Specialized Iguan Study Group

Critical conservation initiatives

• Implementation of protected areas management plans for designated nature reserves on les Iles de la Petite Terre, Ilet Chancel, and Réserve Biologique Domaniale de la Montagne Pelée.
• Identification and development of protected areas at key sites on major islands which remain, or have the potential to be restored to, important habitat for Lesser Antillean iguanas.
• Development of an inter-governmental agreement, including production of accompanying publicity materials for airports and ports, to reduce or prevent further introduction of common iguanas onto islands supporting Lesser Antillean iguanas.
• Development of a species conservation plan for the Lesser Antillean iguana which would result in the coordinated implementation of both regional and national conservation initiatives. The plan would incorporate, but not be limited to, the priority projects outlined below.

M. Day is undertaking doctoral research (University of Aberdeen and University College of North Wales) on the population biology of iguanas throughout the Lesser Antilles. Aspects of the research include geographic variation using molecular genetic and multivariate statistical techniques, hybridization, home range and habitat use, diet, and ectoparasites. M. Breuil is undertaking ecological research on both species in Guadeloupe, Martinique, St. Barthélemy, and St. Martin. In collaboration with Association pour l'Etude et la Protection des Vertébrés des Petites Antilles, he has begun surveys of the proposed nature reserves within the French West Indies, and is gathering data required for development of a conservation management plan for the proposed protected areas in Guadeloupe and Martinique. A. Alberts is conducting research on variability in the protein composition of femoral gland secretions of Lesser Antillean iguanas and common iguanas at the interpopulation level.

Current conservation programs

The Lesser Antillean iguana is legally protected from hunting throughout its range, but enforcement of these regulations is extremely difficult and therefore limited. Currently, only a single protected area, the Cabrits National Park (Commonwealth of Dominica) contains a small population. Five additional areas, Les Iles de la Petite Terre (Guadeloupe), the Quill and the Boven (St. Eustatius), and Ilet Chancel and the Reserve Biologique Domaniale de la Montagne Pelée (Martinique), are presently proposed as nature reserves which will protect Lesser Antillean iguanas. Additionally, a number of satellite islets around Anguilla, Antigua, Guadeloupe, Martinique, and St. Barthélemy offer significant potential as protected areas. Following suitable legislative protection and ecological restoration, a number of additional islands would be feasible for translocation or reintroduction.

Road casualties occur regularly along coastal roads which bisect iguana habitat in the Commonwealth of Dominica, Basse Terre (Guadeloupe), La Désirade, and St. Barthélemy. In the Commonwealth of Dominica, casualties peak late in the dry season when numerous gravid females are killed while migrating to coastal nest sites and early in the wet season when hatchlings disperse from nests.

Threats

Habitat loss and fragmentation were historically most extensive on the least mountainous islands, which have been systematically cleared for agriculture, especially sugarcane. On these islands, the Lesser Antillean iguana has either become extinct (e.g., St. Kitts, Nevis) or remains only in tiny remnant populations (e.g., Basse Terre, St. Eustatius). As tourism has superceded agriculture in importance, coastal development has further reduced the remaining habitat and significantly affected already-limited communal nest sites.

Habitat

Suitable habitat is currently shrinking, mostly due to development. Exclusion or removal of introduced predators and/or herbivores as part of an ecological restoration program would permit a significant increase in the amount of habitat available. Les Iles de la Petite Terre now support the highest known population density of Lesser Antillean iguanas despite the fact that the islands experienced extensive cultivation and grazing until the early 1960s.

As Lesser Antillean iguanas occur in several different habitats with variable environmental conditions, differences between populations in ecology and natural history exist. In particular, xeric conditions are associated with low-lying coralline limestone islands whereas more mesic conditions occur on mountainous volcanic islands. Xeric scrub is structurally less complex and reaches a lower canopy height than dry scrub or littoral woodland. In these habitats, iguanas exhibit terrestriality frequently, and will readily drop to the ground to escape if disturbed. Terrestrial refugia between rocks or in limestone caverns are used for both escape and sleeping. In more mesic habitats, iguanas are almost exclusively arboreal, feeding in tree crowns 30m or more above the ground and moving by jumping between tree crowns.

Upon emergence from nests, hatchlings disperse into surrounding vegetation. Both hatchlings and juveniles live predominantly among bushes and low trees, usually in thick vegetation offering protection, basking sites, and a wide range of food. With age, they climb higher and utilize larger trees. Sexual maturity appears to be reached at approximately three years, although breeding in males is unlikely to begin at this time due to inability to achieve dominance and defend a suitable territory.

Ecology and natural history

The Lesser Antillean iguana occupies islands of the northern Lesser Antilles from sea level to approximately 300m elevation, and appears to be limited by thermal requirements. The species exists in xeric scrub, dry scrub woodland, littoral woodland, and mangrove, as well as lower altitude portions of transitional rainforest. The condition of these habitats varies from island to island, with Lesser Antillean iguanas able to survive in extremely xeric degraded habitats (<1,000mm annual rainfall) to mesic forests (3,000 to 4,000mm annual rainfall), in the absence of introduced predators or competitors.

Overall population status appears Vulnerable at present due to an estimated population decline of greater than 10% per generation for the last two generations and the fact that only two populations exceed 5,000 individuals. Populations are critical on Antigua, Anguilla, Ilet au Vent, Les Iles des Saintes, St. Eustatius, and St. Martin. Populations on Basse Terre, Ilet Chancel, Martinique, and St. Barthélemy are endangered, estimated at between 250 and 2,500 individuals. Although populations are somewhat larger on Dominica, Iles de la Petite Terre, and La Désirade, they are still considered vulnerable due to habitat alteration and/or the threat of introduction of common iguanas.

Status of populations in the wild

Insufficient data currently prevent accurate estimation of population size for the Lesser Antillean iguana. Formal surveys using standardized transect techniques have only been conducted for Ilet Chancel (population estimate 200-300) and Terre de Bas (Les Iles de la Petite Terre, population estimate 4,000-6,000). Rough population estimates for the remaining islands are based on limited surveys designed predominantly to locate iguanas for morphometric and genetic data collection.

Distribution

Unless indicated, populations refer only to main islands, and do not imply additional offshore populations on islets (Fig. 9).

Anguilla

St. Martin

St. Eustatius

St. Barthélemy, including Ilet au Vent, east of Ile Fourchue

Antigua

Guadeloupe, including Basse Terre, La Désirade, Iles de la Petite Terre, and Les Iles des Saintes (possibly extinct)

Commonwealth of Dominica

Martinique, including Ilet Chancel

Historically, this species is believed to have existed throughout the northern Lesser Antilles, from Anguilla to Martinique, from sea level up to 300m, in xeric scrub, dry scrub woodland, littoral woodland, and lower altitude potions of transitional rainforest.

By Mark Day, Michel Breuil and Steve Reichling

No subspecies are recognized. Analysis of geographic variation using multivariate statistical and molecular genetic techniques is ongoing. Preliminary results indicate a low level of geographic variation, but patterns that correlate with island banks.