Overview of West Indian Iguana Populations

As a group, West Indian iguanas are among the most endangered lizards in the world, probably due in large part to their exclusively insular distribution. As a result of their low metabolic rates and naturally high population densities, lizards in many mainland habitats are relatively resistant to extinction. However, the restricted ranges and small population sizes of lizards on islands render them highly susceptible to a variety of human-caused threats. Pressure to exploit undisturbed natural areas is particularly strong in the West Indies, where unutilized land is often perceived as economically undesirable (Barzetti 1993). Recolonization following local extinction on islands may be quite rare because West Indian iguanas, like most other terrestrial reptiles, are probably poor over-water dispersers.

According to IUCN Red List Categories (IUCN 1994), four West Indian iguanids are considered Vulnerable, five Endangered, and eight Critically Endangered. Two taxa, the Turks and Caicos iguana (C. carinata carinata) and the Cuban iguana (C. nubila nubila), are still fairly numerous in the wild. However, both have been nearly extirpated on the larger, more populous islands within their ranges, and today are restricted primarily to smaller, uninhabited islets or cays. Although both still exist over a wide area, they are subject to a variety of human disturbances, with the Turks and Caicos iguana reduced to 10% of its former range. The rhinoceros iguana (C. cornuta cornuta) and the Andros Island iguana (C. cychlura cychlura), both ranked as Vulnerable, inhabit increasingly fragmented ranges and are threatened by invasive exotic species. Although it still occurs on many islands, the Lesser Antillean iguana (I. delicatissima) is undergoing very rapid decline as a result of habitat loss, competition with introduced goats, predation by exotics, and hybridization with common iguanas (I. iguana).

Of the West Indian iguanas ranked as Endangered, the majority occur in the Bahamas (the Exuma Island iguana, C. cychlura figginsi; the Allen's Cay iguana, C. cychlura inornata; the San Salvador iguana, C. rileyi rileyi; and the Acklins iguana, C. rileyi nuchalis). All of these taxa are restricted to a limited number of small islands or cays, often no more than a few hectares in area. While populations are generally stable, many of these islands are heavily visited by tourists and some taxa have been subject to illegal smuggling in recent years. The Mona Island iguana (C. cornuta stejnegeri) occurs only on the remote island of Mona, where it is scarce due to predation by feral pigs and cats, browsing by feral goats, and destruction of nest sites.

While very small, the single population of Bartsch's iguana (C. carinata bartschi) in the Bahamas appears to be healthy and stable, supporting all age classes. However, this subspecies is restricted to one tiny cay with a high point of 6.2m and most of its area below 3m. Because environmental catastrophe, particularly in the form of a heavy hurricane, is a very real threat, this species has been ranked as Critically Endangered. Another Bahamian form, the White Cay iguana (C. rileyi cristata), has only one small population remaining from which illegal smuggling has been confirmed. The Jamaican iguana (C. collei), the Lesser Caymans iguana (C. nubila caymanensis), the Grand Cayman iguana (C. nubila lewisi), the Anegada Island iguana (C. pinguis), and Ricord's iguana (C. ricordi), are probably currently far below natural carrying capacity on the islands where they occur.

Active iguana nesting site in the Hellshire Hills, Jamaica.

The Jamaican iguana was believed extinct until the 1990 rediscovery of a tiny remnant population in the remote Hellshire Hills. Since that time, a highly successful captive rearing program involving over 100 juveniles has helped provide a hedge against extinction, but the wild population is still very much in peril. For the Lesser Caymans iguana, the only remaining viable subpopulation is that on Little Cayman, and it is subject to a variety of threats, particularly habitat loss and introduced predators. Based on recent genetic data, the Grand Cayman iguana has probably existed at an extremely small population size for an even longer period than the Jamaican iguana. Genetic variation among the remaining individuals examined thus far appears to be very low, posing serious concerns regarding conservation efforts for this taxon. The Anegada Island iguana has undergone precipitous declines in recent years, primarily due to competition with feral livestock for food and predation by feral cats. The population of Ricord's iguana, historically small and disjunct, is declining as a result of habitat degradation and introduced species.

Table 2. Current Status of West Indian iguana populations according to the 1996 IUCN Red List. See Appendix 2 for explanation of listing criteria.

† Although the population estimate for this taxon is relatively large, its range has contracted significantly in recent years.

Remains of a charcoal kiln in the Hellshire Hills, Jamaica.