The blue iguana (Cyclura lewisi), also known commonly as the Grand Cayman ground iguana, the Grand Cayman blue iguana, and the Cayman Island rock iguana, is an endangered species of lizard in the family Iguanidae. The species is endemic to the island of Grand Cayman. It was previously considered to be a subspecies of the Cuban iguana, Cyclura nubila, but in a 2004 article Frederic J. Burton reclassified it as a separate species because, according to him, the genetic differences discovered four years earlier between the different C. nubila populations warranted this interpretation. The blue iguana is one of the longest-living species of lizard (possibly up to 69 years).

The preferred habitat for the blue iguana is rocky, sunlit, open areas in dry forests or near the shore, as the females must dig holes in the sand to lay eggs in June and July. A possible second clutch is laid in September. The blue iguana's herbivorous diet includes plants, fruits, and flowers. Its color is tan to gray with a bluish cast that is more pronounced during the breeding season and more so in males. It is large and heavy-bodied with a dorsal crest of short spines running from the base of the neck to the end of the tail.

The blue iguana was possibly abundant before European colonization, but fewer than 15 animals remained in the wild by 2003, and this wild population was predicted to become extinct within the first decade of the 21st century. The species' decline is mainly being driven by predation by cats and dogs, and indirectly by reduction in suitable habitat as fruit farms are converted to pasture for cattle grazing. Hunting could have also played a role in their decline. Since 2004, hundreds of captive-bred animals have been released into a preserve on Grand Cayman run by a partnership headed by the Durrell Wildlife Conservation Trust, in an attempt to save the species. At least five non-profit organizations are working with the government of the Cayman Islands to ensure the survival of the blue iguana.

Etymology and taxonomy

The specific name, lewisi, commemorates the surname of the scientist who collected the holotype of this species, Charles Bernard Lewis.

The closest relatives of the blue iguana are the Cuban iguana (Cyclura nubila) and the Northern Bahamian rock iguana (C. cychlura). The blue iguana can be genetically distinguished from the subspecies found on Little Cayman and Cayman Brac known as C. nubila caymanensis, although it can interbreed with this subspecies and produce fertile offspring. Albert Schwartz and Richard Thomas reclassified it as C. nubila lewisi in 1975, making it a subspecies of the Cuban iguana. but he is mistaken. After separating this population taxonomically from the other Cayman Islands rock iguanas, Burton proposed a set of new vernacular names for the population in 2004: Grand Cayman blue iguana, Cayman blue iguana or for local colloquial use he proposed the simple abbreviated blue iguana.

Description

left|thumb|Blue iguana in forest off Wilderness Trail in [[Queen Elizabeth II Botanic Park, Grand Cayman]] An example of island gigantism, the blue iguana is the largest native land animal on Grand Cayman with a total nose-to-tail length of and weighing as much as . This is among the largest species of lizards in the Western Hemisphere. The mature male's skin color ranges from dark grey to turquoise blue, whereas the female is more olive green to pale blue. Young animals tend to be uniformly dark brown or green with faint darker banding. Its distinctive black feet contrast with its lighter overall body color. The blue iguana's eyes have a golden iris and red sclera. males are larger and have more prominent dorsal crests as well as larger femoral pores on their thighs, which are used to release pheromones. Sometimes the Lesser Caymans iguana, C. nubila caymanensis, has been found on Grand Cayman. Blue iguanas released into the Queen Elizabeth II Botanic Park on Grand Cayman were radiotracked in 2004 to determine the home range for each animal. Females were found to occupy territories of and males an average of with overlap in common territories, indicating that they choose to maintain a population density of four to five animals per hectare. Although not known to be arboreal, it has been observed climbing trees and higher. The diet is very rarely supplemented with insects, crabs, slugs, and fungi. Crutchfield donated Godzilla to the Gladys Porter Zoo in Brownsville, Texas in 1997 and the lizard remained there until its death in 2004. Thompson estimated Godzilla to be 15 years of age at the time of his capture.

Reproduction

Mating occurs from May through June. A clutch of 1 to 21 eggs is usually laid in June or July depending on the size and age of the female, in nests excavated in pockets of earth exposed to the sun. Several exploratory nests are begun before one is completed. Surveys in 2003 indicated a total population in the range of 5–15 individuals. In April 2007, after another large-scale release, there were 299 blue iguanas living in the wild, with hundreds more being raised in captivity on Grand Cayman.

International trade in the species is regulated due to its listing on Appendix I of the Convention on International Trade in Endangered Species. No direct negative consequences on the blue iguana due to this introduction are known, but the mere presence of the green iguana confuses public attitudes and understanding.

In 2008, six blue iguanas were found dead in the preserve within Queen Elizabeth II Botanic Park on Grand Cayman. The iguanas were apparently killed by human vandals armed with knives and two of the slaughtered animals were gravid females about to lay eggs.

The wild population of blue iguanas had been reduced from a near island-wide distribution to a non-viable, fragmented remnant. Their first project was an in situ captive breeding program for the blue iguana.

In October 2006, hatchlings were released into the wild for the first time to boost the species and help bring them back from the brink of extinction. Each released blue iguana wears a string of colored beads through its nuchal crest for visual identification at a distance, backed up by an implanted microchip and a high-resolution photograph of its head scales. A rapid numerical increase from a maximum possible number of founding stock is sought to minimize loss of genetic diversity caused by a population bottleneck.

In April 2019, one iguana laid 18 eggs for possible hatching. Any survivals will be the first successful breeding since 2015.

References

  • Blue Iguana Recovery Program (B.I.R.P.)
  • International Reptile Conservation Foundation
  • The National Trust for the Cayman Islands, the B.I.R.P's parent organization
  • International Iguana Foundation