About Cyclura lewisi Grant, 1940
Cyclura lewisi, commonly known as the blue iguana, is an example of island gigantism. It is the largest native land animal on Grand Cayman, reaching a total nose-to-tail length of 5 ft (1.5 m) and weighing up to 30 lb (14 kg), making it one of the largest lizard species in the Western Hemisphere. It is the largest species in the Cyclura genus, with a body length of 20–30 in (510–760 mm) and a tail of equal length. Its toes are specially articulated for efficient digging and tree climbing. Mature male blue iguanas have skin color ranging from dark grey to turquoise blue, while females are more often olive green to pale blue. Young blue iguanas are typically uniformly dark brown or green with faint darker banding. When newly hatched neonates first emerge from the nest, they have an intricate pattern of eight dark dorsal chevrons stretching from the neck crest to the pelvic area. These markings fade by the time the animal is one year old, changing to mottled gray and cream before eventually shifting to blue as the iguana reaches adulthood. Adult blue iguanas are typically dark gray, which matches the karst rock of their native landscape. They change their color to blue when in the presence of other iguanas to signal and establish territory, and this blue color is more pronounced in males. The species has distinctive black feet that contrast with its lighter overall body color. Its eyes have a golden iris and red sclera. Blue iguanas are sexually dimorphic: males are larger, with more prominent dorsal crests and larger femoral pores on their thighs, which are used to release pheromones. Males are one third larger in body size than females. The blue iguana is endemic to the island of Grand Cayman. As of 2012, the species' population is found across Grand Cayman, excluding the urban areas of Bodden Town, Gun Bay, Seven Mile Beach, and West Bay. One hypothesis for how the species arrived on the island is that a single gravid female Cuban iguana (C. nubila nubila) drifted across the sea to Grand Cayman, possibly during a storm. The Lesser Caymans iguana (C. nubila caymanensis) is occasionally found on Grand Cayman. Comparison with other Cyclura species in the region strongly suggests that coastal blue iguana populations once existed, but were gradually displaced or extirpated by human settlement and road construction. Currently, blue iguanas only occur inland in natural xerophytic shrubland, and along the interfaces between farm clearings, roads, gardens, and closed-canopy dry forest or shrubland. Inland populations are thought to have been attracted to agricultural clearings and fruit farms, which provide opportunities for thermoregulation, herbaceous food, fallen fruit, and nesting soil, but this exposure has brought blue iguanas into contact with humans and feral animals. Females often migrate to coastal areas to build nests. In 2004, blue iguanas released into the Queen Elizabeth II Botanic Park on Grand Cayman were radiotracked to measure each animal's home range. The study found that females occupied territories of 0.6 acres (2,400 m2), while males occupied an average of 1.4 acres (5,700 m2), with overlapping common territories. This indicates that blue iguanas maintain a population density of four to five animals per hectare. Blue iguanas occupy rock holes and tree cavities; adults are primarily terrestrial. While the species is not known to be arboreal, individuals have been observed climbing trees 15 feet (4.6 m) and higher. Younger individuals tend to be more arboreal. Blue iguanas spend very little of their daytime in a retreat, and only retreat for the day at the end of daylight hours. Mating takes place from May through June. Before copulation, the male performs numerous head-bobs, then circles behind the female and grasps the nape of her neck. He then attempts to restrain the female to maneuver his tail under hers to position himself for copulation. Copulation typically lasts 30 to 90 seconds, and a pair is rarely observed mating more than once or twice per day. Females lay a clutch of 1 to 21 eggs, usually in June or July, with clutch size depending on the female's size and age. Eggs are laid in nests excavated in pockets of earth exposed to the sun. Females begin several exploratory nests before completing a final nest. These nesting burrows range from 16 inches (0.41 m) to over 60 inches (1.5 m) in length, with an enlarged chamber at the end that allows the female to turn around. In monitored nests, the internal temperature remained a constant 32 °C (90 °F) throughout the incubation period, which lasts 65 to 90 days. The eggs of the blue iguana are among the largest laid by any lizard species. Blue iguanas are aggressively territorial starting from around three months of age. In captivity, they typically reach sexual maturity after four years of age.
