|Rhinoceros iguana, Cyclura cornuta|
Cyclura is a genus of lizards from the family Iguanidae. Members of this genus are known as "cyclurids" or more commonly as rock iguanas and only occur on islands in the West Indies. Rock iguanas have a high degree of endemism, with a single species or subspecies restricted to individual islands.
- Turks and Caicos rock iguana, Cyclura carinata
- Jamaican iguana, Cyclura collei
- Rhinoceros iguana, Cyclura cornuta
- Northern Bahamian rock iguana, Cyclura cychlura
- Grand Cayman blue iguana, Cyclura lewisi
- Cuban iguana, Cyclura nubila
- Anegada ground iguana, Cyclura pinguis
- Ricord's iguana, Cyclura ricordi
- San Salvador iguana, Cyclura rileyi
Rock iguanas most often inhabit subtropical areas of West Indian dry forest biomes characterized by eroded limestone and sparse vegetation ranging from only moderately dry acacia forest to much drier mesquite and cactus habitats. These are nonvolcanic islands made up of heavily eroded limestone which form natural caves that the iguanas use as retreats.
Diet and longevity
All rock iguanas are herbivorous, consuming leaves, flowers, berries, and fruits from different plant species. A study in 2000 by Allison Alberts of the San Diego Zoo revealed that seeds passing through the digestive tracts of rock iguanas germinate more rapidly than those that do not. These seeds in the fruits consumed by cycluras have an adaptive advantage by sprouting before the end of very short rainy seasons. The iguanas are an important means of distributing these seeds to new areas (particularly if females migrate to nesting sites) and, as the largest native herbivores of many island ecosystems, they are essential for maintaining the balance between climate and vegetation. Their diet is very rarely supplemented with insect larvae, crabs, slugs, dead birds, and fungi; individual animals do appear to be opportunistic carnivores.
Like other herbivorous lizards, the rock iguanas are presented with a special problem for osmoregulation: plant matter contains more potassium and has less nutritional content per gram than meat so more must be eaten to meet the lizard's metabolic needs. Unlike mammals, reptile kidneys cannot concentrate urine to save on water intake. Instead reptiles excrete toxic nitrogenous wastes as solid uric acid through their cloaca. In the case of the rock iguana which consumes large amounts of vegetation, these excess salt ions are excreted through their salt gland in the same manner as birds.
The record for the longest lived captive-born rock iguana is held by a Lesser Caymans iguana, which lived for 33 years in captivity.
A blue iguana captured on Grand Cayman in 1950 by naturalist Ira Thompson was imported to the United States in 1985 by Ramon Noegel and sold to reptile importer and breeder, Tom Crutchfield. Crutchfield loaned this iguana to the Gladys Porter Zoo in Brownsville, Texas in 1997. The lizard was named Godzilla by the zoo staff and was kept until his death in 2004. Thompson estimated the iguana to be 15 years of age at the time of its capture. This lizard may have been the word's longest-living recorded lizard at 69 years of age, having spent 54 years in captivity.
All speciesof Cyclura are sexually dimorphic; males are larger than females, and have more prominent dorsal crests as well as larger femoral pores on their thighs, which are used to release pheromones.
Although the particulars vary slightly among species and subspecies, the rock iguanas reach sexual maturity at three to seven years of age. Females become sexually mature at two to five years of age. Males can be highly territorial with the notable exception of the Exuma Island iguana. Mating takes place at the beginning of or just prior to the first rainy season of the year (May to June) and lasts for two to three weeks. Females lay from 2 to 34 eggs, with an average clutch size of 17 within 40 days. Females of most species guard their nests for several days after laying their eggs, and incubation lasts approximately 85 days. It has been noted that Cyclura eggs are among the largest lizard eggs produced in the world.
Every species and subspecies of rock iguana is endangered. Nine of these taxa are Critically Endangered, meaning there are fewer than 250 of each species or subspecies left in wild populations and in danger of Extinction, four taxa are endangered and three species have been identified as Vulnerable, one species is believed to be extinct in the wild. In addition to small numbers typical of endemic island-dwelling animals, wild populations of these lizards are directly and indirectly impacted by land development, overgrazing by domestic and feral livestock and predation by humans and feral mammals such as hogs, cats, rats, dogs, and mongooses.
In 1990, the American Zoo and Aquarium Association (AZA) designated the genus Cyclura as their highest priority. Their first project was a captive breeding program for the Grand Cayman iguana, which at the time was the most critically endangered of all the species of Cyclura.
The Indianapolis Zoo is involved in research and conservation of all 16 taxa of West Indian iguanas. This includes collaborative work on establishing baseline biological values in captive and wild iguanas, and scientific investigation, conservation efforts, field research and captive breeding programs. The Indianapolis Zoo has been involved in the Dominican Republic for almost ten years and will continue its research and conservation efforts with the Ricord's iguana.
The project's goals are:
- to work with the Ricord’s Iguana Recovery Group to implement the ISG’s Species Recovery Plan.
- to conduct a census of iguanas on Isla Cabritos, Dominican Republic.
- to determine vitamin D status of captive West Indian iguanas at the Zoo before and after exposure to sunlight.
- to continue to develop long-term captive breeding programs for Grand Cayman Island Blue iguanas and Jamaican iguanas at the Indianapolis Zoo.
- to work in partnership with ZOODOM (the national zoo of the Dominican Republic) to develop a long-term captive breeding and husbandry program for Ricord’s iguanas.
- to develop an education program for West Indian iguanas and their habitats.
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