1 International Aruba Island Rattlesnake Studbook CROTALUS UNICOLOR Compiled by: Stan Mays Curator of Herpetology Houston Zoo, Inc. 1513 N MacGregor Houston, TX77030, USA Telephone: (713)533-6510 Fax: (713)533-6755 Email [email protected] (713) 533-6527 Data current as of 22 December 2007 2 TABLE OF CONTENTS Preface 3 Studbook Disclaimer 3 Current Status of the Captive Population 3 Introduction and Natural History 4 Conservation Status 4 Captive Management 5 Husbandry and Reproduction 5 Incoming/Outgoing Specimens 5 Housing 5 Temperature 6 Photoperiod and Lighting 6 Feeding/Nutritional Requirements 6 Reproduction 6 Description of Data Fields 7 Bibliography 8 Living and Historical Specimens Listed by Studbook Number 10 Living and Historical Specimens Listed by Institution 57 Institution Glossary 199 3 PREFACE This is the second edition of the Aruba Island Rattlesnake International Studbook and replaces the one published in 1999. Over the past several years many people too numerous to mention have offered constructive advice during the preparation of this studbook. Thank you to all of them, and to the support the Houston Zoo has given. Thanks also to the many registrars, curators, animal keepers, and others who took the time and effort to answer my requests for information and did so in a timely manner. Hopefully, the material in this studbook will be useful to them. Finally, thanks to Andy Odum for all the conservation work he has accomplished on Aruba and who has made the Aruba Island Rattlesnake SSP a model program. STUDBOOK DISCLAIMER Copyright 2008 by the Houston Zoo, Inc. All rights reserved. No part of this publication may be reproduced in hard copy, machine-readable or other forms without advance written permission from the Houston Zoo, Inc. Members of the American Zoo and Aquarium Association (AZA) may copy this information for their own use as needed. The information contained in this studbook has been obtained from numerous sources believed to be reliable. AZA and the Houston Zoo, Inc. make a diligent effort to provide a complete and accurate representation of the data in its reports, publications, and services. However, AZA and the Houston Zoo, Inc. do not guarantee the accuracy, adequacy, or completeness of any information. AZA and the Houston Zoo, Inc. make no warranties or representations of any kind, express or implied, including but not limited to warranties of merchantability of fitness for particular purpose. AZA and the Houston Zoo, Inc. disclaim all liability for errors or omissions that may exist and shall not be liable for any incidental, consequential, or other damages (whether resulting from negligence or otherwise) including, without limitation, exemplary damages or lost profits arising out of or in connection with the use of this publication. Because the technical information provided in the studbook can easily be misread or misinterpreted unless properly analyzed, AZA and the Houston Zoo, Inc. strongly recommend that users of this information consult with the studbook keeper in all matters related to data analysis and interpretation. CURRENT STATUS OF THE CAPTIVE POPULATION Number of living individuals in population as of 22 December 2007: International: 66.72.37 (175) in 50 institutions. North America only: 56.63.4 (123) in 45 institutions. Historic number of individuals in population as of 22 December 2007: International: 208.225.103 (536) in 69 institutions. North America only: 193.212.37 (442) in 56 institutions. 4 INTRODUCTION AND NATURAL HISTORY The Aruba Island Rattlesnake (Crotalus durissus unicolor), despite its presence on the fairly densely populated island of Aruba in the Caribbean, is one of the lesser known members of the Crotalids in regards to its life history and ecology. Since it was first described (van Lidth de Jeude, 1887), relatively little information concerning its habits have been documented even though there have been several field studies done on the species recently(Odum and Goode, 1989; Goode et. al., 1990; Reinert et. al., 1992; Reinert et. al., 2002). The Aruba Island Rattlesnake is endemic to Aruba Island, which is a small arid island (175 km²) located 24 km north of the coast of Venezuela. Annual rainfall averages 22 centimeters, although this can vary (Peterson, 1992). The average temperature is 37 Celcius, which remains fairly constant due to Aruba’s proximity to the equator, as does the annual photoperiodic cycle. There is a definite wet/dry season, with most of the rain falling from September through January (Peterson, 1992). Like the Galapagos, Aruba is an oceanic island and has never been connected to South America. Despite its small size, Aruba is inhabited by ~75,000 people, which gives it a fairly dense population. Most people, however, live along or close to the coastline, while the rattlesnake is now restricted to the mostly undeveloped interior part of the island. It historically is thought to have ranged over the entire island (Odum, 1992), although it is possible that C. d. unicolor has always been restricted to the general locale that it currently inhabits. A long term field study by Reinert et. al. (2002) showed that no rattlesnakes were ever observed in a 14 year period on the low elevation, sandy soil habitats of the western part of Aruba. Crotalus durissus unicolor is a small to moderate size snake (<1.0 meter). It is pale tannish in color with a series of diamond-shaped blotches along its dorsum, which often are hard to distinguish in adults to the point where they may appear to be totally uniform in color. There has been some discussion as to whether or not C.d.unicolor should be accorded full species status, or if it is a dwarf subspecies of Crotalus durissus (for a review, see Strimple, 1987; Campbell and Lamar, 1989). According to Campbell and Lamar (1989, 2004), however, C.d. unicolor appears to be comparatively recently derived from a mainland form of C. durissus. Furthermore, a study of microsatellite genetic markers indicated a close relationship between the rattlesnake populations on Aruba and in South America (Bushar et. al., 2001). C. d. unicolor, then, does appear to be a dwarf subspecies of C. durissus. For the purposes of this studbook, we will identify the Aruba Island Rattlesnake as Crotalus durissus unicolor. C. d. unicolor is usually found only within a 45 square kilometer area in the undeveloped interior (cunucu) of Aruba, although its range is a 76 km² area of the eastern part of Aruba representing approximately 43% of the island (Reinert et. al., 2002). This section of Aruba is characterized by hills tranversed by deep ravines (Odum, 1992)and is largely uninhabited. It has been found from sea level to 189 meters (Reinert et. al., 1992). Habitat in the cunucu includes thorny deciduous and evergreen woodland, small brushy thickets, and cactus. Aruba Island is thought to have been more densely forested in the past (Reinert et. al., 1992), but most trees have long since been cut down for a variety of uses. Uncontrolled grazing by sheep, goats, and donkeys also affect unicolor habitat. The Aruba Island Rattlesnake is the top native terrestrial predator on Aruba Island, although feral dogs and cats are now present (Chizar, 1992). However, the exact composition of the diet in wild C. d. unicolor has not yet been fully ascertained, although Klauber (1972) reported that rabbits and lizards were preferred dietary items. However, newly captured snakes appear to have a distinct preference for rodents, although lizards are also accepted (Odum and Goode, 1989). Since there are high densities of whiptail lizards on Aruba, it is reasonable to assume that juvenile and adult rattlesnakes occasionally include them in their diet (Peterson, 1992). In terms of reproduction, wild C. d. unicolor breed in January to early February (at the end of the wet season) and young are born in early June or July, with an average of 10 young born (Goode, 1992). Although this species has bred as early as two or three years in captivity, wild specimens probably do not breed until 4-6 years of age (Odum, 1992). No data has been collected on the natural maximum life span, but ages of 20 years are not uncommon in captivity. CONSERVATION STATUS The population of wild C. d. unicolor has been optimistically estimated to be no more than 500 adult animals; field studies suggest that the total population may be less than 225 adults. A long term radiotelemetry study resulted in a total of 187 specimens being captured and PIT tagged over an eleven year period (Reinert et. al., 2004). However, wild populations in snakes generally 5 are difficult to estimate (Fitch, 1987). Historical accounts suggest more abundance and a wider distribution than at present (Odum, 1992). The PHVA analysis conducted in 1992 warns that a reduction of habitat to below 40 square kilometers will put unicolor’s wild population in serious jeopardy. In any case, the wild Aruba Island rattlesnake population appears to be in a steady decline, due to its limited habitat and range, and should be considered rare (Odum, 1992). Major reasons for the rattlesnake’s decline appear to be loss of habitat and negative incidental contact with humans (Odum, 1995). Another concern affecting the Aruba Island rattlesnake is the fairly recent introduction of Boa constrictor on Aruba. This species has now established itself on Aruba and may be an important competitor with unicolor for scarce prey resources. A field research project to examine the potential impact of the Boa on the rattlesnake and other native Aruba species is an important component of the latest SSP Masterplan (Odum, 2007). Over the past several decades, C. d. unicolor has been given increased protection from several different sources. It has been listed as a Threatened Species by the United States Fish and Wildlife Service since 1983, and is also listed as threatened by the IUCN.