Rhinoceros iguana (Cyclura cornuta)

Also known as: horned ground iguana
  
French: Cyclure Cornu, Iguane Cornu, Iguane Terrestre Cornu
KingdomAnimalia
PhylumChordata
ClassReptilia
OrderSquamata
FamilyIguanidae
GenusCyclura (1)
SizeMale length (excluding tail): up to 56 cm (2)
Female length (excluding tail): up to 51 cm (2)
Male weight: up to 10 kg (2)

Classified as Vulnerable (VU) on the IUCN Red List 2006 (1), and listed on Appendix I of CITES (3). Subspecies: the rhinoceros iguana (C. c. cornuta) is classified as Vulnerable (VU), and the Mona Island iguana (C. c. stejnegeri) is classified as Endangered (EN) on the IUCN Red List 2006 (1).

The common name of this massive, heavily built iguana is inspired by the several enlarged, horn-like scales on its snout, resembling the horns of a rhinoceros (4) (5). These are more prominent in males (4) (5), and are accompanied in both sexes by two distinctive, round pads of fatty tissue crowning the head (2) (6). Rough scales cover the body, which is uniformly greyish-brown, olive-green (4) (5), or even black in colour, lacking the bright colours that adorn several other iguana species (2). This sombre colouration helps camouflage the animal against the rocks and scrub of its habitat (6).

The nominate subspecies, C. c. cornuta, is found in the West Indies on Hispaniola (Haiti and the Dominican Republic) and surrounding islands. As its common name implies, the Mona Island iguana (C. c. stejnegeri) subspecies is endemic to the remote island of Mona, a small 11 by 7 km island situated midway between Puerto Rico and Hispaniola (2). Another closely related species or subspecies (scientific opinions vary) was found on Navassa Island, but is now believed extinct (4).

Rhinoceros iguanas are terrestrial reptiles that prefer dry, rocky terrain in coastal areas, but also inhabit scrub woodlands, semi-deciduous forests and dry to subtropical, moist forests (2) (6). Although primarily coastal, human expansion has forced many populations to retreat further inland (4). Subtropical Mona Island is vegetated with an open canopy forest of short, seasonally deciduous trees, shrubs, cacti and bromeliads (2).

Rhinoceros iguanas are active during the day and, like many reptiles, regulate their body temperature by basking in the sunshine to warm up and seeking shade when too hot (2) (4). At night they retreat to caves, hollow tree trunks, burrows and rock crevices. These sheltered rest areas are so important that males will actively defend territories containing retreats attractive to females (2).

Breeding occurs once a year, either just before or at the start of the first rainy season (2), around April to May (4) (6). Approximately 40 days after mating, usually between June and August (4) (6), females lay a clutch of two to 34 eggs (average of 17) into a nest cavity dug in the sand (2). Females may guard the nest for a number of days after laying, and the young hatch after 85 days (2). The young rhinoceros iguanas are independent from hatching, with no parental investment as they grow (4). Although longevity records are not available for the rhinoceros iguana, large rock iguanas are amongst the longest lived lizards in the world, and most species live for several decades and can take years to reach maturity (2).

This iguana is primarily herbivorous, feeding on a variety of leaves, fruits, flowers, and seeds (2) (4). However, insects, land crabs and carrion (especially dead birds and fish) will occasionally be taken (4), and caterpillars are known to be part of the diet on Mona Island (2). Young iguanas in particular are thought to feed on insects and other small animals (4).

The main threat facing this species is habitat loss as a result of logging for hardwoods, exploitation for charcoal production and fuel wood, livestock grazing, agriculture and mining of limestone. In the Dominican Republic around 35% of suitable habitat has been totally lost; of the remaining habitat, 75% is disturbed and the situation is much worse in Haiti (2). Other threats include predation by dogs, cats, pigs, and mongooses, and illegal hunting by humans for food is a very serious problem in parts of Haiti, a country mired in poverty (2) (4). International trade in wild rhinoceros iguanas has been controlled since 1987 in the Dominican Republic, but not in Haiti (2).

Introduced exotic species pose the most serious threat to the subspecies on Mona Island, which has evolved in the near absence of predators and is therefore ill-equipped to cope with the dangers they now pose. In particular, the combined effect of pigs consuming eggs and cats preying on young has resulted in the present scarcity of juveniles on the island. Feral goats may also be having a damaging impact by gathering in sinkhole depressions on Mona's plateau where the iguana nests, and also through intense browsing pressure affecting the vegetation of the island. Although there are no permanent settlements on the island, Mona attracts many recreational pursuits, including camping, fishing, swimming, scuba diving, beach combing, exploring, and hunting. Most of these activities are concentrated along the island's sandy coastal terraces and within sinkhole depressions, areas of critical importance for iguana nesting. An additional recent concern is the emergence of an unidentified disease or parasite that causes blindness in the iguana, which in turn appears to affect the iguana’s ability to feed (2).

International trade in the rhinoceros iguana is controlled by its listing under Appendix I of the Convention on International Trade in Endangered Species (CITES). Most populations occur within protected areas in the Dominican Republic, and the species is protected under national wildlife laws. Although enforcement of these laws has improved in recent years, habitat destruction remains a problem and illegal hunting for food and for the pet trade continues. Sadly, the situation looks bleaker in Haiti, where there are no formal protected areas supporting this species and enforcement of any existing wildlife laws is unlikely. There are a large number of rhinoceros iguanas in captive breeding programmes around the world, and some have even included experimental reintroductions of captive-bred young to several protected areas in the southwest Dominican Republic. Nevertheless, the conservation of existing wild populations must remain a priority. Suggested future needs include the establishment of local educational awareness campaigns to try to reduce illegal hunting, the strengthening and enforcement of existing legislation protecting the species, and the development of a national recovery strategy. Research and monitoring programmes are also essential in order to devise and guide appropriate conservation efforts (2).

Mona Island is part of the Commonwealth of Puerto Rico, and is designated as a natural reserve by the Division of Natural Reserves and Refuges within the Puerto Rico Department of Natural Resources and the Environment (PR-DNRE). In conjunction with other organisations, the PR-DNRE has implemented some significant conservation measures, such as moving the hunting season to a time outside of the iguana’s nesting season, fencing off important habitat and remote nest sites from goats and pigs, and conducting research into the impact of feral cats and the blindness syndrome seen in several adult iguanas. Nevertheless, as the number of visitors to the island continues to grow, it is essential that they are better supervised, and that educational programmes raise awareness of the potentially damaging effects recreational activities can have to this endangered subspecies (2).

For more information on the rhinoceros and other iguana see:

Alberts, A. (1999) West Indian Iguanas: Status Survey and Conservation Action Plan. IUCN/SSC West Indian Iguana Specialist Group, Gland, Switzerland and Cambridge. Available at:
http://www.iucn-isg.org/actionplan/

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

  1. IUCN Red List (June, 2006)
    http://www.redlist.org
  2. Alberts, A. (1999) West Indian Iguanas: Status Survey and Conservation Action Plan. IUCN/SSC West Indian Iguana Specialist Group, Gland, Switzerland and Cambridge. Available at:
    http://www.iucn-isg.org/actionplan/
  3. CITES (June, 2006)
    http://www.cites.org
  4. Animal Diversity Web (June, 2006)
    http://animaldiversity.ummz.umich.edu/site/accounts/information/Cyclura_cornuta.html
  5. About: Animal Profiles (June, 2006)
    http://animals.about.com/od/reptiles/p/rhinocerosiguan.htm
  6. Nashville Zoo (June, 2006)
    http://www.nashvillezoo.org/riguana.htm