Taxonomy. The Grand Cayman Blue Iguana, Cyclura lewisi Grant, is endemic to the island of Grand Cayman. Its closest relatives are Cyclura nubila on Cuba, and Cyclura cychlura in the Bahamas, all three having apparently diverged from a common ancestor at some stage during the last 3 million years.
Status. The Blue Iguana is critically endangered according to the current IUCN Red List. The population is restricted to the east interior of Grand Cayman, where it was reduced to a critically low density prior to the first survey in 1938. The range has contracted significantly over the last 25 years, with many sites once populated now showing no signs of wild iguanas. The most recent comprehensive survey in 2002 indicated a total population in the range 10-25 individuals. By 2005 the unmanaged wild population was considered to be functionally extinct. The species is now the most endangered iguana on Earth.
However, restored free-roaming subpopulations in the QE II Botanic Park and the Salina Reserve now number approximately 290 individuals in total, after a series of releases of captive reared young. The restored subpopulation on the QE II Botanic Park has been breeding since 2001, and the subpopulation in the Salina Reserve began breeding in 2006.
Natural History. While it is likely that the original population included many animals living in coastal environments, the Blue Iguana now only occurs inland, in natural xerophytic shrubland, and along the interfaces between farm clearings, roads and gardens, and closed canopy dry forest or shrubland. The iguanas occupy rock hole and tree cavity retreats, and as adults are primarily terrestrial. Younger individuals tend to be more arboreal.
Like all Cyclura species the Blue Iguana is primarily herbivorous, consuming leaves, flowers and fruits from over 100 different plant species. This diet is very rarely supplemented with insect larvae, crabs, slugs, dead birds and fungi.
Mating occurs in May, and eggs are usually laid in June or July, in nests excavated in pockets of earth exposed to the sun. Individuals are aggressively territorial from the age of about 3 months. Females occupy partially overlapping usage areas of the order of 740m2, while males may occupy larger and more extensively overlapping usage areas, as they age and grow.
Hatchlings are preyed upon by the native snake Alsophis cantherigerus. The adults have no natural predators. The age of sexual maturity is typically 3 years. Natural longevity in the wild is unknown, but is presumed to be many decades (one captive in the USA is known to have died at approximately 69 years of age).
Causes of decline. Habitat destruction is the main factor threatening imminent extinction for this iguana. Land clearance within remnant habitat is occurring for agricultural purposes, road construction and for real estate development and speculation. Conversion of traditional croplands to cattle pasture is also eliminating secondary Blue Iguana habitat.
Invasive mammalian predators are placing severe pressure on the remaining wild population. Free-roaming dogs kill adult iguanas, feral and semi-domestic cats hunt hatchlings and sub-adults, and rats injure and kill hatchings, and may occasionally invade nests. Road kills are an increasing cause of mortality. Trapping and shooting is a comparatively minor concern, but occasional trapping continues despite legal protection and sustained efforts in public awareness.
The Common Iguana, Iguana iguana, has become naturalized in Grand Cayman and now far outnumbers the endemic Blue Iguana. No direct negative consequences affecting the Blue Iguana are yet confirmed, but the situation confuses public attitudes and understanding.