April Research colloquium: Rhinos of the Caribbean

This month’s talk was given by John Bendon, an artist working with the Iguana Specialist Group of the IUCN, and was an overview of the magnificent Cyclura ground iguanas of the Caribbean. We have an adult pair at Bristol of one of the largest species, the Rhinoceros Iguana of Haiti and the Dominican Republic, which has a length nose to tail of over 1m and has adult males that can weigh 10kg. Last year, we bred them for the first time, producing 17 young of which 5 can be seen on-show and the remainder are being held off-show for growth studies.


There are currently at least 17 distinct species and subspecies of ground iguanas recognized, but in reality every small cay (flat coral island) or larger island harbours a local form that can often be identified, at least by DNA work. This is still only a fraction of the diversity that may have formerly existed – as with giant tortoises, human predation combined with introduced pigs, cats, dogs, and mongooses has called local extinctions, especially on small islands. At least one species, the Jamaican Iguana Cyclura collei, was believed extinct until rediscovered in the 1990’s, and despite extensive conservation work still only has a population of perhaps 100 adults in the wild, with few young surviving.

Cyclura vary in size and colouration from island to island, with the smallest only about .5m long nose to tail, whereas the largest, the Grand Cayman Blue Iguana, has a length of 1.5m and a maximum weight of 14kg. They are also long lived, with a record of a Grand Cayman iguana living to be 67 years old. They are almost entirely vegetarian, eating herbaceous weeds, leaves of shrubs, and some fruits, depending on what is available, and will also scavenge the tide line or take crabs from rock pools.

Much of the talk was taken up with report on the Mona Island Iguana, a subspecies of Rhinoceros Iguana. The behaviour appears to be quite complex, with individuals using a well known home range. Males have a territory overlapping several females, but territory boundaries change over time as animals mature and vegetation changes.

One potentially serious problem is that a high percentage of Mona Island iguanas are partially or entirely blind. The reason for this is not at all clear, and much work is being done, but it was suggested in the meeting that one possible cause is invasive fire ants. These are known to cause blindness in domestic pets, so could easily have a similar effect on the iguanas.

Conservation work for Cyclura involves a range of possible options. Captive breeding programmes are in operation for most of the species, and protection in the wild by means of reserves is useful in some areas. “Headstarting”, which involves keeping hatchlings for a year or two until they have grown large enough to be immune to cats or other introduced predators, is also in operation.

Cyclura mostly do well in captivity if their requirements are met. They will eat a variety of leafy vegetables and fruits, as for the more commonly kept Green Iguanas, but they have high UV requirements and need a lot of space. Ours live in a modified conservatory with our Aldabra Giant Tortoises, and have access in the warmer part of the year to a sheltered outside paddock with a wall at the back which has ledges they can climb up to bask. I like seeing them outside – in general the only reptiles you see in the open air in the UK (other than natives) are various tortoises, and I feel that potentially several other larger lizard species might do well with outside access, such as monitors or some chameleons.

This is only a brief overview of course – for more on these animals check out the IUCN Iguana Specialist Group website at http://www.iucn-isg.org/index.php The newsletters and reports have a great deal of useful information.

(picture from wikipedia)