will reduce hollow availability for kookaburras as well as other hollow-users. For example, many towns have park and recreational areas with plenty of trees, but any limb that looks ready to drop off is cut off before it gets the chance, and any tree that looks hollowed-out is likely to be felled. In this age of litigation, councils and park authorities are understandably paranoid about these issues. However, this augurs poorly for native fauna that use tree hollows for nesting and roosting. As we ‘clean up’ woodland areas, we reduce their suitability for a range of animals. Kookaburras, being an easy-to-recognise hollow-user, are therefore a useful indicator of the health of a woodland.


Geoff Dabb

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Kookaburras adapt to landscape modification by humans better than many other species of bird.

The severe and ongoing fragmentation of woodland areas in Australia is now recognised as a major conservation issue. Many species have already been affected negatively, showing population declines and local extinctions. Other species are likely to experience similar fates in the future due to the limited dispersal that occurs between isolated fragments. Over time, inbreeding could have negative effects, and stochastic population fluctuations (such as droughts that cause unusual levels of mortality) will be impossible to recover from. Many of Australia’s woodland birds, like the kookaburra, have complex social systems that include restricted dispersal options; this tends to make them even more vulnerable to the effects of fragmentation. Having said that, kookaburras may be able to cope with a limited amount of fragmentation, as long as the fragments are not too distant from each other. For example, a study near Tumut in NSW examined whether Laughing Kookaburras were able to occupy eucalypt patches of different sizes (0.4–40.5 ha) embedded in a 5050 ha pine plantation, which is a very poor quality habitat for kookaburras. The kookaburras were apparently able to use quite small patches of eucalypts, many of which were too small to support a single territory. Although we do not know the required territory size of kookaburras in this area, the average territory size of Laughing Kookaburra groups around Canberra was 69 ha (range 16–224 ha), which is greater than the biggest eucalypt patch in the Tumut study. Being large birds, they were probably able to fly

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between a network of patches that were each too small to contain a single territory. This may have been possible because many of the eucalypt patches are only a few hundred metres apart, and at least they have a forest structure (i.e. pine trees) connecting them. This is not true of the small patches of woodland that persist in intensive farmlands, and kookaburras may be more reluctant to cover large expanses of open ground. Because they are amenable to suburbanisation and can become relatively tame, in places where humans feed them excessively like picnic areas and backyards kookaburras can become a nuisance, stealing food off barbeques and from picnickers’ fingers. Supplementary feeding sometimes brings more than one group into the area, which could have a knock-on effect on the local abundance of prey if the kookaburras eye off the odd skink or invertebrate in between the meatball morsels. People who like to feed wildlife need to keep a reasonable balance in mind – enough food to bring the animals in, but not so much that the animals become a nuisance or dependent on the supplementary food. Moreover, because steak pieces and sausages can never replace a natural diet, it is probably safer not to feed kookaburras while they are breeding, to avoid causing nutritional deficiencies in the young. At present, it is unclear whether the introduced populations of Laughing Kookaburras in Western Australia, Tasmania, Flinders and Kangaroo Islands and the Harauki Gulf of New Zealand (see Chapter 2) are having an adverse effect on other fauna. Over the hundred years since the introductions, there is no evidence that they have caused declines in any of their prey, nor for outcompeting other indigenous hollow-users. Concerns are sometimes raised, particularly in Tasmania, about their predatory impact on small bird populations. However, these concerns have all been raised in unsubstantiated anecdotal reports, and given that all dietary studies of kookaburras have shown that eggs, chicks and adult birds make up a tiny proportion of their menu, it seems unlikely that this would be generally different in the introduced populations. More data are required to understand the impact of introduced kookaburras, but at this stage eradication programs are probably unnecessary. Although we may have ‘got away with it’ in the case of kookaburras, the zeal of past acclimatisation societies for moving animals and plants all over the world was, with the benefit of hindsight, terribly misguided. Their legacy is a host of feral weeds and pests that have caused declines and even extinctions in our native fauna, and innumerable headaches for farmers. It is worth bearing this lesson in mind, as we continue to import plants for agriculture, various invertebrate pests for biological control, pet fish to adorn our aquaria and exotic birds for our aviaries, some of which undoubtedly have the potential to become significant problems.

References Chapter 1 Anon. (c. 1871). The young Australian’s alphabet. (W. Calvert, Melbourne.) Anon. (1927). Crimes of the kookaburra. Emu 26, 229–230. Berg, J. Jacko, the broadcasting kookaburra. Accessed 4 April 2003, . Burnside, J. A bit about words. Accessed 4 April 2003, . Campbell, A.G. (1927). Kookaburra as raider. Emu 26, 312–313. Carmichael, B. Koockard (Goanna). Australian Museum Online; Indigenous Australia. Accessed 3 April 2003, . Cawthorne, W.A. (1988). Who killed Cockatoo? (Margaret Hamilton Books Pty Ltd, Sydney.) Cozzolino, M. (2000). Symbols of Australia. 20th anniversary edition. (Penguin Books Australia, Melbourne.) Chisholm, A.H. (1965). Bird wonders of Australia. 6th edition. (Angus & Robertson, Melbourne.) CSIRO Division of Wildlife Research. (1969). An index of Australian bird names. Technical Paper No. 20. (CSIRO Publishing.) Dickinson, D. (1927). Notes on the kookaburra. Emu 27, 119–120. Dixon, R.M.W., Ramson, W.S. & Thomas, M. (1990). Australian Aboriginal words in English: their origin and meaning. (Oxford University Press, Melbourne.) Eden, C.H. (1872). My wife and I in Queensland. Longmans, (Green and Co., London.) Gould, J. (1848). The birds of Australia. (J. Gould, London.) Hooper, T. & Hooper, J. (1982). The laughing Australian. (Thomas Nelson Australia, Melbourne.) Kowanyama Aboriginal Community Council. Oykangand and Olkola dictionary. Accessed 2 July 2003, . Langloh Parker, K. (1896). Australian legendary tales. (Melville, Mullen & Slade, Melbourne.) Leckie, M.C. (1908). Brown kingfisher and snake. Emu 7, 155. Lumholtz, C. (1890). Among cannibals: an account of four years travel in Australia. (E.A. Petherick, Melbourne.) McCulloch, E.M. (1973). Kookaburras in literature and design. Victorian Naturalist 90, 84–89. Meredith, L.A. (1878). Grandmamma’s verse-book for young Australians. (W. Fletcher, Orford, Tasmania.) Mills, F.J.T.T. (193-?). Jack Sundowner. A day in the life of a kookaburra. (W. K. Thomas, Adelaide.) Morris, E.E. (1898). A dictionary of Australian words, phrases and usages. (Macmillan, London.)

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Morrison, P.C. (1967). Obituary for a kookaburra. In Birds of paradox. (Ed. J Pollard.) pp. 197–198. (Lansdowne Press, Melbourne.) Morrison, W.F. (1888). The Aldine centennial history of New South Wales. Vol. 1. (Aldine Publishing Co., Sydney.) Nathan, D. (Ed.). Aboriginal languages of Australia. Accessed 2 July 2003, . Nicholls, B. (1933). Jacko – the broadcasting kookaburra. (Angus & Robertson Ltd, Sydney.) Peterson, A. (2001). The call of the kookaburra. The Radio Heritage Collection. Accessed 5 April 2003, . Reed, A.W. (1998). Aboriginal fables and legendary tales. (Reed New Holland, Sydney.) Ryan, J.T. (1919). The kookaburra. Emu 28, 299–300. Timbery, L. Timbery tales. Bidjigal Co. online. Accessed 4 April 2003, . Wall, D. (2000). The complete adventures of Blinky Bill. (Angus & Robertson, Sydney.) Wesson, S. (2001). Aboriginal flora and fauna names of Victoria: as extracted from early surveyors’ reports. (Victorian Aboriginal Corporation for Languages, Melbourne.)

Chapter 2 Anon. (1903). Notes and notices. Emu 2, 159. Bartlett, A. (1948). Flinders Chase, Kangaroo Island. South Australian Ornithologist 18, 76–77. Christidis, L. & Boles, W.E. (1994). The taxonomy and species of birds of Australia and its territories. RAOU Monograph 2. (RAOU, Melbourne.) Condon, H.T. (1948). Birds introduced onto Kangaroo Island. South Australian Ornithologist 18, 78. del Hoyo, J., Elliot, A. & Sargatal, S. (2001). Handbook of the birds of the world. Vol. 6: Mousebirds to Hornbills. (Lynx Edicions, Barcelona.) Fletcher, J. (1907). Great Brown Kingfisher (Dacelo gigas) in Tasmania. Emu 7, 119. Fry, C.H., Fry, K. & Harris, A. (1992). Kingfishers, bee-eaters and rollers. (Christopher Helm, London.) Higgins, P.J. (Ed.). (1999). Handbook of Australian, New Zealand, and Antarctic birds. Vol. 4: parrots to dollarbirds. (Oxford University Press, Melbourne.) Jenkins, C. (1977). The Noah’s Ark syndrome. (The Zoological Gardens Board, Perth, WA.) Jenkins, C.F.H. (1959). Introduced birds in Western Australia. Emu 59, 201–207. Lever, C. (1992). They dined on eland. (Quiller Press, London.) Long, J. (1981). Introduced birds of the world. (Reed, Sydney.) Lysaght, A. (1956). Why did Sonnerat record the kookaburra, Dacelo gigas (Boddaert) from New Guinea? Emu 56, 224–225. Lysaght, A. (1957). The first specimens of Dacelo novaeguineae and D. leachii in European collections. Emu 57, 209–210. Mathews, G.M. (1926). An important date. Emu 26, 148.

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Mees, G.F. (1977). The scientific name of the laughing kookaburra: Dacelo gigas (Boddaert) v. Dacelo novaeguineae (Hermann). Emu 77, 35–36. Thomson, G. (1922). The naturalisation of animals and plants in New Zealand. (Cambridge University Press, Cambridge.) Vigors, N.A. & Horsfield, T. (1827). A description of the Australian birds in the collection of the Linnean Society, with an attempt at arranging them according to their natural affinities. Transactions of the Linnean Society of London 15, 170–331.

Chapter 3 Batey, I.(1910). Birds about Drovin, Gippsland. Emu 9, 241–245. Curl, D. (1999). Behavioural ecology of the Blue-winged Kookaburra and other kingfishers. (Monash University, Melbourne.) Higgins, P.J. (Ed.). (1999). Handbook of Australian, New Zealand, and Antarctic birds. Vol. 4: parrots to dollarbirds. (Oxford University Press, Melbourne.) Iwaniuk, A. (2003). The evolution of brain size and structure in birds. (Monash University, Clayton.) Mattingley, A. (1902). Jackasses at shooting matches. Emu 2, 108. Moroney, M.K. & Pettigrew, J.D. (1987). Some observations on the visual optics of kingfishers (Aves, Coraciiformes, Alcedinidae). Journal of Comparative Physiology 160, 137–149. O’Grady, D. (1961). Australian Bird Watcher 1, 144. Parry, V. (1968). Sociality, territoriality and breeding biology of the Kookaburra, Dacelo gigas (Boddaert). (Monash University, Clayton, Victoria.) Pettigrew, J.D. (1979). Binocular visual processing in the owl’s telencephalon. Proceedings of the Royal Society of London Series B-Biological Sciences 204, 435–454. Pettigrew, J.D. (1991). Evolution of binocular vision. In Vision and Visual Dysfunction, Volume 2: Evolution of the Eye and Visual System. (Eds J.R. Cronly-Dillon & R.L. Gregory.) (MacMillan Press, New York, 271–283.)

Chapter 4 Legge, S. & Cockburn, A. (2000). Social and mating system of cooperatively breeding laughing kookaburras (Dacelo novaeguineae). Behavioral Ecology and Sociobiology 47, 220–229. Parry, V. (1973). The auxiliary social system and its effect on territory and breeding in kookaburras. Emu 73, 81–100.

Chapter 5 Curl, D. (1999). Behavioural ecology of the Blue-winged Kookaburra and other kingfishers. (Monash University, Melbourne.) Legge, S. (2000). The effect of helpers on reproductive success in the laughing kookaburra. Journal of Animal Ecology 69, 714–724. Parry, V. (1968). Sociality, territoriality and breeding biology of the Kookaburra, Dacelo gigas (Boddaert). (Monash University, Clayton, Victoria.)

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Parry, V. (1973). The auxiliary social system and its effect on territory and breeding in kookaburras. Emu 73, 81–100. Thomson, D. (1935). Some adaptations for the disposal of faeces. The hygiene of the nest in Australian birds. Proceedings of the Zoological Society of London 1934–35, 701–707.

Chapter 6 Curl, D. (1999). Behavioural ecology of the Blue-winged Kookaburra and other kingfishers. (Monash University, Melbourne.) Legge, S. (2000). The effect of helpers on reproductive success in the laughing kookaburra. Journal of Animal Ecology 69, 714–724. Legge, S. (2000). Helper contributions in the cooperatively-breeding laughing kookaburra: feeding young is no laughing matter. Animal Behaviour 59, 1009–1018. Parry, V. (1968). Sociality, territoriality and breeding biology of the Kookaburra, Dacelo gigas (Boddaert). (Monash University, Clayton, Victoria.) Parry, V. (1973). The auxiliary social system and its effect on territory and breeding in kookaburras. Emu 73, 81–100.

Chapter 7 Griffiths, R., Double, M.C., Orr, K. & Dawson, R.J.G. (1998). A simple DNA test to sex most birds. Molecular Ecology 7, 1071–1075. Legge, S. (2000). Siblicide in the cooperatively breeding laughing kookaburra. Behavioural Ecology and Sociobiology 48, 293–302. Legge, S. (2002). Siblicide, starvation and nestling growth in the laughing kookaburra. Journal of Avian Biology 33, 159–166. Legge, S., Heinsohn, R., Double, M., Griffiths, R. & Cockburn, A. (2001). Complex sex allocation in the laughing kookaburra. Behavioral Ecology 12, 524–533. Nathan, A., Legge, S. & Cockburn, A. (2001). Nestling aggression in broods of a siblicidal kingfisher, the laughing kookaburra. Behavioral Ecology 12, 716–725.

Chapter 8 Curl, D. (1999) Behavioural ecology of the Blue-winged Kookaburra and other kingfishers. (Monash University, Melbourne.) Hobbs, J.N. (1966). Whistling kites taking a kookaburra. Emu 77, 46. Legge, S. & Cockburn, A. (2000). Social and mating system of cooperatively breeding laughing kookaburras (Dacelo novaeguineae). Behavioral Ecology and Sociobiology 47, 220–229. Parry, V. (1968). Sociality, territoriality and breeding biology of the Kookaburra, Dacelo gigas (Boddaert). (Monash University, Clayton, Victoria.)

Chapter 9 Lindenmayer, D.B., McCarthy, M.A., Possingham, H.P. & Legge, S. (2001). A simple landscape-scale test of a spatially explicit population model – patch occupancy in fragmented south-eastern Australian forests. Oikos 92, 445–458. Parry, V. (1968). Sociality, territoriality and breeding biology of the Kookaburra, Dacelo gigas (Boddaert). (Monash University, Clayton, Victoria.)

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Kookaburra: king of the bush

Children Of The Bush

Pat Of Silver Bush

Pat of Silver Bush

Pat of Silver Bush

Beating Around the Bush

The Bush Betrayal

The Burning Bush

Considering the Bush Presidency

The Bush Betrayal

Tales for the Bush

The Faith of George W. Bush

Bush Doctor

Manhood in Hollywood from Bush to Bush

In Defense of the Bush Doctrine

The King of Torts

The King of Torts

King of the Corner

The King of Torts

The King of Torts

The King of Clayfield

The King of Dreams

The King of Nothing

the King Of Torts

The King of Plagues

The King of Nothing

The King Of Lies

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