White Cay iguana
Cyclura rileyi cristata
Description
The White Cay iguana is smaller than the San Salvador iguana (up to 280mm SVL), and can be distinguished by a combination of several scale features, including well-defined postsacral crest scales (Schwartz and Carey 1977). The dorsum of adults is usually gray with brown to orange-brown vermiculations. The dorsal crest scales, forelimbs, and portions of the head and face are typically highlighted in orange. Juveniles resemble young San Salvador iguanas, but lack a dark area in the pale zone of the middorsum.
Distribution
This subspecies occurs on only a single island, White (Sandy) Cay, in the southern Exumas of the Bahamas. This island is small, comprising about 25ha (Schwartz and Carey 1977). The iguanas were probably much more widely distributed during the last ice age when many of the Exuma Cays were presumably connected due to lower sea levels. They possibly occupied additional adjacent cays in recent centuries, but if so have vanished without a trace.
Status of population in the wild
The single population is confined to only one island, which can support only a limited number of iguanas. According to Lincoln-Peterson surveys conducted in 1997, the size of the population has been estimated at 150 to 200 individuals.
Ecology and natural history
Except for informal visits mainly to collect specimens, this isolated subspecies has been largely ignored by scientists. Essentially nothing has been published about its ecology or natural history.
Habitat
The vegetation of White Cay is fairly typical of the coastal rock habitat described by Smith (1993). The northwestern portion of the cay, where iguanas are least common, is comprised of a dense forest of thatch palm (Thrinax morrisii). The remainder of the cay is dominated by Strumpfia maritima and sea grape (Coccoloba uvifera) interspersed among rock and sand. Introduced Australian Pine (Casuarina litorea) is well-established along the low dunes of the southern shoreline. Seven-year apple (Casasia clusiifolia) dominates the sand dunes of several smaller cays to the south that are separated from White Cay by a narrow tidal flat that iguanas presently do not cross. In 1997, the vegetation appeared to be unaffected by Hurricane Lily, which scored a near-direct hit in October 1996. Iguana density is greatest along the periphery of the cay where rocky crevices are most numerous.
Threats
Illicit smuggling and the possibility of introduced animals are likely the greatest threats to this population. From photos that appeared in the April 1994 issue of a popular reptile magazine, it is clear that at least some C. rileyi, potentially from White Cay, have been recently smuggled. At least eight individuals of C. rileyi, presumably of this subspecies, were discreetly exhibited in the showrooms of several Florida reptile wholesalers in 1993 (R. Ehrig, personal communication), which suggests that more than a trivial number of animals were taken. Another potential threat is inbreeding depression, due to centuries or longer of effective isolation.
In 1996, S. Buckner, R. Carter, J. Iverson, and W. Hayes observed footprints of a raccoon on White Cay. It may have dispersed there on its own after several were formerly introduced to nearby Hog Cay. Although that animal has since been confirmed dead, it appears to have predated a significant proportion of the iguana population, particularly juveniles and females. Black rats formerly threatened the iguana population, but have since been removed from the cay.
Current conservation programs
A grant from the Chicago Zoological Society has facilitated eradication of black rats from White Cay. The project was a collaborative effort of the West Indian Iguana Specialist Group, the Bahamas National Trust, the Bahamas Department of Agriculture, Fauna and Flora International, Loma Linda University, and Zeneca Agrochemicals, Inc., which donated the rodenticide used in the eradication. Two cays that appear promising as potential sites for establishment of a second wild population of the White Cay iguana have been identified. Although they have yet to be surveyed on the ground, both look appropriate from the air, both are Crown land, and both have active seabird nesting colonies, a good sign that introduced predators are absent. W. Hayes and R. Carter visited White Cay in 1996 to obtain blood samples and other measurements from the iguanas and to evaluate their status.
Critical conservation initiatives
- Acquisition of White Cay within the park system of the Bahamas National Trust. The island is remote enough that local policing of the cay is unlikely.
- Institutional strengthening of responsible agencies to develop enforcement capabilities.
- Education programs discouraging visitors to the cay from dumping garbage and feeding iguanas.
Priority projects
- Maintain a program of rat control.
- Assess the current status of the population, and consider candidate cays for establishing a secondary population. It might be wise to consider a distant location (such as in the Land and Sea Park of the northern Exumas) as a safeguard against extinction resulting from weather.
- Conduct annual or biannual censuses of the population.
Contact persons
William Hayes
Department of Natural Sciences
Loma Linda University
Loma Linda, CA 92350 USA
Tel: (909) 824-4300 ext. 48911
Fax: (909) 824-4859
E-mail: whayes@ns.llu.edu
Ronald Carter
Department of Natural Sciences
Loma Linda University
Loma Linda, CA 92350 USA
Tel: (909) 824-4300 ext. 48905
Fax: (909) 824-4859
E-mail: rcarter@ns.llu.edu
David Blair
Cyclura Research Center
PMB #510, 970 West Valley Parkway
Escondido, CA 92025 USA
Tel: (760) 746-5422
Fax: (760) 746-1732
E-mail: critter@herpnut.com
Sandra Buckner
Bahamas National Trust
PO Box N4105
Nassau, The Bahamas
Tel: (242) 393-3821
Fax: (242) 393-3822
Email: sbuckner@bahamas.net.bs
