Lesser Antillean iguana
Iguana delicatissima

By Mark Day, Michel Breuil and Steve Reichling

Description

The Lesser Antillean iguana attains a smaller overall size than its only congener the common iguana (I. iguana), with males reaching 430mm SVL (3.5kg) and females 390mm SVL (2.6kg, gravid). Lesser Antillean iguanas are relatively stout, and in combination with body color and some convergent behavior, bear a superficial resemblance to rock iguanas. The Lesser Antillean iguana can be readily distinguished at any age from the common iguana by the absence of an enlarged subtympanic plate. The two species can also be distinguished by dark barring on the tail of common iguanas, absent on the tail of Lesser Antillean iguanas. The only exceptions are hybrids found on Les Iles des Saintes and Basse Terre, Guadeloupe. The genus Iguana is distinguished morphologically from Cyclura by the presence of gular spikes on the dewlap, and its continuous dorsal crest, which in Cyclura is divided into distinct nuchal, dorsal, and caudal regions.

Adult Lesser Antillean iguanas exhibit sexual dimorphism in a number of characters. Males possess enlarged dorsal crest scales, especially in the nuchal region, enlarged gular spikes on the dewlap, and greater development of the occipital scales. All dimorphic features give an exaggerated lateral profile which is accentuated fully during territorial disputes. In dominant males, both body and tail are dark gray. When males become reproductively active, the jowls flush pink and the fleshy occipital scales develop a pale blue color. Observations of captive individuals indicate that when two males are kept together as part of a group, one will become dominant. If the dominant male is later removed, the subordinate male will then acquire the dimorphic and dichromatic characteristics typical of dominance. Sexual dichromatism is distinct in the more mesic southern part of the species' range, but is much less pronounced in the xeric subpopulations on limestone islands where large females eventually develop an overall gray color.

Hatchlings and juveniles are bright green. White flashes on the jaws and shoulders are linked, and these together with usually three vertical white bars on the flanks form disruptive coloration. Dorsal chevrons of juveniles darken in response to stress and improve camouflage, and as a result body color ranges from green to green with brown flashes. Ontogenetic changes result in the gradual loss of white flashes, and a significant reduction in color change ability. Head coloration lightens until both sexes have pale heads and uniform green bodies. Early in development, the tail begins to turn brown at the tip and becomes progressively darker rostrally.

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.

Distribution

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

1. Anguilla
2. St. Martin
3. St. Eustatius
4. St. Barthélemy, including Ilet au Vent, east of Ile Fourchue
5. Antigua
6. Guadeloupe, including Basse Terre, La Désirade, Iles de la Petite Terre, and Les Iles des Saintes (possibly extinct)
7. Commonwealth of Dominica
8. 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.

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. These population estimates are based subjectively on comparisons of observed density of iguanas and the extent of their range within each island. In qualitative terms, the Commonwealth of Dominica is believed to support the largest single population due to the extent of available coastal habitat and known distribution, while Les Iles de la Petite Terre support the highest population density. However, many populations have been reduced to extremely low levels in very limited areas such that their long-term viability is questionable.

Les Iles de la Petite Terre represent the only stable population throughout the species' range. In La Désirade and the Commonwealth of Dominica where populations are sizeable, there are localized decreases as a result of habitat loss and hunting, but at present these pressures affect a small percentage of the range within each island. In all other cases, populations are believed to be decreasing due to a combination of habitat loss and fragmentation, introduced predators, browsing competitors, or hybridization with common iguanas. Museum specimens and publications indicate that Lesser Antillean iguanas existed historically on Barbuda, Grande Terre (Guadeloupe), Ile Fourchue, Ile Frégate and Ile Chevreau (St. Barthélemy), Marie Galante, Nevis, and St. Kitts, although precise extinction dates are unknown.

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.

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.

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.

Longevity studies have yet to be conducted, but reliable observations of a population acclimated to humans include individuals at least 15 years old. Natural predators of juveniles include snakes (Alsophis spp., Boa constrictor nebulosa), birds (Buteo spp., Falco sparverius), and possibly opossums (Didelphis marsupialis). Teiid lizards (Ameiva fuscata) have been observed predating eggs from nests, although it is unclear if they actively dig to expose them. No known natural predators of adult iguanas have been identified.

The Lesser Antillean iguana is a generalist herbivore, feeding primarily in the morning, with a diet that includes leaves, flowers, and fruits of a wide range of shrubs and trees including Capparis, Eugenia, Hippomane, Ipomea, Opuntia, Solanum, and Tabebuia. Hippomane possesses toxic compounds that render it unpalatable to birds and mammals, but do not appear to affect iguanas. Seasonal variation in feeding ecology exists, with folivory during the dry season shifting to florivory and frugivory during the wet season. Feeding is selective with fresh leaf growth, flower buds, and ripe fruits preferred. Seed dispersal by iguanas may be significant for a number of coastal forest plant species, especially those with large or unpalatable fruits which are not dispersed by small birds or bats. Differences between populations in feeding ecology exist, reflecting local variation in plant species composition (either natural or as a result of introduced browsers). Like its congener the common iguana, the Lesser Antillean iguana has been observed by some to be opportunistically carnivorous (Lazell 1973).

Adult males actively defend small territories, at least during the reproductive period. Most territorial defense consists of headbobbing and laterally compressed profile displays. When in close proximity, side-walking displays give way to head-to-head pushing contests accompanied by arching of the tail. Fighting occurs infrequently, although severe head, limb, and crest damage has been recorded. Courtship is limited and mating is typical of other large iguanids. The Lesser Antillean iguana exhibits a polygynous mating system, with male/female sex ratios ranging from 1:1 to 1:7. Adult females occupy larger home ranges than adult males, and do not defend them. Female home ranges overlap other females and sometimes multiple males. Anecdotal observations suggest a hierarchical structure among females associated with a dominant male. In the wet season, groups of individuals converge upon certain fruiting trees, or those with fresh leaves. In these cases, juveniles of both sexes feed communally, whereas adults feed together only if a single dominant male is present.

Reproduction is timed to maximize hatchlings' ability to feed on nutritionally-rich wet season plant growth and grow rapidly prior to the onset of the dry season. In xeric habitats where seasonal conditions are most marked, reproduction appears to be roughly synchronous (e.g., Petite Terre), whereas more mesic populations are much less synchronous (e.g., in the Commonwealth of Dominica, gravid females can be found from February to August). The breeding season is so prolonged in the Commonwealth of Dominica that more than one clutch per year may be possible. Females migrate to nesting sites outside their normal home range, travelling a mean distance of 460m, up to a known maximum of 900m. As migrating females often pass other active nest sites, natal homing may occur in this species. Nest sites occur in sandy, well-drained soil exposed to prolonged sunlight, with simple 1m long excavated tunnels ending in a chamber sufficient for the female to turn around. Clutch size, which may vary geographically, ranges from 8-18 (mean egg mass 25g), and is strongly correlated with female size. Anecdotal evidence suggests an incubation period of approximately three months.

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.

Habitat

Due to extensive habitat alteration, particularly since European colonization, for agriculture, timber extraction, and housing, little to no coastal habitat remains in its primary state in the Lesser Antilles. The only possible exception is the proposed Réserve Biologique Dominiale de la Montagne Pelée in Martinique. Nevertheless, rapid natural regeneration is characteristic of hurricane-adapted vegetation, such that significant areas of habitat capable of supporting iguanas still exist. Localized clearance or disturbance of land for timber extraction or charcoal production may result in initial displacement of iguanas, with subsequent recolonization accompanying recovery of the vegetation. Lesser Antillean iguanas cannot tolerate large scale clearance. Continuous degradation by free-ranging goats and other herbivores has a slow but serious effect due to the shift in species composition towards a high proportion of plants which are either toxic or unpalatable (Croton, Lantana, Agave). Areas subjected to browsing pressure support significantly lower iguana populations than comparable habitats which are free of introduced browsers.

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.

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.

Lesser Antillean iguanas are impacted by a range of introduced predators. Feral and house cats are believed to be significant predators of juvenile iguanas on Anguilla. On St. Barthélemy, feral predators are few, but adult iguanas are known to be killed by guard dogs that run free within fenced property compounds where iguanas move to feed. Indian mongooses (Herpestes javanicus [=auropunctatus]) were introduced to many islands with the intention of eradicating rats and snakes. Hatchlings and juveniles fall within the prey range of mongooses, and on all islands where mongooses occur, the Lesser Antillean iguana is either extinct or highly threatened. However, it is unclear how significant the impact of the mongoose is compared to other factors.

Free-ranging and feral browsing competitors exist alongside almost all iguana populations, with the notable exceptions of Iles de la Petite Terre and most of the Commonwealth of Dominica. Goat and sheep populations are particularly large, and of most concern on Anguilla, Ilet Chancel, La Désirade, and St. Eustatius, where extensive overbrowsing continues to cause a shift in plant species composition and habitat structure. Lazell (1973) reported that "huge colonies swarm on the Ile Fourchue, Les Iles Frégate, and the Ile Chevreau, or Bonhomme." Subsequently, massive overbrowsing by introduced goats in combination with a series of droughts resulted in the extinction of these St. Barthélemy offshore populations by the early 1990s.

Historically, hunting occurred throughout the range of the Lesser Antillean iguana since the time of the Amerindians. Hunting is now illegal throughout the species' range. However, St. Eustatius has recently experienced dramatic rises in iguana hunting, causing a crash in the population. Increased hunting was linked to the influx of construction workers for the expansion of oil storage facilities on the island, and economic problems caused by changes in European Community regulations. Despite recent local legislation, iguana meat continues to be sold locally and transported to restaurants in nearby St. Martin. Hunting also remains locally prevalent in parts of the Commonwealth of Dominica, where certain populations have experienced rapid unsustainable exploitation.

Hybridization between Lesser Antillean iguanas and common iguanas has now been confirmed through both molecular genetic and morphometric analyses from samples taken in Basse Terre (Guadeloupe) and Les Iles des Saintes. The process appears to occur rapidly. In Les Saintes, Lazell (1973) estimated qualitatively that the two species were equally abundant in the 1960s, and concluded that they occurred sympatrically. Morphometric analysis of specimens collected at that time by Lazell show that in fact hybridization was already progressing. By 1995, less than 10 individuals recognizable as Lesser Antillean iguanas could be located, all of which exhibited intermediate species characteristics. In contrast, the common iguana remains extremely abundant and has extended its range within the archipelago. Invasive displacement through competition and hybridization appears to be the dominant factor in the disappearance of Lesser Antillean iguanas from Les Iles des Saintes, due to the absence of other identifiable environmental changes. The same situation has been documented in Basse Terre (Guadeloupe) and St. Barthélemy, although in both cases it is less advanced. Deliberate introduction and subsequent expansion of common iguanas in Antigua, Martinique, and St. Martin have also been recorded. At present, these are not known to have led to hybridization in Antigua and Martinique, where the two species' distributions remain discrete. In St. Martin, the situation is unclear. Hybridization and aggressive displacement of Lesser Antillean iguanas by common iguanas should be considered potentially serious threats to all remaining populations. In 1995, as a result of Hurricane Luis, at least 12 common iguanas believed to have originated from the Guadeloupe Bank washed up in Antigua, Barbuda, and Anguilla, although most either subsequently died or were killed for food. Nevertheless, this demonstrates that overwater dispersal of iguanas between different islands banks may occur.

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.

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.

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.

Captive Lesser Antillean iguanas are currently held at the Durrell Wildlife Conservation Trust (1.1.1), Memphis Zoo (2.2), and the San Diego Zoo's Center for Reproduction of Endangered Species (1.1). All individuals originate from the Commonwealth of Dominica. Mating has been observed and eggs laid at each institution. Although most eggs have been infertile or non-viable, a single individual was successfully hatched at the Durrell Wildlife Conservation Trust in 1997. As the Dominican population is presently healthy, these individuals and their future offspring should remain in captivity in order to gather husbandry expertise, as well as growth and reproductive data. The long term aim is to gain captive breeding expertise which can then be applied in situ. Captive-bred individuals could be used for reintroduction to offshore islands and other protected areas known to have supported Lesser Antillean iguanas historically, or for restocking depleted populations. Due to considerations of geographic variation, reintroduction should utilize iguanas from the same population or island bank whenever possible.

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.

Priority projects

1. Implement a series of comprehensive population surveys for all populations. The first of these was undertaken in Anguilla in 1997, with support from the U.K. Foreign and Commonwealth Office.
2. Assess the potential of additional satellite islands to become protected areas for maintaining or establishing populations of the Lesser Antillean iguana through reintroduction and/or habitat restoration (Anguilla, Antigua, Guadeloupe, Martinique, St. Barthélemy, St. Martin).
3. Carry out a long-term ecological study of the xeric adapted Lesser Antillean iguana population on les Iles de la Petite Terre, which, because it is free from ongoing habitat destruction, feral predators, and competitors, represents the most dense and least threatened remaining population.
4. Develop regional and national education programs for schools, other residents, and visitors, utilizing a broad range of media to illustrate the plight of the Lesser Antillean iguana and its importance to forest ecosystems. National (Breuil, in press) and regional (Malhotra and Thorpe, in press) herpetological guides can assist in these efforts.

Contact persons

Mark Day
Fauna and Flora International
Great Eastern House
Tenison Road
Cambridge, CB1 2DT
United Kingdom
Tel: 44-1223-578464
Fax: 44-1223-461481
E-mail: marklday@aol.com

Michel Breuil
Laboratoire des Amphibiens et Reptiles
Musée National d'Histoire Naturelle de Paris
25 Rue Cuvier
75005 Paris
France
Tel/Fax: 33-(0)-1-4305-9043
E-mail: mabreuil@club-internet.fr

Steve Reichling
Herpetarium/Aquarium
Memphis Zoo and Aquarium
2000 Galloway
Memphis, TN 38112 USA
Tel: (901) 725-3400
Fax: (901) 725-9305
E-mail: sreichling@memphiszoo.org