BEHAVIOR AND ECOLOGY OF THE ROCK IGUANA CYCLURA CARINATA By JOHN BURTON IVERSON I I 1 A DISSERTATION PRESENTED TO THE GRADUATE COUNCIL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 1977 Dedicat ion To the peoples of the Turks and Caicos Islands, for thefr assistances in making this study possible, with the hope that they might better see the uniqueness of their iguana and deem it worthy of protection. ACKNOWLEDGMENTS express my sincere gratitude to V/alter Auffenberg, I vjish to chairman of my doctoral committee, for his constant aid and encourage- ment during this study. Thanks also are due to the other members of my committee: John Kaufmann, Frank Nordlie, Carter Gilbert, and Wi 1 lard Payne. 1 am particularly grateful to the New York Zoological Society for providing funds for the field work. Without its support the study v;ould have been infeasible. Acknowledgment is also given to the University of Florida and the Florida State Museum for support and space for the duration of my studies. Of the many people in the Caicos Islands who made this study possible, special recognition is due C. W. (Liam) Maguire and Bill and Ginny Cowles of the Meridian Club, Pine Cay, for their generosity in providing housing, innumerable meals, access to invaluable maps, and many other courtesies during the study period. Special thanks are also due Francoise de Rouvray for breaking my monotonous bean, raisin, peanut butter, and cracker diet with incompar- able French cuisine, and to Gaston Decker for extending every kindness to me v;hile cj Pine Cay. They enriched my visits to the islands more thd.'. any other tv/o persons. For similar courtesies I also thank George and Marou Nipanich. I am also indebted to many other Turks and Caicos islanders for information and help throughout my study. Don Correl], Bob Anderson, and Walter Auffenberg supplemented my plant collections and identified most of the plants. Don Buden supplied a list of birds recorded from the Turks and Caicos Islands. Arthropod identifications were made by Bob V/oodruff (insects), and Martin Huma (solpugids and scorpions). Walter Auffenberg and David Auth unselfishly allowed me access to their Caicos Islands field notes. Diderot Gicca and Tom Wiewandt generously shared with me their field experiences with other species of Cy£l_ura_. Aerial photography of the study islands was made possible by Bill and Ginny Cowles. Numerous others have, in one way or another, added to the successful completion of this vjork; I apologize for my failure to acknowledge each one individually. My wife. Sheila, typed the numerous manuscript drafts, endured my frequent absences from home, and supported me in many ways during all phases of the work. All illustrations are the work of the author. TABLE OF CONTENTS Page ACKNOWLEDGEMENTS I I I ABSTRACT vii INTRODUCTION 1 Purpose ) Systematic Relationships and Distribution 2 Study Area 3 Zoogeographic Relationships 9 Materials and Methods 10 MORPHOLOGY 25 HABITAT 35 CI imate 35 Soil he Vegetation hS Burrows , 58 REPRODUCTION 68 Male Sexual Cycle 68 Fetnale Sexual Cycle 70 Courtship and Mating 76 Nesting 9I Egqs, Incubation and Hatching 103 Fertility, Prenatal and Natal Mortality II3 Genera! Seasonal Reproductive Pattern II5 Reproductive Effort and Strategy 1)8 GROWS H 136 General Pattern I36 Factors Affecting Growtn I7I Longevity 172 Regeneration 172 Coinparisoni; With Other Iguanineb 173 FOOD AND FEEDING I80 oi^^t 190 Feeding Behavior 1 gO Gastrointestinal Tract Anatofny 202 Digestive Efficiency 211 Fat Bodies 213 Food as a Limiting Factor 217 h'erbivory as a Feeding Strategy 220 ACTIViTY AND MOVEMENTS 22't Locor:otion 22'> Retreats 225 Activity Cycles 225 SOCIAL ORGANIZATION 255 Displays 255 Dominance Relationships 2/2 INTERSPECIFIC COACTIONS 286 Natural Cohabitants 286 Introduced Cohabitants 287 Broken Tail Frequency 292 Epifauna 298 Endofauna 299 DENSITY AND DEMOGRAPHY 305 Sex Ratio 305 Characteristics of Juvenile Population 305 Characteristics of Adult Populations 3]if Life Tables 328 Life History Strategy 332 OUTLCOK 337 Populations on Turks and Caicos islands 337 Basic Lizard Requirements 347 Population Control ^^3 Conclusions. 352 LITERATURE CITED 353 EICGRAPHICAL SKETCH 379 Abstract of Dissertation Presented to the Graduate Council of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy BEHAVIOR AND ECOLOGY OF THE ROCK IGUANA CYCLURA CARINATA By John Burton Iverson III June, 1977 Chairman: Walter Auffenberg Major Department: Zoology The natural history and social behavior of the rock iguana, Cyclura carinata, was studied during 25 weeks between September, 1973, and June, 1976, on several small cays in the Turks and Caicos Islands, British West Indies, and in captive enclosures in Gainesville, Florida. Reproductive cycles were synchronized to climatic cycles. Testes sizes were maximal in April and May (the end of the dry season). Vi tel logenesis began in January (beginning of the dry season); ovulation and mating occurred in early May. Courtship was typical of most iguanid lizards; the mating system v/as probably primarily monogamous with serial polygyny among some males. A single annual clutch of two to nine eggs was laid in early June in the terminal portion of the female's retreat burrow. Clutcn size was positively correlated with female size. Clutch v^/eight averaged about 25^^ oF preoviposi t ion weight. Females defended their nest burrows for several days to several weeks after nesting, but were not territorial during the remainder of the year. Hitching occurred after approximately 90 deys. Neonates averaged 79-8 mm SV and 1^.6 gm. Juvenile growth rate averaged 132 mm SV/year. Males reached s-^xual maturity at approximately 220 mm SV and 375~^75 gm, at an age of about seven years; females, 185-200 mm, 200-300 gm, and six to seven years. Adult males averaged 276 mm SV and 935 gm; adult females, 225 mm and ^75 gm. The largest male measured 360 mm SV and 1864 gm; largest female, 292 mm and 1135 gm. Adults grew between 2 and 17 mm SV/year. Rock iguanas were primarily herbivorous at all ages, and fed arboreally and terrestrially. Five partial septa partition the proximal colon region; this modification presumably increases digestive efficiency. Huge oxyurid nematode populations inhabited the colon, and their relation- ship with the iguana may be mutual istic rather than parasitic. Abdominal fat deposits were negatively correlated with gonadal activity. Home range was correlated with body size and habitat productivity, 2 2 and averaged 98O m for females, 1260 m for subdominant males, and 1590 2 m for dominant males. Diurnal activity was bimodal during warmer months; high midday temperatures resulted in reduced activity. Winter activity v/as generally reduced and peaked at midday. Iguanas basked following emergence; most of the remainder of the day was spent feed- ing, interacting with other lizards, and shuttling in the sun-shade mosaic for Lharmoregulatory purposes. Basking preceded the termi- nrition uf dsily activity Roi.k iguanas performed ritualized "signature" displays or head- bobs. Postural adjustments v^ere among the modifiers producing variation in this display in different behavioral contexts. Displays were important to territory declaration,, male chal lenging, and sex recognition. Males were territorial year-round in the field, but developed dominance hierarchies in captivity. Dominant males displayed less than subor- diniites. Male territorial defense probably evolved as a mechanism guaranteeing access to 1) food resources, and 2) females for breed- ing. Sex ratio was 1:1 in all age classes. Survivorship was positively correlated with body size. Juvenile densities reached 90.3/ha in optimum habitat, adults exceeded 31.1/ha. Biomass estimates were 5.15 kg/ha for juveniles and 17-01 kg/ha for adults. Life table data indicate replacement rate was near unity, and mean generation time was U.O years. In its life history strategy, C_. carinata is a predominately K-selected species. Cyclura are vulnerable to few native predators, but suffer drastic population reductions with the introduction of feral mammals. Virtually the entire iguana population of one study island (> 15,000 individuals) was extirpated by dogs and cats during the course of this study. The status of Cyclura carinata in the Turks and Caicos Islands was assessed and a management program congruent with the most critical aspects of the life history of the rock iguana was recommended. INTRODUCTION Purpose The genus Cyclura is one of tha most poorly known lizard genera in North America, despite being one of the most conspicuous members of the West Indian fauna. Although a sizeable literature exists regarding the genus, most of the references are faunal lists or general works and contain only anecdotal information; no thorough autecological study of any of the species has been made. Few New World lizards have experienced as intimate a relationship with man, and suffered more from the interaction, than Cycl ura . Major populations have been extirpated within historic times. Probably no presently existing population is entirely free from pressures induced by man and his animals. It is increasingly clear that a thorough knowledge of the habits and adaptations of our fauna Is necessary if we are to be able to insure their survival in the face of continuing and increasing cohabitation with humans. It V'jas for these reasons that study was begun on a still relatively common species: Cyclura carinata , the Turks Island iguana. From September, 1973, through June, 1976, C_. carinata was studied both in the field in the Turks and Caicos Islands and in the laboratory. The goals of the study viere: l) to obtain data on the behavior, adaptations, life history, and community role of this species; 2) to detert^Ine i/hat factors limit population size; 3) to propose methods by which the species might survive cohabitation with man, v;i thout threat 1 i of extinction; and h) to provide an indepth charter study for extrap- olation to sirTiilar investigations of other less common and more endangered species of Cyc lura in the 'West Indies.