Excerpted from ©2004 by the Regents of the University of California. All rights reserved. May not be copied or reused without express written permission of the publisher. click here to BUY THIS BOOK 17 Conservation of an Endangered Bahamian Rock Iguana, I POPULATION ASSESSMENTS, HABITAT RESTORATION, AND BEHAVIORAL ECOLOGY William K. Hayes, Ronald L. Carter, Samuel Cyril, Jr., and Benjamin Thornton he bahamian endemic Cyclura rileyi Exumas. This taxon almost certainly occupied ad- Tis one of the most threatened of the West jacent islands (e.g., Leaf Cay, Hog Cay, possibly Indian rock iguanas. Two of its three recognized Little Exuma and Great Exuma) at one time, and subspecies, C. r. cristata and C. r. rileyi, are criti- has suffered substantial range contraction. C. r. cally endangered, and the third, C. r. nuchalis, is nuchalis exists naturally on just two cays (North endangered (Alberts, 2000). Although they for- Cay, 51.7 ha; Fish Cay, 73.9 ha) in the Acklins merly occupied large islands, today these lizards Bight, the immense, shallow body of water be- are confined to small, remote, uninhabited cays tween Crooked Island and Acklins Island. A third of three island groups in the Bahamas (the Exu- population, introduced to a small island (3.3 ha) mas, San Salvador Island, and the Crooked and within the Exumas Land and Sea Park, was es- Acklins Islands; figure 17.1). The island groups, tablished by five founders translocated from Fish each harboring its own subspecies, are on sep- Cay in the late 1970s by a private individual arate banks and therefore were not connected (S. Buckner, pers. comm.). This subspecies during the most recent ice age when water lev- was found on nearby Long Cay (23 km2) in the els were as much as 100 m lower than at pres- Acklins Bight in the early twentirth century ent. The cays are currently separated from adja- (Schwartz and Carey, 1977; Schwartz and Hen- cent larger islands by shallow water and were derson, 1991; Blair, 1992), and undoubtedly once probably formed within the past seven thousand occupied Crooked Island (238 km2) and Acklins years (when seas were more than 10 m lower Island (311 km2) as well. Thus, its current range than they are today; Kindler, 1995) from rising represents a tiny fraction (0.2%) of its former postglacial seas. range. The remaining populations of C. r. rileyi At present, C. r. cristata is restricted to a single are presently confined to six tiny offshore cays cay (White = Sandy Cay, 14.9 ha) in the southern and islets within the hypersaline lakes of San 232 FIGURE 17.1. Distribution of Cyclura in the Bahamas, including the three subspecies of Cyclura cychlura (on Andros, northern Exumas, and southern Exumas) and the three subspecies of C. rileyi (on southern Exumas, San Salvador Island, and Acklins Bight). C. carinata bartschi exists only on Booby Cay off Mayaguana Island, Bahamas; the second subspecies of C. carinata occurs in the Turks and Caicos Islands to the east. Salvador Island (31.5 ha total), although a few in- under the Convention on International Trade in dividuals are still encountered rarely on the main Endangered Species of Wild Fauna and Flora island (163 km2). Three additional populations (CITES), hunting and smuggling for the pet have been extirpated in recent decades from trade continue (Alberts, 2000). However, the Barn, High, and Gaulin Cays (30.3 ha total). As- greatest threats appear to be related to invasive suming the main island population is nonviable species that alter habitat and/or prey on iguanas. as a result of human habitation and environ- In this chapter, we describe the findings of a mental degradation, this taxon similarly occupies long-term, ongoing research program on C. ri- a mere fraction (0.2%) of its former range. leyi. At present, there are no legitimate collec- Although Amerindians apparently utilized tions of this iguana in captivity and all of our iguanas for food and funerary offerings (e.g., work has been in situ. We began our studies in Veloz Maggiolo, 1997; Winter et al., 1999) and 1993 with the short-term goals of identifying possibly transported them between islands, their all remaining populations of C. rileyi, obtaining impact on iguanas is otherwise unknown. Most accurate population estimates, evaluating the devastating was the large-scale destruction of general health of the iguanas and their habitats, habitat by European and American colonists, and assessing the threats to each population. who cleared forests from entire islands to estab- Our longer-term goals included more complete lish cultivation and introduced many non-native demographic analyses, measurement of mor- plants and animals. Today, in spite of protection phological and genetic variation, mitigation of CONSERVATION OF AN ENDANGERED ROCK IGUANA, I 233 TABLE 17.1 Summary of Annual Conservation Research Activities on the Three Subspecies of Cyclura rileyi year taxon activity 1993 C. r. rileyi Capture/marking (May) 1994 C. r. rileyi Capture/marking, population surveys (May, July) 1995 C. r. rileyi Capture/marking, population surveys (March, June, November) 1996 C. r. cristata Capture/marking (June) C. r. nuchalis Capture/marking (May–June) 1997 C. r. cristata Capture/marking, population surveys, behavioral ecology study (May–July) C. r. nuchalis Capture/marking, population surveys (May) 1998 C. r. cristata Rat eradication (April–May) C. r. nuchalis Capture/marking, population surveys, behavioral ecology study (May) C. r. rileyi Capture/marking, population surveys (June) 1999 C. r. cristata Population survey (October) C. r. nuchalis Capture/marking, population surveys, behavioral ecology study, post- hurricane assessment (May–July, October) C. r. rileyi Capture/marking, population surveys, behavioral ecology study, rat eradication, post-hurricane assessment (June–July, October) 2000 C. r. cristata Population survey (November) C. r. rileyi Population surveys, rat eradication (May, June–July) 2001 C. r. rileyi Population surveys, nest habitat restoration, behavioral ecology study (June–July, October) Notes: Whereas the majority of expeditions were brief (one to two weeks) and sometimes several times per year, the behav- ioral ecology studies encompassed five ten-week field seasons. threats to the habitats of several important cays, of our findings appear in three student theses and detailed studies of behavioral ecology. A (Thornton, 2000; Cyril, 2001; Fry, 2001) and in summary of our annual research activities is an earlier paper (Hayes et al., 1995), most of provided in table 17.1. our data remain to be published. Here, we sum- We begin by providing detailed assessments marize our major findings from years of field of all known C. rileyi populations, including research and focus on how the findings benefit demographic measures, habitat characteristics, our understanding of iguanas in general and and identified threats. Next, we describe and as- their conservation. sess several projects undertaken to control non- native predators and restore damaged habitats. POPULATION ASSESSMENTS Subsequently, we provide highlights from our detailed studies of the behavioral ecology of We visited each of the known populations of several populations. In the following chapter C. rileyi to systematically survey population size, (Carter and Hayes, this volume), we present measure morphological features, and assess analyses of morphological and genetic variation other demographic attributes (e.g., sex ratio, within and between the three taxa, and discuss body-size distribution). We also informally sur- conservation recommendations. Although some veyed the habitats of each cay and identified po- 234 WILLIAM K. HAYES ET AL. tential threats to iguanas. The ownership and subadults (12–19.9 cm), adults (20–27.9 cm), geophysical and ecological features of each cay and large adults (>28 cm). Most iguanas were are summarized in table 17.2. The demographic probed for sex identification. characteristics of and primary threats to each population are provided in tables 17.3 and MARKING INDIVIDUALS 17.4. On the larger islands, there are additional Prior to release at the site of capture, iguanas problems related to human-commensal animals were marked semipermanently by affixing one (pets and livestock) and substantial habitat al- to three colored glass beads on each side of the teration. Although the killing of iguanas for food nuchal crest with an 80-lb nylon monofilament persists in other regions of the Bahamas and line melted into a ball at each end to retain the Carribean (e.g., Alberts, 2000; Knapp, 2001b), beads (Rodda et al., 1988; Hayes et al., 2000). we have found no evidence of current hunting When conducting home range and behavioral of C. rileyi. ecology studies, we additionally marked all indi- viduals with a temporary alphanumeric code on SAMPLING METHODS each side of the dorsum, visible from a distance, DATA TREATMENT AND ANALYSES using a nontoxic enamel paint that lasted several Statistical tests were conducted using SPSS months or until ecdysis (Hayes et al., 2000). for Windows (release 8.0, 1997; SPSS Inc., Our observations and those of others suggest Chicago, Illinois), with α=0.05. Both paramet- that neither beads nor paint marks interfere with ric and nonparametric tests were conducted, de- normal behavior or survival (but see Hayes et al., pending on the data properties. For some data, 2000; Murray and Fuller, 2000). transformations (e.g., log or rank) were required prior to analyses. In some cases, we report para- POPULATION SURVEYS metric tests of data that failed to meet paramet- We estimated population sizes by three means, ric assumptions, but when possible, we used as summarized by Hayes and Carter (2000): nonparametric alternatives to confirm suitabil- (1) Lincoln-Petersen mark-resighting surveys ity of the parametric tests. For multivariate tests, on small cays (<12 ha) having sufficient marked effect size (proportion of variance explained by iguanas; (2) classical transects (standard counts an independent variable) is indicated in some of all iguanas seen) that covered the entirety of cases by η2.