The Jamaican iguana is a moderate-sized rock iguana, with SVL reaching 428mm in males and 378mm in females. Schwartz and Henderson (1991) describe coloration as green, grading into slaty blue with oblique lines of dark olive-green on the shoulder. Three broad triangular patches extend from dorsal crest scales to venter, with dark olive-brown zigzag spots. The dorsal crest scales are somewhat brighter bluish-green than the body. The top of the head is washed green and the dorsal and lateral body surfaces are blotched with straw, with the blotches breaking up into small groups of spots. Wild individuals, particularly nesting females, often appear deep reddish-brown in color after digging in the coarse ferralic soils of the Hellshire Hills region.
According to Sloane (1725) who visited the island in 1688, iguanas were once common in Jamaica although their distribution seems to have been restricted to the drier sections of the south coast, at least in historic times. The Jamaican iguana declined dramatically during the second half of the 19th century, probably due to the introduction of the Indian mongoose (Herpestes javanicus [=auropunctatus]), changing land use patterns, and human population growth. Today, the iguana survives only in the Hellshire Hills, a rugged limestone area of 114km2 with fringing wetlands and beaches located 20km west of Kingston. Despite their closeness to Jamaica's densely populated capital, the Hellshire Hills persist as a wilderness area because of their ruggedness and lack of surface water, making them unsuitable for agriculture and large-scale settlement.
Status of population in the wild
At the beginning of the century, the Jamaican iguana was thought to have survived only on the Goat Islands, two small islets off the Hellshire Hills. The species was believed extinct after this population disappeared in the 1940s. However, the continued survival of the Jamaican iguana in the Hellshire Hills was confirmed in 1970, and again in 1990. A preliminary survey in 1990 revealed a small surviving population of perhaps a hundred or so animals in the least disturbed central and western sections of the Hellshire Hills, and two active nesting sites. Iguanas have disappeared from northern and eastern sections of the Hellshire Hills because of extensive charcoal production, use of dogs for pig hunting, and human settlements. There may be no more than a hundred adults remaining in the wild, and juvenile recruitment appears to be minimal.
Ecology and natural history
Rugged limestone outcroppings make up much of the Hellshire Hills, although coarse red ferralic soil has accumulated in crevices and depressions. Soil suitable for nesting is comparatively rare. The vegetation of the Hellshire Hills consists of varying formations of tropical dry forest. The area supports about 300 species of higher plants, including 53 endemics. Jamaican iguanas are found only in the remotest sections of the Hellshire Hills where the forest remains in good condition. Jamaican iguanas feed on leaves, fruits, and flowers of a wide variety of plant species, supplemented occasionally by animal matter, including snails. Diet composition changes seasonally according to the flowering and fruiting cycles of local plant species.
Following the rediscovery of the Jamaican iguana in 1990, the two known communal nest sites have been observed intensively (Vogel 1994). Nesting occurs in underground tunnel systems of nest burrows filled with loose soil. Gravid female iguanas begin digging trial holes long before egg laying. Females deposit their eggs in mid-June, and hatchlings emerge approximately 85-87 days later. After oviposition, nest guarding by females lasts up to two weeks, and involves aggressive interactions, including threat displays, biting, and chasing. Clutch size averages 17 eggs (range 16-20). Hatching success varies from 0 to 100% and appears to be related to maternal body size.
The northeastern portion of the Hellshire Hills has been totally degraded, and much of the land in this section is now virtually barren. Along the north-central border, the charcoal burners have moved 2-3km into the forest, and are approximately 1.5km from the two known nesting sites. Along the south coast, charcoal burners have cut some of the coastal forest, although they have not yet expanded their activities northwards into the limestone karstland. The central and most of the western sections of the Hellshire Hills are still covered with little disturbed, primary tropical forest. However, even in intact forest, iguanas are vulnerable to pressure from exotic predators, especially dogs. In moderately exploited sections of the forest, many trees survive, and there is a rapid regrowth of shrubs and small trees. Such areas might still provide habitat for the iguanas if pressure from exotic predators could be controlled (Vogel et al. 1995).
The most promising site for the establishment of a new subpopulation in the wild appears to be Great Goat Island, where a population of iguanas had survived until at least the late 1940s. However, the numerous goats on the island would have to be removed, and the ground vegetation given an opportunity to recover before any release could take place. At the same time, the island could be rendered mongoose free. The removal of goats would have to be carefully negotiated with the goat owners who live in a nearby fishing village. Other potential release sites include Little Goat Island and the Portland Ridge area, which like the Hellshire Hills retains extensive areas of relatively undisturbed dry forest.
One of the most significant pressures on the remaining population in areas of intact forest is exotic predators, including mongooses, cats, stray dogs, and possibly feral pigs. Mongooses are very common throughout the Hellshire Hills and several observations suggest that they at least occasionally prey on iguana eggs. During the nesting season, they show vivid interest in iguana trial diggings. Mongooses probably prey heavily on hatchlings and young juveniles as well, but few data exist. Cats, which also prey on juveniles, have been observed at various locations in the Hellshire Hills, including nesting areas. The dogs used to hunt feral pigs are of particular concern, as they are able to take even adult iguanas (Woodley 1980). Although feral pigs have not been observed disturbing iguana nests in the Hellshire Hills, evidence from Mona Island suggests that they are potentially important egg predators (Wiewandt 1977).
Another significant problem is the burning of the forest for charcoal production, a local industry that provides income to some 10,000 Jamaicans. Approximately a third of the Hellshire Hills is badly degraded as a result of this enterprise. Short-term management policies have involved establishing good personal relationships with the burners and trying to convince them to move east or west, away from iguana populations and sensitive areas in the center of the Hellshire Hills. Longer term solutions aim at establishing specified buffer zones with low-scale, sustainable charcoal production. Development projects proposing large scale limestone mining and human settlements also threaten the eastern half of the Hellshire Hills. Although a few localized limestone quarries might have only limited impact on the iguanas and their habitat, the new roads that would be constructed to facilitate the mining process would undoubtedly allow charcoal burners, pig hunters, and other forest users to migrate further into the forest.
Current conservation programs
Although most of Jamaica's remaining ecologically important forests, including the Hellshire Hills, are owned by the government and protected by law under the Forestry Act of 1937, the act has received little enforcement. Burning of wood to produce charcoal, slash and burn agriculture, and other destructive uses of the forest still progress. The Hellshire Hills is currently under evaluation as a potential site for a new national park (Jamaica Conservation and Development Trust 1992). To provide interim protection to the area until national park status can be achieved, the Natural Resources Conservation Authority has been petitioned requesting that the Hellshire Hills be declared a protected area under the NRCA Act of 1991. Designation of a protected area would represent a promising legal instrument to prevent the expansion of large-scale development projects in the Hellshire Hills.
Following the rediscovery of the species in 1990, a local Jamaican Iguana Research and Conservation Group comprising representatives from the University of the West Indies, the Natural Resources Conservation Authority, Hope Zoological Gardens, and the Institute of Jamaica was formed. The group carried out an initial field survey during which 23 sightings representing at least 15 different individuals were made (Vogel and Kerr, in press). In addition, a number of signs were found including fecal pellets, tail impressions, and pieces of shed skin. Since then, the group has continuously monitored the two known nesting sites and witnessed each nesting season (Vogel 1994). Each year, about eight females are known to have deposited eggs. A detailed study of the natural history of the species is currently being carried out by Richard Nelson, a postgraduate student in the Department of Zoology, University of the West Indies. His work includes a systematic assessment of the Hellshire Hills habitat, as well as fieldwork on feeding habits, home range use, migration patterns, and reproductive biology.
To devise a comprehensive plan for the recovery of the Jamaican iguana in the wild and to draw international attention to their conservation needs, an IUCN-sponsored workshop was held in Kingston in 1993 (CBSG 1993). The goals of the workshop were to use computer modelling techniques to systematically evaluate the threats to iguana populations and how they might be mitigated through various management strategies, and to heighten awareness about the importance of conserving the biodiversity of the Hellshire Hills. After several computer simulations were run under a variety of scenarios, it became clear that the current level of mortality of juvenile iguanas in the wild was too high to permit survival of the population. This led to recommendations for a headstarting program, in which 50% of the young from wild nests were brought into captivity for up to four years. Once these individuals have attained large enough body size to avoid mongoose predation, they will be acclimated to natural foods and local conditions and released into managed areas within the Hellshire Hills. Initial pilot releases in 1997-1999 have involved subadults out-fitted with radiotransmitters so that their movements patterns and survivorship rates can be carefully monitored.
A program to rear a group of approximately 100 captive juveniles for headstarting is underway at Hope Zoological Gardens in Kingston under the direction of curators Rhema Kerr and Nadin Thompson. In addition to providing a safe environment for juveniles to grow, the zoo is sponsoring studies of juvenile nutrition, social interactions, thermoregulation, and daily activity patterns (Gibson, 1993). The zoo also has plans to develop an exhibit on dry tropical forest ecosystems which highlights the native plant and animal species of the Hellshire Hills.
In 1994, an ex situ captive population was initiated with the importation of 12 individuals to three U.S. institutions (Indianapolis Zoo, Fort Worth Zoo, Gladys Porter Zoo). In 1996, this group was supplemented by a second importation of 12 individuals to the San Diego Zoo (Center for Reproduction of Endangered Species), the Central Florida Zoo, and the Sedgwick County Zoo. Genetic studies carried out by S. Davis have insured that the captive breeding nucleus represents as many founders as possible, thus sampling a diverse cross-section of the wild gene pool. With successful propagation in the U.S., the program will expand to other facilities. Once a target population of 200 is achieved, individuals will be returned to Jamaica for headstarting to assist recruitment into the wild population. As a further safeguard against extinction, captive-reared iguanas may also ultimately be used to establish satellite populations on the Goat Islands provided they can be rendered free of predators.
Critical conservation initiatives
- Designation of the Hellshire Hills as a protected area, and ultimately as a national park.
- Prevention of further population decline through access restrictions, regular patrolling, removal of dogs, and protection of nest sites and hatching young.
- Establishment of sustainable forest use programs in specific buffer zones with low-scale, sustainable charcoal production.
- Exploration of other traditional non-invasive uses of the forest, including collection of medicinal plants, and fishing and crab hunting in coastal areas.
- Promote recovery of the iguana population through predator control.
- Continue Hope Zoo headstarting program and tracking of released radiocollared individuals in the Hellshire Hills.
- Conduct field research, including habitat assessment, feeding ecology, home range use, migration patterns, reproduction, and survivorship.
- Develop an education program in which schools are visited and the importance of iguana conservation is communicated to local people. Programs could initially be concentrated in the Hellshire Hills but should eventually include Kingston and surrounding communities.
- Establish an iguana sanctuary on Great Goat Island following mongoose eradication, removal of goats, and restoration of vegetation.
Note: A portion of the material presented in this species account was adapted from a previously published work (Vogel et al. 1996).
Department of Life Sciences
University of the West Indies
Kingston 7, Jamaica
Tel: (876) 927-1202
Fax: (876) 927-1640
Natural Resources Conservation Authority 53 1/2 Molynes Road
Kingston 10, Jamaica
Tel: (876) 923-5155 or 5125
Fax: (876) 923-5070
Department of Herpetology
Fort Worth Zoo
1989 Colonial Parkway
Fort Worth, TX 76110 USA
Tel: (871) 817-7431
Fax: (871) 817-5637