The Cayman Island blue iguana's dusky-blue and gray coloration with cross bands that are often barely visible provides great camouflage among the rocks and scrub they inhabit.
This species of “rock iguana” can exceed 5 feet (1.5 meters) in length (nose to tail tip) and can weigh more than 25 pounds (11 kilograms). These heavy-bodied lizards are the Grand Cayman’s largest native land vertebrate.
Cayman Island blue iguanas are found only on Grand Cayman Island. They prefer dry, rocky forests in coastal areas, which may contain cactus and other thorny plants. These lizards may also be found in scrub woodlands, semi-deciduous forests and dry-to-subtropical, moist forests. Young lizards may climb, but these ground-dwelling reptiles will seldom climb as adults.
The Grand Cayman blue iguana’s diet consists primarily of varied plant life. These lizards may also feed on the occasional insect or snail. At the Smithsonian’s National Zoo, these lizards are fed a wide variety of leafy greens and other vegetables, including kale, carrots and sweet potatoes.
Grand Cayman blue iguanas are sexually mature between 4 to 9 years of age. The breeding season kicks off in March when males begin to display their bright blue colors and spar with other males to claim the territory in which they will breed. Female iguanas are most receptive to breeding in late April and early May, with the most concentrated breeding occurring during the first weeks of May.
After copulation, the female digs a nest cavity in the sand to lay her eggs. These burrows may tunnel 3 feet (.9 meters) before reaching the nest chamber. Females can lay as many as 20 eggs, and these eggs are usually laid between late June and August. Once the female deposits the eggs, she covers them with soil. The incubation temperature is about 84 to 88 degrees Fahrenheit (29 to 31 Celsius). The babies will hatch 65 to 100 days later and are approximately 7 inches (18 centimeters) long and quite active at birth.
The Cayman Island blue iguana appears to be a long-lived species. Their life span in the wild is not precisely known, but one female in human care lived to be at least 69 years old.
Once listed as critically endangered, Grand Cayman blue iguanas were reassessed in 2012 by the IUCN and downlisted to endangered. With ongoing conservation actions, the population is expected to continue to increase. However, the lizard’s small range of occurrence—just 6 square miles (15.6 kilometers)—reflects that the species is now effectively restricted to managed, protected areas. The surrounding and intervening land, once also occupied by iguanas, is inexorably declining in quality as roads, housing and other human infrastructure expand, bringing associated invasive predators.
Feral and free-roaming dogs and cats kill these iguanas and have been shown to be capable of causing local extinction of other Cylura species. Rats have also been observed to cause severe injury or mortality to Grand Cayman blue iguana hatchlings. Both cats and rats have been observed throughout all areas where these iguanas occur, and in 2002, dogs were seen in areas that had supported nesting iguanas as recently as 1993.
A large breeding population of green iguanas, Iguana iguana, from Central America has become established on Grand Cayman and poses a direct threat to the blue iguana. Green iguanas out compete native iguanas for resources. Despite eradication efforts, they continue to reproduce and expand into greater territory on the island at an alarming rate.
Traditional fruit farms have been converted to grassland for cattle grazing on a large scale over the last decade. The loss of fruit trees and herbaceous browse, combined with soil compaction, has drastically reduced the extent of suitable habitat for the iguanas. Increasingly, land is being converted for human residential purposes, increasing the presence of rats, cats and dogs—known predators of the Grand Cayman blue iguana.
Vehicular roads that serve farms in inland residential subdivisions have brought traffic into remnant iguana areas, leading to an increase in road-killed animals. Although the blue iguana is protected under local legislation, occasional illegal captures do occur.
The Blue Iguana Recovery Program (under the auspices of the National Trust for the Cayman Islands) is successfully breeding blue iguanas, rearing them to two years old and releasing them into the Queen Elizabeth II Botanic Park on Grand Cayman. This restored population began breeding in 2001. Currently, nests laid in the Park are collected and the eggs incubated to give hatchlings a head start. In the long term, the program seeks to expand this successful pilot project by establishing a large protected area where a population of 1,000 iguanas can be restored.