Department of Earth and Biological Sciences
Faculty: William K. Hayes
Laboratory of behavioral ecology and conservation
Shawn K. Fry (MS, 2001)"Ecology of the endangered Sandy Cay rock iguana, Cyclura rileyi cristata, in the Bahamas." (PDF - 1.32 MB)
Contact - Shawn has graduated.
Shawn Fry extracts blood from an endangered iguana. Photograph: William K. Hayes.
Shawn spent much of the summer of 1997 on a tiny island at the southern end of the Exumas Islands in the Bahamas. While there, he undertook studies of population size, mortality, and home range size of the only population of Cyclura rileyi cristata in the world. After we learned in 1996 that Sandy (or White) Cay was rat-infested and also harbored a feral raccoon, Sean's initial objective was to evaluate raccoon and rat predation on iguana nests. Unfortunately, when we returned in 1997, there were so few iguanas, and females in particular, that he was unable to capture a single reproductive-sized iguana, much less locate any nests. Sean managed to terminate the raccoon, and the rats were eradicated a year later. You can read more details of his study in the thesis abstract below or in my account of Research on Endangered Bahamian Rock Iguanas. The postscript to this story, however, is that as of fall 2002, we have seen a steady recovery of this iguana on Sandy Cay. Regrettably, we have not found the means to implement a translocation or headstarting project.
Thesis abstract
In this thesis, I present the results of a study on the population demographics and home range size of Cyclura rileyi cristata. There are eight species of West Indian rock iguanas, genus Cyclura. All are endangered, including C. rileyi, which is endemic to the Bahamas. One of three recognized subspecies, C. r. cristata lives on a single cay in the Exumas chain and is among the most endangered lizards in the world. Various size measurements indicate that this taxon is among the smallest within the genus. Distance surveys and a Lincoln-Petersen estimate based on resightings of marked iguanas suggest that the total population is comprised of 134-204 animals. In contrast to other populations of C. rileyi sampled by similar means, the sex ratio was highly skewed toward male iguanas (95% of noose captures). Thus, as few as 10 female iguanas may remain in the population. Glue-traps set near burrows proved to be more effective than noosing for the selective capture of females. However, no females of reproductive size were captured. Three non-native mammals were found on Sandy Cay, including rats (Rattus rattus), mice (probably Mus musculus) and a single raccoon (Procyon lotor). Several estimates based on capture rates and resighting ratios suggested that the raccoon inflicted considerable mortality on adult iguanas (35-67% between 1996 and 1997). Comparisons of density among rat-infested versus rat-free populations and attacks observed on lizard models suggest that rats negatively impact C. rileyi populations. Home range estimates based on radio-tracking of iguanas showed highly variable home range sizes that, in males, may exceed those of other C. rileyi populations. Remarkably few social interactions were observed, which was probably a consequence of low population density. Based on these findings, I offer several recommendations for the conservation of this critically endangered lizard, including translocation and captive headstarting programs to begin a new population and formal protection of the island as a National Park.
Fry, S. K. 2001. Ecology of the endangered Sandy Cay rock iguana, Cyclura rileyi cristata, in the Bahamas. Unpublished MS thesis, Loma Linda University, Loma Linda, California.