Little Book of Monitor Lizards: A Guide to the Monitor Lizards of the World and Their Care in Captivity

A

LITTLE

BOOK

OF

MONITOR

LIZARDS

A Guide to the Monitor Lizards ojthe World and their Care in Captivity

~-

,~-

-\:­

< •.

i.

by Daniel Bennett

In Memory of Patrick Joseph Price 1958- 1988

Many people helped me with this work, directly or indirectly.

I refrain from naming them in order not to embarrass anyone. Their

help, enthusiasm and hospitality are cherished and appreciated.

Special thanks must go to my mother, without whom

nothing would be possible

First published in 1995

© Daniel Bennett 1995

All righls reserved . No pan of this publication Lnay be reproduced, slored ill a

reuieval system or transmiued in any ronn or by any means, electronic,

pholocopying , recording or otherwise withoul the wrillen pennission

of the copyrighl holder. Every carc has been laken in the compilalion

of Ihis book. but the publisher can assume no responsibility for any errors

or omissions , or any effeclS arising therefrom.

Brilisb Library CalaJoguing in Publicalion Dala. A calaiogue record

for this book is available from the British Library .

ISBN: 095266320 1

Published by:

Viper Press,

P.O. Box 10087,

Aberdeen AB2 2GJ ,

Great Britain.

A large font version of this text is available from the publishers on request.

CONTENTS; I. AN INTRODUCTION TO THE FAMILY V ARANIDAE............ ................ ..

................7

2. THE HISTORY OF MONITOR LIZARDS.

Extinct monitors ..... .................... ..... .. .. .................... ......................... .. .............. ...... ..... .. ... ... ........ . Living monitors...................................................................................................................... .

.. .. 10

14

3. THE INSIDES AND OUTSIDES OF MONITOR LIZARDS

Metabolism ..................... ................... ........................... ........... ......... ..... ............ ........... .. .........

Heal......................... .......................................................................................................................

. ........... I 7

....... 19

Water .... .. ................... ....... ... ... .... ... ....... ... ..... .... ....... ................. .. .... ....... ............. ................... ........... ........... 20

Smell & tasle............ .............................. .............. ............... """ .. " .... ,, .. "" .......... " ........ "." .... " ..... " .... .. "".21

Sight ................................ " .. .... ......... ... ................ " .... ...... .......... ...... .. .. ....................................................... 23

Hearing ......................... .. .. ........ ............. .. ...... .. ........ ...... . " ................. .. ..... ........... ............................ .......... 23

Touch.... ..... ............ ... .................................. ............... ... ............ .. ....... .. ............................... ......................... 24

Size...... .. ...................................................................................................................................................... 24

Teeth & skull ...... ..... .......................... .. ....... ....... ........ ..... .......... ....... ................. ............... ....................... ...25

Noslri Is ........... ....... .............. , .............. ........ .................... ................... .................. ....... ..... .......................... 2 X

Feet & daws.............. .. ........ ............. ....................... ................... .. ................ ... ...... ....... ......................... .... 2X

Tails..................................................................................................................... .... .............. ...................... 30

................11

Colour & panern ............................................................... .................. ....... .............. .. . . 4. THE LIFESTYLES OF MONITOR LIZARDS.

......................... ......................... .. .....11

Defence.................................................................... . 14

Movement and shelter ................................ .. ............ .. ...................................... 36

Feeding.... .............. ... .................... ..... ..... .... ..... .... ........................ .... . Soci:~ behaviour. ..... .... .......................... ............... .......... .. .................... . . ................................... .4U

Reproduction ... .. .. ............... ................... .......................... ................... .. . .................... ..................... .. ....,4U

5. THE MONITOR LIZARD AND MAN.

Monitors in folklore and an.............................................................................. ......... .. ... ........................... .47

Uses of monitors by man ............................. ..... .. .............. ......................... .. .. .. .......... .... ......... .... ................ ..49

Use of man by monilOrs ........... ....... .. .......... ............... .... ... ...... ............ ........................... .. ........................ ..... 53

6. THE MONITOR LIZARDS OF THE WORLD:

Varallus acanthurus ............................................. ............ ............................. .................... .......................... 54

Varanus albigl/laris ............................................ .................. ................................................................... .... 56

Varanus buritji ............................................................................................................................................. 59

Varanus bercurii .................................................................................................. ....................................... 59

Varallus bengalensis ................................................. ........................................ ............ .. ................... .. ....... 60

VarCl/tus bagerti.................................................. ......................................................................................... 64

Vara/tus hreviwuda.............................................................................................................. .... 64

Varanus mudolinearus ................................................ ................................................ .... ............................ .65

Varanus doreanus .................................................................................... ................... .. .......................... ....66

Varanus dumerilii .................... ..... .................................................. ...... .................... .......... ....................... .. 66

Varallus aemius...................................................... ........... ........................... .. ................................ ........... 6X

Varallus exanthematicus ............................................................................................................................. .6'1

Varallus flaves' ·ells .......... ..................................................................................................... ....................... 72

Varallus flavirujus ... .... ..... ............. .... ............ ........... .... .......... ..... ......... ... .. ..... .... ....... ...75

Varanus giganteus ............................................................... ...... .... , .... ................... "'''''''''''' ...... ............... .MO

Varanus gilleni..... ... ........ ......... ........ ................ ....... ............................................................... X2

Varallus glauerri.................. ......... ....................... ... ............ ........ ... ................... ......... H1

Varanus glebopalma.............. ................. ........................................................................... ... X4

Varanus gouldii................................................................... ... ........ ................. ... "".. ""." .. "... ..X5

VurCl/IllS griseus.. ........... "" ....... " .. " .."............. ...... "".. ". " .. " ""XX

Vurufills illdif.'us . .. ...... ............ .

n,

I))

\ ! OJ'f1I1f1S

johi('nsis ........

... ....................... .... ...... ..... ...... ......... .... .. ... ....... ................. .98

\ : orOllftS

/.:ill!!or/tn'....

.. ........... .. ............................................................................99

\ 'O/,{l/IIiS

/.:tlmor/o(''' sis...... .

I '{I/tll/IIS Inl'rf('l/si "oraI1I1S nlifl·h ('/ Ii ...

.. ............................................................................................99



................ .... ........................................................ ........ .. ... 102

..... .. ..... ... . .. ...

.. .. .... ... ..... ... ...

....... .. ..............................

. ............. 104

........................................................ .. ......... 105

\'arUlIrt.fi ni/ofiells .

. ........................... ........ .. ........... 109

\:f/UUIIU ofin/l'(,lIs...

......................................... 112

VurOIllH /Ii/naf(,1I.fiis. .

. ................. .. ................................................... 112

Varun/iS "r(lsinus .. \I(I"(/IIf(.~ "/,i,,,orriills.

.. ........................................ ........................................................ 111

. ....... .. .................................................. ........ ... ........... 114

\'ol"al/us r(lS(,1I/)crRi .. Varul/us tluii('olli.'i....



....... ................

.......... ... ................................................. 116

.. ............................................................................................ 117

\'oral/ lts soh·orin,.;;

............ .......

1 /(J"(lllu.~ SU/\'(}lnf

.. .. .. .. .... ... ......... ........... .... ....... ..................... . . ........................ ..... . 119

. .................. .. ................. .. ................................................................................ 123

.. .. .... ... ..................... ....................... ...................... 124

.......................................... , ........................................................... 12.5

.., ................................... ....... ............... ............. ......... ....... ................ ...... .... 12.5

\/arU1IIIJ J((}/ariJ .... \ '"rO"IIJ J('m;r('m(' x. . \IOftl"IIS Jinli'iJ \ 'ora1lUS .fi/Jef/t·('f; ..

\'arunlls s(orr;............

. ... ............ .. ................... .... .. ....... , ....................... ........ ............... ................. 126

\'a l"U"UJ tclellcslcs ....... ............................................................................................................................. 127

\Jura"us fcrjue .. . ........ . ............................... .. ...... ................................................. 12R

VuruIIIIS lim(J,.e1f .~;s ........ ...... .. ..... ............................,........................................,......... .... ............................ 12R

"afolllls 'fiSI;S .. ..... .... ........... ....... .......................... ........ .... ..... .. " ............................................................... 129

\ ' arUlIll.f. \,ur;lt5

Varo""s ycmcnensi.ft ..

..................

.. ...................................................................................... 112

.. .................. .... ...... .............. ........ ....................................................... 134

7.KEEPING MONITORS IN CAPTIVITY.

Safety. .. .............................................................................................. ,................ ... 137

HD\lsing... . ... ... ....... ........... ........ ..........................,.......................................................... ....................... 142

Furnishings. ....... ............... .......................................................................................................... 145

Heat ................................................... ...................................................................................................... 14R

Light .......... .................................................. ......... .. ............................................................................ ....... 150

Water ...................................................... ......... ........... .............................................................................. 151

Diel ........................................................................................................................................................... 151

Disease ...................................................................................................................................................... 158

H. BREEDING MONITORS IN CAPllVITY.

Sexing MonilOrs ............................... ........ ................................................................................................. 161

Hnusing Monilors togelher ......................................................................................................................... 163

Triggering hreeding .............. ..... ..................... ............. ............... ........................................... .................... 163

Courtship and Maling ......... ....................................................................................................................... 164

Egg laying................................................................................................................................................... 165

Egg Incubation ........................................................................................................................................... 165

Carc of Ihe Ynun g...................................................................................................................................... 166

9. THE FUTURE FOR MONITOR LIZARDS ............................................................................................ 16R

APPENDIX I:GLOSSARY APPENDD< II: FURTIlER INFORMATION BihliogTilflhy Useful Socielies and Publications. APPENDIX 111: CLIMATIC DATA APPENDIX IV. CONVERSION TABLES APPENDIX V: CONSTRUCTION OF A SIMPLE CHIPBOARD ENCLOSURE

FOREWORU Monitor lizards are extremely exciting animals. Without doubt they look more like dinosaurs than any other living creatures. They are aggressive, carnivorous, intelligent reptiles and although some are true giants, others will fit easiJy into a matchbox. Large monitor lizards are found over almost a third of the Earth and so it seemed incredible to me that I could find so little written about them. With a lot of help from library staff I read as much literature as I could find about the monitor lizards. I tracked down the authors of much of the work and besieged them with questions. Then I visited and interrogated reptile breeders. Despite the naivete of many of my questions my requests were treated with great courtesy. The more I learned about monitor lizards however, the more I knew I didn't know. Some of the most important aspects of monitor lizard biology are still virtually unknown. Indeed , our knowledge of even the larger monitor is so incomplete that new species are still being discovered with regularity and virtually nothing is known about some of the commonest members of the family. This little book, therefore, is intended to be an introduction and guide to the wondrous variety of monitor lizards with emphasis on their ecology and care in captivity. The information has been provided by people who have worked and lived with monitor lizards. in the wild or in captivity. Much of it has been published before, but it is scattered widely through the literature and disguised in about half a dozen languages. With the exception of some minor articles of my own, to which I have given undue prominence, I have tried to omit any speculative material and have been obliged to ignore a lot of good information when the identification of the animal under discussion is in doubt. With the exception of proper names. I have tried to keep scientific terminology out of this book altogether and a glossary and conversion tables can be found at the back. In the last five years there has been an explosion of interest in the monitor lizards and this is reflected in the huge amounts of new literature, much of which is not covered in this volume. This little book of monitor lizards is designed to be a summary of our knowledge of these magnificent animals, both in the wild and in captivity, but it is by no means complete, nor does it claim, in any way, to be an authoritative work. It is to be hoped that in the near future some of the people who have had most success and experience with keeping monitor lizards will publish much more competent and thorough guides to their care in captivity. making mine memorable only for its modest price and more outrageous mistakes. Daniel Bennett Glossop. June 1995. Postscript Four months ago I underestimated the amount of recent literature published on monitor lizards. I have attempted to include as much of it as possible, as well as some papers that are not yet been published. but were very generously provided by the authors. As a consequence some minor typographical errors have been overlooked and remain in the text. I hope that readers will forgive me for them. D.B ., Aberdeen , September 191)5 .

5

INDEX OF COMMON NAMES Argu~ goanna s('(' V!!ollldii Asiatic w~ter monitor S(,('

Gillen's goanna see V.!?il/eni Glauert's goanna see

V .w/\'(/Ior

Vglollcrti

Banded tree goanna

S('('

Vsm/aris

Beccari's monitor sc(' Vh('c('ari

Bengal monitor S('(' V.l),.n!!a/rnsis

Black-headed goanna

,1'('('

Vlrislis

Black tree monitor ,1'('(' Vh{'( {'(/ri & V.ho!?('rti

Blue-nosed goanna

Vsemiremex

V.rudicollis

Kalabeck monitor see V.indicus & V.doreanus Karl Schmidt's monitor see

Blue-tailed monitor see

V.johieflSis.

Blackjungle monitor ,1'('('

V .eremilL~

Goanna X see V jlavimflL~ Racehorse goanna see Gould's goanna see V,gollldii V tristis , Vgouldii & V jlaviru,flls Rock leguaan see Gray's monitor ,I'('C Valhigularis Volivac(,lIs Rosenberg's goanna see Green tree monitor see V.rosenbergi Vprasi l!lL~ Rossellsland monitor see Grey Monitor S('C V.!?ris(,lLv V.telenestes Rough-necked monitor see Harlequin monitor see Vrudicollis Vrudicollis Rusty goanna see

,1'('1'

VI('riae

Pygmy desert goanna see

Salvadori's monitor see Vsalvadorii

Blunt-nosed goanna see

Sand goanna see V jlavirufus Kings' goanna see Vkin!?orum Savannah monitor see Komain monitor see Valbigularis &

VprimordilL~

Vsalvator

Vexanthematicus

Bos\.:'s monitor see

Komodo dragon see

Vexanthematicus

VkomodoeflSis

Sepik monitor see V.jobiensis Short-tailed goanna see

Vdormnus

Bogert's monitor ,1'1'1'

Koniecznyi's monitor see

V.brevicauda

Vho!!erti

V!?riseus koniecznyi

Spiny-tailed goanna see

Lace goanna see V.varius

Spotted tree goanna see

caSpilLv

Mangrove monitor see

Stripe-tailed goanna see

Clouded monitor see

VindiclLv

V.caudolineatus

V.hen!?a/ensi.~

Mertens' goanna see

Storr's goanna see V.storri

Bulliwallah sce V.mertensi

V.acanthurus

Caspian monitor ,1'1'(' V.!?riSl'lLV

neb,doslLV Crocodile monitor see V..w/vadarii Cuming's monitor see V..wlvator

V.similis

V.merteflSi

Mitchell's goanna see V .mi tchelli

Timor monitor see VtimoreflSis, V.scalaris &

I

Mournful goanna see V.tristis V.similis Mulga goanna see V.gil/eni Tree crocodile see

Desert monitor see V.griseus Dumeril's monitor see

Nameless goanna see

Vdumerilii

V jlavirufus

Tree leguaan see V.albi!?u/aris Twilight goanna see

Nile monitor see Vniloticus

V.glebapalma

V.salvadorii

Emerald monitor see VprasinlLv

lOra see V.komodoeflSis

Rute monitor sec Vrudicollis IPeaCh throated monitor see Freckled goanna see Vtristis V.jobieflSis Perentie see V!?i!?antelL~ Giant Goanna see Me!?a/ania Pilbara goanna see

I

l"i.H·O

Vpilharensis

1

An Introduction to the Family Varanidae

Monitors are a small but diverse group of lizards. They have been around for at least seventy million years, have probably lived on all of the Earth's continents and are still present in three of them . Monitor lizards are carnivorous and generally feed on any animals they are able to swallow. The family includes the largest lizards that have ever walked the Earth. But whilst some are gigantic creatures capable of preying on man, others are so small they have difficulty overpowering anything much larger than an grasshopper. Some of the largest lizards that ever walked the Earth still alive today . Most monitor lizards are only active during the day and all reproduce by laying eggs, but they employ a wide variety of reproductive strategies. The monitors show astonishing variation in size. diet, behaviour and habitat, and are a marvellous example of how one tiny group of animals have adapted to suit many different environments. The smallest monitor lizard reaches a total length of only 20 cm and a weight of less than O.OSkg (SOg). The heaviest monitor weighs as much as 2S0kg. The longest monitor lizard has a supposed total length of over 47Ocm. Monitor lizards inhabit areas which are among the driest and wettest places on Earth and are often present in large numbers. They are found in deserts. on seashores, in woodlands, grasslands, rivers, lakes, swamps and rainforests. Monitor lizards are extremely important to the economy of people, acting both as pest controllers and as a source of meat and leather. Some monitor lizards have been almost completely unaffected by the emergence of mankind (a few !)ave even benefited from it), but others have suffered extermination to the point that it is reasonable to suppose they will be have vanished from the wild before the end of the next century. Despite their size and their ecological and economic importance, the monitor lizards have not been given the attention they deserve by biologists. In recent years the siruation has improved greatly, but even now virtually nothing is known of the ecology of many species, including some of the largest ones. The purpose of this book is to surrunarise what is known about the way of life of monitor lizards in the wild, and how that knowledge may be applied to their captive propagation. Monitor lizard can be extremely rewarding animals to keep in captivity but, in my opinion. there is little point in keeping wild animals confined if they do not reproduce. The day may come when some of the monitor lizards will disappear for ever if they cannot be bred in captivity. Even small scale propagation of some species could make a significant contribution to their overall populations as well as providing important clues to their life history in nature. In the animal trade captive bred examples of even the commonest species are in great demand and fetch much higher prices than their wild counterparts, but they are all too seldom seen. For these reasons special emphasis has been put on the care of monitor lizards in captivity, and infonnation regarding their propagation is included wherever known. Again certain cases have been omitted either because they are suspect or impossible to verify and many more have been inadvertently overlooked. There is a wealth of unpublished data which would be of enonnous value to would-be varanid propagators. If you have experiences of keeping monitor lizards, good or bad, you should share them. Herpetologists are renown for being amongst the friendliest people in the world and herpetological societies provide an ideal way to meet, share ideas and learn from other enthusiasts. A list of some groups and societies with a special interest in monitor lizards is given at the end of the bibliography but is 7

Little Book of Monitor Lizards by no means comprehensive. Contacts for local societies can be found in magazines devoted to rertiles, or ask at a local zoo or museum.

NAMES ANn InENTIFICATION There are two explanations of the origin of the common name "monitor lizard", The Oxford English Dictionary attributes it to the belief that they gave warning of the vicinity of crowdiles. A more likely explanation is that the Arabic term for a lizard "ouaran" became l:onfused with the German verb "Warane" (to warn), hence the scientific name Varanus and the English term monitor (Lydekker in Stirling 1912). In parts of the world colonised by Europeans the monitors were confused with the large lizards of the Americas, the iguanas. Henl:e in Australia they are known as goannas. and in South Africa they are known as leguaans. Easy identification of monitors is hampered by two things; dramatic differences in the appearance of young vs. adults and geographical variations in colour and morphology, particularly in species which inhabit a wide range. Scientists often rely heavily on scale counts and characteristics to distinguish species. Unfortunately it is utterly impractical to count the scales of animals seen only at a distance, or those of captives, particularly of the very large and very small varieties. I have avoided detailing the scalation of the monitors except where no other characteristics will serve to distinguish species or subspecies. This information can be found in the literature cited . Keys to distinguish monitor species can be found in various works of Mertens (translations in Funk and Vilario 1980), Storr (1980, et aJ 1983) and Vernet ( 1(84). Difficult to spell and impossible to pronounce, scientific names are cumbersome and tongue­ twisting, but essential. Even today much information in the literature is wasted or misunderstood because of confusion over the identity of the creatures concerned. Scientific names are used as little as possible here, but their use is vital for correct identification of different species because common names (e.g. "water monitor") are often ambiguous. Monitor lizards belong to the family Varanidae. At present all living species belong to the genus Varanus and all other recognised genera are considered extinct. The generic narne Varanus is often abbreviated to V. and the specific name written in its entirety, e.g. V.tris/is. Between the generic name and the specific names a subgeneric narne may be inserted in brackets, e.g. Varanus (Odatria) tristis. After the specific name there may be a subspecific name, e.g. Varanus (Odo/ria) tristis orientalis. In some cases the subspecific name may eventually replace the specific name if the animals are thought different enough to warrant being recognised as separate species, e.g. Varanus (Odotria) orientalis. It is possible that the genus Varanus will be split into a number of smaller genera before the end of the century, because some people consider the present classification to be too simple. In this case the subgeneric name may replace the generic name, e.g. Odotria tristis orientafis or even Odatria orientalis. The name is followed by the author and date of the animals' original description, in which he or she nominated a single, pickled, lizard as a typical example of the race. This unfortunate creature is known as the holotype. In the past many people have named animals without being aware of previous descriptions of the same species. In this case the name of the oldest existing holotype is given priority. Many monitor lizards have been renamed. or even unnamed, in recent years. In addition many monitor species remain undescribed. A useful list of poorly-known monitors and unknown species can be found in Philippen (1995).

8

Introduction

Where scientific names are completely useless is in the areas where the lizards actually live. For example, a monitor lizard from Africa is known as eikwambo, mbulu, gruza, awonriwan, kgwate, uxamu, mampan-tintin and at least a hundred other names, but very few of the people who are acquainted with it in nature are aware of Linnaeus' description of the species in 1758 and the subsequent revisions that led to the name Varanus niJolicus. This is unfortunate for us, for they are the people who know most about it and can contribute best to our knowledge of its natural history. Much can be learned about the ecology of monitor Lizards even on a family holiday, by questioning knowledgeable locals. Knowing the local name for the animal you are interested in and having a good clear photograph of it are essential to avoid misunderstandings. They will probably be happy to show you the animals living wild and give you the most memorable moments of your holiday. As our understanding grows, so does our respect for those with whom we share the planet.,; who were here long before us and may be here long after.

.,~,

,

iI"

.•~·.')?f

'J",

t

Opposite: Bipedal ritual combat in a large monitor (M'], Bennen after Tsellarius 1994). Above: Ritual combat in a dwarf monitor (M .J ,Bennen after Carpenter el at 1976),

39

Monitor Lizards of the World

SOCIAL BEHAVIOUR Monitor lizards are not usually sociable animals. Congregations of monitor lizards have been reponed amongst juveniles, around carrion and on riverbanks but most are solitary creatures that shun company except during the breeding season. They are not territorial in any strict sense and the activity areas of many animals may overlap. However most have activity ranges that are large enough to make accidental encounters unlilcely, The lizards are certainly able to detect the presence of other monitors by the smells they leave behind them. Quite often, when two monitor lizards meet one will attempt to eat the other. They are well equipped to deliver savage bites and grievous scratches and so every encounter is potentially dangerous. When face to face with each , other monitor lizards engage in a series of distinctive behaviours, so me of wh.ich are h.ighly ritualised (e.g. Auffenberg 1978, Daltry 1991). All involve a series of visual and probably scent oriented cues and they playa very important role in preventing the lizards' social occasions from degenerating into a cannibalistic orgy. Rirualised fights have been recorded for many species of monitor lizard (e.g. Ali 1944, Deraniyagala 1958a, Murphy & Mitchell 1974, Carpenter el al 1976, Auffenberg 198Ia&b, 1988, Tsellarius 1994 and particularly Hom 1985 & Hom el al 1994). The most dramatic are those of the larger species in wh.ich the animals stand bipedally, gripping their opponents around the shoulders and attempt to wrestle each other to the ground. In dwarf monitors and some larger species the wrestling matches only occur in a horizontal position, with the lizards grasping each other with all four legs and sometimes supporting themselves only with their head s and tails. Again the object is to overpower and get on top of the opponent. In all cases these ritualised fights allow the lizards to test their strength against each other without incurring serious injuries, particularly bites. Only rarely does one lizard break the rules and tear the other to pieces. Success in combat seems to be determined largely by strength and the winners tend to be the heavier animals, at least in bipedal contests. The fights are often presumed to occur only between males but there is evidence that they are practised by both sexes (Gaulke 1992a, Hom el al 1994). However males appear to engage in engage in ritual combat more often, as is evidenced by the large numbers of scars on the backs of old specimens. In the wild the fights are often observed to occur around carrion and are most common during the breeding season. Once dominance has been established the losers may avoid having to fight rematches by displaying appeasing behaviours when they encounter the dominant animal (Auffenberg 1981 , Daltry 1991). It is presumed that animals which habitually win in bouts of combat have access to better resources (food, she lter, basking sites, nest si tes) than the losers, and that amongst males, the dominant animals would be more likely to be successful with female s, although this is not always the case (Carter 1990).

REPRODUCTION. All monitors reproduce by laying eggs and usually viable eggs are produced only within two months of mating. Observations in captivity (Card 1993, Eidenmuller 1993) suggest that in some cases sperm storage of up to three months is possible. In many species mating and egglaying occurs only during a few month s of the year but in some tropica l species the breeding season is extended and may continue throughout the year. Very few studies of free­ living monitors have been able to gather much infonnation about reproduction but a great deal of data is being accumulated for captives (see Hom & Visser 1990, 1991 for reviews). Plior to mating the female must expend a great deal of energy in the production of eggs. The male uses a comparatively minuscule amount of e nergy making spenn. For this reason females are usually less active than males, grow at slower rates and achieve smaller s izes. The 40

Lifestyles of Monitors number and size of the eggs produced varies enormously between species. Some produce clutches of eggs that weigh almost half of their body weight. The eggs take up so much space in the body cavity that the female may be unable to feed whilst heavily gravid. Clutch size and relative mass vary greatly between species. Some large monitors lay comparatively light clutches whilst some small species produce what appears to be an impossibly huge clutch. The most prolific species are the African white-throated, Nile, and Bosc's monitors, all of which lay large numbers of eggs which hatch quickly into small offspring, each with very little chance of survival to adulthood. Other large monitors produce small clutches of eggs that may require longer incubation and hatch into much larger offspring. Even among dwarf monitors clutch size varies by several magnitudes. Females may accumulate the energy used for egg production as fat whilst food is abundant and make the eggs during periods of relative inactivity. In other species egg production does not appear to rely on large fat reserves. Whether a monitor can make a full clutch of eggs depends on the amount of energy she can afford to invest in them. Observations in captivity have shown that many monitor lizards are capable of producing more than one clutch of eggs per year if they have unlimited food resources. In most cases two clutches of eggs are produced in quick succession but some monitors may produce a clutch of eggs every three months. Some can produce their own body weight of eggs in a year, but it is doubtful that free-living individuals ever have life so good. The methods currently used to investigate the reproductive biology of monitor lizards in the wild require that the animals be killed and so there is no evidence that multiple clutching occurs in the wild, but it certainly occurs wherever suitable food and climate exist. Having produced a clutch of eggs at great expense, the female needs some good quality sperm to fertilise them. She indicates her sexual receptiveness by releasing scent signals which may be detected by a large number of males. But the males, literally bursting with sperm, flfSt seek out other males and engage in the bizarre contests of strength which seem to detennine their likelihood of achieving successful copulation. The amount of energy female monitor lizards must expend to produce young with a good chance of survival forces them to live relatively sedentary lives during at least part of the year. It is clearly in her interests to have them fathered by the most desirable male available. From her point of view a desirable mate is a big, strong one. Monitor lizards, as we have seen, are very well equipped for killing other animals and often practise cannibalism. Therefore in their social interactions with other monitors they must adopt very different behaviours than those employed in the quest for food . The riTUal combat practised by monitor lizards permits a hierarchy to be established without continual fighting. Similarly courtship in monitor lizards, although less riTUalised, reduces the chances of serious injury or death when investigating possible mates. Detailed accounts of courtship and mating can be found in Auffenberg (198Ia&b, 1988), Moehn (1984), Carter (1990), and Green & King (1993). In some species the female tends to be the dominant partner and only males strong enough to completely irrunobilise her are able to achieve copulation. In some species the act of love is performed very gently, but in others it is accompanied by a great deal of biting and scratching. Some accounts of mating could be interpreted as rape. Actual copulation is very short in some species and protracted in others, with mating occurring over several days. Male monitors are endowed with two penis-like structures which allow them to mate on either side of the female. They may use them alternately or prefer one to the exclusion of the other. The sUlfaces of the hemipenes are amazingly convoluted and they vary so much 41

PllOM ;)41 JO Spll!Z'1

lOllUOW

Lifesty les of Monitors

Opposite: Courtship in water monitors (Indraneil Das)

Above: Bengal monitor excavating a termite mound (lndraneil Das)

43

Monitor Lizard s of the World between species that they are used as a taxonomic tool (Branch 1982; Bohme 1988). Females also have twinned appendages that are partly eversible and may represent glands which produce sexual pheromones·. Most records of counship and copulation in monitor lizards come from captivity, where animals have less opponunity to escape from each other and serious injuries are not W1common. Nevenheless mating is a dangerous activity and Auffenberg (1981) has suggested that pair bonding may occur between some male and female Komodo dragons. This does not imply any sort of monogamous relationship (as incorrectly stated by Seibert (1994)), but rather that acquainted animals mate with each other more than with other individuals and thus reduce the danger of sustaining injuries from an incompatible liaison. In bonded pairs mating is accompanied by much less preliminary courtship than in unacquainted animals and some counship behaviour may occur between the pair at times of year other than the mating season. The extent to which pair bonding exists in other monitor species is unknown, but reports of captive breeding indicate that it may be widespread. Female monitors have limited ability to store sperm and so eggs are always laid within a few weeks of mating. The eggs are covered with a flexible, leathery shell (Zwineberg (1972) fancifully portrayed monitors emerging from chicken eggs) which are very prone to desiccation in dry conditions. Therefore they must be deposited in a nest which provides the heat and humidity necessary for them to develop into fully-formed lizards. Monitor lizard nests are very carefully concealed and there are very few records of nests discovered in the wild (Tsselarius & Menshikov 1995 provide a detailed exception). In all species studied female monitors reach the peak of their activity as they begin to search for suitable nesting sites. They may have to fight against other females to gain access to good areas. Nests tend to be si tuated in an elevated position, presumably to reduce the danger of flooding. Despite many claims in the literature no monitor lizard eggs have been found in tree hollows. Many species deposit their eggs in chambers at the ends of burrows of varying depths which are always refilled to some extent. A number of test, or decoy holes may be dug nearby. Females may actively defend their nests for a few days after egg laying, but this behaviour does not persist for long before the weak and hungry lizard goes in search of food . For many species tennite mounds provide the perfect incubator. The female simply locates an active mound , tears a hole in it and deposits her eggs. For reasons not understood the termites do not destroy the eggs but quickly repair the damage done by the lizard, thus sealing the eggs inside. Active tennite mounds are maintained at almost constant temperatures and are much more humid than the surrounding air. Furthermore the nest is well protected from predators and as long as the mound is not abandoned by the termites the eggs are safe. Surprisingly many young monitors born in termite mounds do not feed on their guardians (Carter & King. pers.comm.). The construction of some tem1ite mounds allows the newly hatched lizards to escape via ventilation shafts that lead to the outside. but in other mounds they may be entombed. lacking the strength to break through the tough outer walls. The question of how these lizards escape from the mound has not been solved. Several times it has been suggested that the mother

• These structures are much more exciting (han I had anticipated -see Zeigler & Bohme ( 1995 ).

44 -j

Monitor Lizards of the World returns to the nest when incubation is completed and digs out the youngsters (Cogger 1967; Boonratana 19RH: Ehmann ct al 1991). Many people remain unconvinced that the monitor lizard is (;apaole of remembering her nesting site and returning there at the correct time and unfortunately the results of field work investigating this phenomenon are not available (Carter Il)H9: Boylan 1995). A television documentary which purported to show the release of hat(;hlings from a termite mound by their mother used broad artistic license (Marven I ':1':10). My own opinion is that a (;omplete lack of parental care in monitor lizards would be surpri sing, espet:ially in view of their apparently analogous evolution with snakes, many of whom protect their eggs throughout incubation. As well as utilising active termitaria many monitor lizards deposit eggs in mounds that are no longer inhabited by termites. An important distinction can be drawn between these behaviours. Although any monitor can lay its eggs in an abandoned mound the ability to use active mound may depend on special (probably chemical) adaptations that prevent the termites from recognising the eggs as foreign and destroying them. If this is the case it would suggest that the lizards are only able to make use of the mounds of certain species of termite. At present there is not enough data to confirm or refute this. Speed of incubation is determined largely by temperature and in the wild some eggs may take almost a year to hatch. Incubation times in captivity exist for most species but virtually none exist for eggs laid in the wild and the only published data on the conditions experienced in natural nests is provided by Ehmann et a/ 1991. Oearly it is beneficial if the young lizards emerge at a time of year when their is plenty of food available, but this is not always the case. The eggs of the desert monitor, for example. may hatch shortly before the onset of winter and the youngsters remain together in the nest until the following spring. In some species the development of the embryos may be completely halted during very cold weather and in others development may be completed months before the eggs hatch. Most hatch (and all emerge) from the nest at a time when insect abundance is high. They lead very secretive lives, remaining mainly in shady. humid microhabitats and feeding voraciously. Mortality is very high in the first year of life and the small amount of data available suggests that many eggs may fail to hatch at all (Ehmann et al 1991; Phillips & Packard 1994; Tsellarius & Cherlin 1':1':15) .

46

5

Monitor Lizards and Man

Our relationship with monitor lizards stretches back over 90,000,000 years. For almost all of this time they have been the predators and we the prey. The flTst documented cases of predation on monitor lizards by hwnans date back about 40,000 years (King 1962). Today mankind's relationship with the monitors is a complex one. They are undoubtedly the most important of the lizards to the human race

THE MONITOR IN FOLKLORE AND ART.

Monitors are often said to have provided the inspiration for mythological dragons, but many

other animals have equally strong claims. Marco Polo's description of the Great Serpents of

Karazan could eas.ily refer to a Komodo dragon:

"Here are great serpents ten paces in length and ten spans the girth of the body. At the forepart near the head they have two shon legs, each having three claws like those of a tiger, with eyes larger than a four-penny loaf and very glaring. The jaws are wide enough to swallow a man, the teeth are large and sharp and their whole appearance is so fonnidable that neither man nor any other animal can approach them without terror." The earliest known depictions of monitor lizards come from cave paintings near Bhopal made about I0,000 years ago (Das 1989). They frequently appear in ancient and modern Australian art, but they are conspicuously absent from the an of the ancient Egyptian civilisations. According to Rose (1962) monitor lizards were often depicted and embalmed by the ancient Egyptians. However the Egyptians did not begin to mummify reptiles until the later dynasties (about 4,000 years ago) when they were associated with the sun god Atum, and a search of the mummified reptiles in the British and Cairo Museums has not revealed a single sptx:imen of monitor lizard (Bennett & Monnor ms). The most likely reason that the varanids were excluded from the afterlife is that they prey on the eggs and young of crocodiles, which, although despised, were considered highly sacred by the ancient Egyptians. Folklore is rich in superstitions and anecdotes concerning monitor lizards. In some places they are despised or even feared, but many cultures appreciate the lizards and some hold them in great reverence. Stories that monitor lizards are venomous or even poisonous abound in the early literature. The siliva is considered poisonous in Bengal and in pans of Borneo they are always cooked with ginger as a precaution, because if a poisonous individual has been selected for the pot the mixture will tum black (Saha 1983; Auffenberg 1982). Mason & Theobald (in Gaddow 190 I) claimed that Burmese Karens ate monitor lizards, but discarded the heads btx:ause they considered them poisonous. The secretive rough-necked monitor was believed have so venom so strong it could kill an elephant (Lekagul 1969). In Sri Lanka water monitors are often considered unpalatable whilst Bengal monitors are eaten with relish (Deraniyagala I 0. (1)

00

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Lillie Book of Monitor Lizards in BenneiL 1'ilJ2d . Bayless & Huffaker 1\1\12, Rowell 1\1\14, Roder & Horn 1\1\14, Bayless 1')dllcli"n

AUFFENBERG .W . I'JK1c. Notes on feeding

hchaviour of Vumllu" hellxu/ell"i.\. J. Bombay N.H.S. of Varunus prasilllls kn,densis .11 the Dalla.< Zoo.

Proc. Replile Brecuing Symposium. Columhus:91·92 .

KII (2): 2K6·1112 .

AUFFENBERG.W. 19R(,. The Indian monilor 1i7Nd. BARNElT.B. 1979. Incuhation of Varalllls Rou/dii

eggs. Herpelofauna 11(1):21·22.

S:Ulcluary Asia. (, (4):127·111 .

AUFFENBERG.W. I'IKK. Gmy's Monilor Lizard .

BARNElT.B. 19R I. Ohservations on fish feeding

University of Florida. Gainesville.

repliles. Herpelofauna 11 (I): 11·11

AUFFENBERG.W. 1989. Exploilation of monitor

BARRElI.C.I928. Li7.ards in Australian wilds.

li/ClTUS in Pakislan. Unpuhlished consultancy report 10 Bull .New York ZooI.Soc. 11(4):

BARRElT.C. 1950. Repliles of Australia. CoL<SCI.

CITES .

Melbourne.

AUFFENBERG.W . 1989h. Utili7.aJion of monilor

li/~lTds in Pakistan. Tmffic Bull. 11(1):R·12.

BARmOLOMEW.G.A. & TUCKER.V .A. 1%4.

AUFFENBERG .W. 1994. The Bengal Monitor.

Size. body lemperalure.thermal conducuUlcc. oxygen

consumplion and hearlrale in Auslrali:Ul V:lTanid

UniversilY Of Florida Press.

AUFFENBERG.W. ARAIN.Q.N. & KURSHID,N . 1i7.11Tds. Physiol.ZooI. 37 (4): 341·154.

1'1'1 I. Mertcnsiella 2: 7 ·2R. Preferred habital. home BARTLElT.R.D. 19KI. NOles on caPlive

r.lII~e and movemenl pallerns of Varanus bengalensis reproduction of Varanus storri. Bull. Chicago Herp. Soc. 16 (3):65-66.

in SlIulhern Pakisl:Ul. AUFFENBERG.W. & AUFFENBERG.T. 1990. The BARTLElI.R.D. I 982.lnilial observations on Ihe

captive reproduction of Varanus storri. HerpelOfauna

replile lick AponomnuJ gervaisi as a parasile of 13(2):6-7

nlllllilOr lizards in Pakislan and India. Bull. Florida BATES,M.F. 1990. Varanus albigulariS. Rock

Mus. Nat. Hisi. BioI. Sci. 35(1)1-34. AUFFENBERG.W . & IPE.l.M . 1983. The food and Monilor. Hibernation . J.Herpel. Ass. Africa37:50

BAUER.P. 1972. Check 10 check . IntWldf. 2(1):54.

feeding of juvenile Bengal monitors (Varanus BAVERSTOCK.P.R .. KING,D., KING.M ..

h'·IIRO/,"si,,). J.Bomh.N.H.S. 80:119-124. BIRRELU .• KRIEG,M. 1993. The evolulion of the

AUFFENBERG.W .. REHMAN.H.• IFFAT of. & PERVEEN .Z. IlJR9. A sludy of Vuranusflavcscens. species oflhe Varanidae: microcmnplemenl fixalion

analysis of serum alhumens. Aus.J. Zoology

J.Bomhay. Nal.Hisl.Soc. 86 (3): 286-307. 41(6):621-638.

AUFFENBERG .W .. REHMAN.H .. IFFAT of. & PERVEENZ. 1990. Noles on the biology of Varanus BAYLESS,M.K. 1994. Zur Fortpllanzungshiologic

des Sleppenwaraans (Varunus examhc11Ultiru.r)

Kris"I1.1 k,,"ict'wvi. lBmnhay. NaI .HisI.Soc. 87 (I); 2h·1h. Salamandra 30 (2): 109-118.

BAHL.K.N . 1917. Rec. Indian Mus. 39: 133-174. BAYLESS,M.K. & HUFFAKER.R. 1992.

Skull of Vu,.unus monitor. Observalions of egg deposilion and hatching oflhe

BAHNOTAR.R.K. & SRIVASTAVA.Y.N. 1985. svannah monilor (Vurunus exanthematirus) in

hnpaci ofrepliles on food rroduclion and c.~ptivily. Varanews 3(1):5·6.

environment All India Sd. Wrilers. Soc. Res. PubL BAYLESS.M.K. & REYNOLDS.T. 1992. Breeding

nIl 2: 116·220.265-266 . of the savarmab monilor lizard in captivilY (Varanus

BAILON,S. 1992. Esc:unosos fosiles de facimiento de exanthematicus). SouthWest. Herp.Soc. 22(1): 12-14.

Mnreda (Plio,;en medin/superior. Gr.tnada. Espana. BECKER,H.O.. BOHME.W. PERRY,S .F. 1989. Die

Revisla. espanola de Palconlologia. Numero Lungen morphologic del' Warane und ihre syslCtnatis­ eXlraordimlTio 1992: 11-15. che slammersgeschichichlliche. Bonn. ZooL Beitr. 40

BALSAI.M. 1992. The general care and maintenance (1):27-56. of s;,vannah monilors and olher popular monilor BECKER.H.O. 1991. The lung morphology of sl'cdc.~ . Advanced Vivarium Systems, Lakeside. Varunus yemenensis BOHME el aI 1989, and il~ C'alii',>rnia. be:uing on the Syslemalics of Afro-Asian monitor BANERJEE.V. & BANERJEE.M. 1969. Seasonal Radialion. Mertensiella 2:29-37. BEEHLER,B.M. CRILL,W. JEFFERIES.B. & v'lTialion of erthrocyle number and haemoglobin con lent in a common Indian lizard Varanus mollitor lEFFEREIES,M. New Guinc.~ h;trpy eagle all em pIS 10 Ihcngalensisl. Z"ol .Anz. IR2: 203-207. caplure a monilOr lizard. Emu 92(4):24(,·247. BARBOUR .T. 1921. Aquatic skinks and aroore'f."r ' ~~-:~,~~, r(fi~.~~'i'..., J1l ,,,~ ;.t: ~., .... ~ ~.~i' "!wt!i:.,~~r:"':'i:! ..,.r ...;

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