Friday, 29 May 2015

Lizards 14: Rhinoceros Iguana

The last of the lizards in this series is one of the largest lizards in the Americas, the imposing Rhinoceros Iguana Cyclura cornuta. Originating from the island of Hispaniola, which is shared between the countries of Haiti and the Dominican Republic, plus some nearby islands, it is the species of Cyclura most often seen in zoos, plus many more in private collections.

Cyclura species are commonly referred to as rock iguanas, and different species are distributed around the Bahamas and Caribbean. They are usually found in dry limestone areas with caves they can use as shelters from the heat of the sun, and avoid dense vegetation. Many have very restricted ranges, and all the species are of conservation concern, with nine taxa classed as Critically Endangered, and at least one species having become extinct in the 20th century.
Although young Rhinoceros iguanas can climb reasonably well, adults are terrestrial as a result of their large size (a large male can be 1.4m long and weigh 9kg). They are diurnal, patrolling their territories in their search for food. This is almost entirely vegetation, although they will also take crabs out of rock pools, scavenge dead fish from the tideline, or opportunistically take smaller animals or insects.

Iguanas are potential prey for many predators. Natural enemies would be birds of prey, especially for hatchlings, but large snakes would also be a threat. Unfortunately in many parts of the Caribbean they were also targeted by people for eating, and at least one species, the Jamaican Rock Iguana C.collei believed extinct as a result of this and also as a result of the introduced Indian Mongoose and feral pigs, which ate eggs and young. The Jamaican Iguana was rediscovered in 1990 and there is a conservation program in place to try to preserve the species.
The breeding season commences with the first rains, usually around May. Females dig a deep burrow where they lay a clutch of anything from 2 to 34 eggs, depending on the size of the female.  For some days after laying the female guards the nest site, probably to prevent other females from digging in the same place and so digging up their clutch. Incubation takes around 85 days, and the young are over 30cm long when they hatch. The hatchlings take several years to reach maturity, males usually around 5 years with females somewhat less. Lifespan is well over 30 years, possibly much more. “Godzilla”, a Grand Cayman Blue Iguana is on record as living in captivity to well over 50 years. As it was caught as an adult, it may have been at least 69 years old when it died in 2004.

Although classed by the IUCN as Vulnerable, Rhinoceros Iguanas are at the low end of risk compared to most of their relatives. With restricted ranges on densely populated islands, introduced predators, and tourist developments of the beaches where they often prefer to nest, many are classed as Critically Endangered. With protection however they can prove reasonably prolific in captivity. For example, the total population of Grand Cayman Blue Iguanas C.lewisi was down to only 12 in 2004, and today it is up to over 700 and has been upgraded from Critically Endangered to Endangered status.
The Rhinoceros iguanas at Bristol have bred successfully, with the young being sent to other collections. With their long lifespans and space in collections preferred for more threatened taxa however, there is no need to breed more for the present.

This brings to an end this survey of the Bristol Zoo lizard collection. Next time, I will start a review of some new arrivals in the collection.

(Images of C.collei and C.lewisi from Wikipedia, C.cornuta are mine)

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