Exuma Island iguana
Cyclura cychlura figginsi

By Chuck Knapp

Description

The Exuma Island iguana is often regarded as the smallest of the three subspecies of C. cychlura. Although Schwartz and Carey (1977) list the animal as obtaining a maximum size of 315mm SVL, recent studies by C. Knapp indicate that individuals occasionally reach 470mm and 3.25kg (Bitter Guana Cay) to 542mm and 8.15kg (Leaf Cay). Barbour (1923) describes the Exuma Island iguana as being conspicuously different from the other subspecies in having tiny supranasals usually separated by a small, azygous scale and two pairs of prefrontals, the posterior pair of which is greatly enlarged.

Coloration is variable between populations. Adults from Bitter Guana and Gaulin Cays are dull gray-black with diffuse pale gray spots. The crest scales are either white or a light red. The head scales are black tinged with orange on the snout and infralabials (Schwartz and Carey 1977). Adults from Guana Cay are dull black with diffuse pale white ventral and gular coloration. The upper labial, temporal, parietal, nuchal and ocular scales are light blue, while the dorsal crest scales are either gray with red tinge or intense scarlet. Schwartz and Carey (1977) describe juveniles as possessing approximately seven black bands which become slightly diagonal laterally and alternate with pale gray bands. All bands are heavily mottled with small pale dots.

Distribution

The subspecies is known from seven small cays scattered over 80km throughout the central and southern Exuma island chain of the Bahamas. Anecdotal information suggests additional inhabited cays, but verification is necessary. The determination of range through historic records is problematic due to certain cays sharing multiple names (e.g., Guana = Prickly Pear = Noddy). Bitter Guana and Gaulin Cays constitute the northern extent of the population. Four cays, White Bay, Noddy, North Adderly, and Leaf Cays, all located northeast of Norman's Pond Cay, compose the nucleus of the range. Guana Cay, southwest of Great Exuma, forms the southern boundary of the population.

Status of populations in the wild

The exact size of the total population is not known. Formal surveys using standardized transect techniques have been conducted only on Guana, Gaulin, and White Bay Cays (Carey, 1976; Windrow, 1977; C. Knapp, unpublished data). The extent of the remaining population is based on estimations of iguana densities through comparative observations (J. Iverson, unpublished data; C. Knapp, unpublished data). Standardized and subjective survey techniques estimate the population to be between 1,000-1,200 animals.

While the majority of subpopulations appear relatively stable, some are in need of monitoring. Barbour (1923) refers to Bailey's collecting expedition on Bitter Guana Cay, from which the holotype specimen was procured, noting that "the iguana was found abundant on the Cay, no less than nineteen being taken in an hour or so." Three surveys of Bitter Guana in 1993, 1995, and 1997 yielded only seven total iguana sightings. Conversations with yachtsmen familiar with the area confirm that the iguanas are being taken as a food source.

Ecology and natural history

Except for the Guana Cay population, few formal natural history studies have been conducted. The Guana Cay population was studied in the 1970s (Wilcox et al. 1973; Carey 1976; Windrow 1977; Coenen 1995) and is currently being reinvestigated along with the other remaining populations (Knapp 1995; 1996).

Adult iguanas are herbivorous, and are arboreal as well as terrestrial feeders. Preferred food items are seasonally dependent and primarily consist of flowers, fruits, young buds, and leaves of Rachicallis americana, Reynosia septentrionalis, Strumpfia maritima, Jacquinia keyensis, Erithalis fruticosa, Coccoloba uvifera, Coccothrinax argentata, Eugenia axillaris, Suriana maritima, and the rotting fruit of Casasia clusiifolia (Windrow 1977; C. Knapp, unpublished data). Coenen (1955) reports the iguanas as coprophagous. They actively forage for the feces of the zenaida dove, Zenaida leucocephala, and the white-crowned pigeon, Columba leucocephala.

The iguana populations exhibit an unusual social system for the genus, displaying neither territorial nor hierarchical behavior. Carey (1976) suggests that this relaxed social structure allows the population to remain dense under conditions of limited resources. He further states that a hierarchical social system on small cays would retard genetic variation by restricting prime nesting sites, food supplies, and retreats to a few dominant animals. Adult iguanas have been seen basking in large aggregations without evidence of aggression towards conspecifics throughout the majority of their range (C. Knapp, unpublished data). At times, the iguanas demonstrate assertive and/or challenge displays in the form of headbobs. These usually only occur when one lizard violates the space of another or during sex recognition. When minor skirmishes do occur over preferred food items, the largest animal is always victorious (Windrow 1977; Coenen 1995).

Nesting has been observed on Guana Cay, with females digging a nest burrow approximately 61cm long and 8-13cm deep. Gravid females will actively defend an incomplete tunnel from conspecifics but will not defend the nest site after oviposition. The only excavations of nest chambers revealed three eggs each in two nests (Coenen 1995).

Habitat

The Exuma Island iguana utilizes a variety of habitats, including sandy beaches, xeric limestone devoid of vegetation, and areas of vegetation with or without sand or rock substrates. Limestone crevices and sand burrows are used as retreats at night and in adverse weather conditions. Presently, habitat appears to be relatively secure as cays supporting iguanas are small and free from human settlement. However, recent observations on White Bay Cay uncovered trails hacked through the interior and coconut palms planted on the beach. The island is currently for sale and in danger of tourist development.

Threats

Conversations with locals suggest that removal of animals from their home cays for tourist attractions elsewhere could constitute a significant threat. Although such activities probably occur on a small scale, they may reflect the larger problem of smuggling of iguanas from the Bahamas for illegal wildlife trade. Some cays are visited regularly by locals and yachtsmen, and dog tracks have been observed on Bitter Guana Cay. In addition to possible hunting pressure, predation by dogs may be contributing to the apparent decline of that population. In 1981, J. Iverson reported the presence of rats on Gualin Cay; this was subsequently confirmed by C. Knapp in 1995 (unpublished data). The effect of rats on this population is unknown, but past research indicates the detrimental consequences of rats on island reptiles (Cree et al. 1995). Certain cays possess diminutive nesting sites and the possibility of a season's recruitment being decimated by severe weather conditions is genuine.

The isolation of iguana-inhabited cays creates a problem for consistent population monitoring. Discrete environmental events including hurricanes could endanger certain populations. For example, Hurricane Lily engulfed Great Exuma and her satellite cays on 18 October 1996. The effects of Lily on the Guana Cay iguana population were not observed until May, 1997 (S. Buckner, personal communication).

Current conservation programs

All Bahamian rock iguanas are protected under the Wild Animals Protection Act of 1968. C. Knapp is continuing field surveys to assess current populations and to better define the geographic distribution of the subspecies. The Leaf Cay population was newly discovered in 1997. Blood samples are being collected from each study population to establish genetic profiles for different cays. Potential threats unique to each cay are being documented in order to provide the Bahamian government with information that will aid in setting conservation policies. Also, the vegetation and habitat condition on cays not currently supporting iguanas is being investigated for possible translocation programs.

The Bahamas National Trust has erected signs on Gualin Cay notifying the public of the protected status of the iguanas. The Bahamian government currently does not recognize any captive breeding programs, although unsanctioned breeding of these iguanas is apparently taking place in the United States.

Critical conservation initiatives

• Establishment of additional national parks to afford iguana populations more protection. Additional wardens and funds will need to be made available to patrol parks and monitor iguana populations.
• Implementation of an education program for locals and cruising yachtsmen to inform people of the rarity of Bahamian iguanas. Such programs should stress the detrimental impact that dogs, cats, and smuggling exert on small iguana populations.
• Continuation of efforts to instill in all Bahamian citizens national pride regarding their unique iguanas.

Priority projects

1. Determine the status of the population throughout its range.
2. Examine the possibility of translocations to other suitable cays.
3. Carry out genetic studies on all populations.
4. Conduct ecological, behavioral, and natural history studies on each population.
5. Establish a captive breeding program.

Note: The remoteness and inaccessibility of cays inhabited by iguanas makes field research expensive and time-consuming. The John G. Shedd Aquarium is currently funding research but other avenues for support need to be developed in order to accomplish the research goals in a timely manner.

Contact persons

Chuck Knapp
John G. Shedd Aquarium
1200 South Lake Shore Drive
Chicago, IL 60605 USA
Tel: (312) 939-2426
Fax: (312) 939-8069
E-mail: cknapp@ufl.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

Robert Ehrig
Finca Cyclura
29770 Mahogany Lane
Big Pine Key, FL 33043 USA
Tel: (305) 872-9811
Fax: (305) 745-8848
E-mail: ehriguana@aol.com