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Cyclura cornutaRhinoceros Iguana

By John Egnatios-Beene

Geographic Range

Cyclura cornuta is found only on the island of Hispaniola in the Caribbean Sea (Hamlett 2002). A closely related species or subspecies (scientific opinions vary) was found on Navassa Island, but is now believed extinct. There is a living subspecies on Mona Island, near Puerto Rico.

Habitat

The natural habitat of C. cornuta is typically described as dry forest, scrub, or desert. This biome receives very little rain annually and the plants and animals which occupy it reflect the sun-drenched, arid environment. Mostly small trees and shrubs, cacti, and mesquite may surround the burrows that C. cornuta inhabits. Iguanas exhibit a considerable amount of plasticity in their habitat selection and C. cornuta is no exception. This species is primarily found near coastlines, however, human expansion has forced many populations to retreat further inland. This species requires warm temperatures and lots of solar radiation. Cyclura cornuta is typically found in regions where the annual mean temperature is at least 27 degrees Celsius. It has been displaced from much of its original range on Hispaniola by habitat destruction and introduced predators (Hamlett 2002, Cyclura.com 2002)

Physical Description

The skin of C. cornuta has rough epidermal scales and is grayish brown or olive in color. The species is definitively identied by the large size of certain scales on the head, but few other iguana species are as large or have the "horns" (actually enlarged scales) on their heads. These horns are the source for the name for of the species. Males are larger than females and have relatively larger horns as well (Hamlett 2002, Cyclura.com 2002).

Development

These iguanas hatch from eggs and are independent after hatching. They mature at 5 to 9 years of age (Cyclura.com 2002).

Reproduction

Evidence for a polygynous mating system with social rank determining matings has been published. This corresponds to the fact that C. cornuta appears to be extremely territorial and males especially will attempt to dominate and intimidate conspecifics with head movements and body gyrations. They use similar motions to attract females, and may also use these head bobs and nods to scare away predators (Hunsaker II, et al. 1969).

The beginning of the mating season is late May, and C. cornuta is oviparous, so eggs are laid about 40 days after mating, usually in early August. Females dig burrows up to a meter and a half long in which to incubate the eggs and must keep them at a minimum of 30 degrees Celsius. Clutch size is extremely variable and may range from 5 to 20 eggs. Resource competition and/ or abundance of predators is thought to account for variations in egg-laying behavior(Hunsaker II, et al. 1969).

  • Breeding season
    late May to early June
  • Range number of offspring
    5 to 20
  • Average number of offspring
    10
  • Range gestation period
    4 to 5 months
  • Range age at sexual or reproductive maturity (female)
    5 to 9 years
  • Range age at sexual or reproductive maturity (male)
    5 to 9 years

There is no male parental care this species. Once females have laid their eggs, they sometimes guard the nest for a few weeks to prevent egg predation (D. Blair at Cyclura Research Information Collection).

Lifespan/Longevity

Very little has been published regarding the longevity of this species because it is difficult to monitor in the wild. A life of 20 years in captivity is reported (Hamlett 2002), and some researchers predict that these animals may live decades long than that in the wild (Kaplan 2002, citing Blair).

Behavior

Like all Iguanas, C. cornuta are behavioral heliotherms. This means that they must adjust their activity patterns to utilize solar radiation so as to regulate their body temperature. It also means that there are some obvious habitat restrictions for this animal--it can only survive in tropical or sub-tropical climates in the wild. When kept as a pet, it is often necessary to provide this species with an auxillary source of heat (such as a lamp) as many homes are kept below the appropriate temperature (Houston Zoo).

Most of the documented behavior unique to C. cornuta revolves around mating behavior. The aggressive displays that accompany mate guarding and territoriality have been discussed above (Hunsaker, et al. 1969)

Food Habits

Members of C. cornuta have a variable diet both seasonally and ontogenetically. Rhinoceros iguanas are mainly herbivores, eating a wide variety of leaves, fruits, flowers, and seeds. They occasionally eat animal food, mainly insects, land crabs, or carrion (especially dead birds and fish). Young iguanas in particular may take insects and other small animals. Iguanas that locate a food source (e.g. a fruiting bush) will actively defend it from conspecifics (Animal Network).

  • Animal Foods
  • carrion
  • insects
  • terrestrial non-insect arthropods
  • Plant Foods
  • leaves
  • seeds, grains, and nuts
  • fruit
  • flowers

Predation

The skin color of C. cornuta allows it to blend in with its environment. This species also exhibits behaviors which are thought to deter predators as well as competitors. As discussed above, these include elaborate head and neck movements intended to make the lizard look larger and more fierce. These defenses don't work very well against introduced predators.

Ecosystem Roles

Cyclura cornuta has been documented to feed on fruits. Because most seeds are difficult to digest without special bacteria, they often remain intact and end up in the animal's feces. This helps to both spread the seed and to fertilize it. C. cornuta therefore is crucial in communities in which it is the dominant frugivore.

  • Ecosystem Impact
  • disperses seeds

Economic Importance for Humans: Positive

Rhinoceros iguanas are sometimes kept as pets, and in the past have been used as food. Currently they are not of great economic importance.

Economic Importance for Humans: Negative

This species will bite or scratch and strike with its tail if provoked or attacked, but is otherwise harmless and in no way detrimental to humans.

Conservation Status

C. cornuta is threatened by human encroachment on and destruction of its natural habitat. The demand for old growth trees by the logging industry, limestone mining, pollution, predation, and wild fires have depleted the habitat and often forced this and many other species to migrate and/or go extinct. Haiti, a country mired in poverty, in particular has experienced a dramatic reduction in population due to poachers killing for food (Hamlett 2002). This species is listed as Vulnerable by the International Union for the Conservation of Nature, and is listed in Appendix I of CITES. This means that international trade in this species is generally forbidden with out strict permits from both exporting and importing countries. The closely related species/subspecies, C. cornuta stegneri, the Mona Island Ground Lizard, is considered Threatened by the U.S. Fish and Wildlife Department and protected under the Endangered Species Act.

Other Comments

There is legal trade in captive-bred rhinoceros iguanas. Potential purchasers should always insist on full documentation to ensure that they are not getting illegally collected wild animals. Illegal collection endangers the species, and is bad for the pet trade, as wild animals often carry parasites and diseases that have been eliminated from captive-bred populations.

Contributors

John Egnatios-Beene (author), University of Michigan-Ann Arbor, Kerry Yurewicz (editor), University of Michigan-Ann Arbor.

Glossary

Neotropical

living in the southern part of the New World. In other words, Central and South America.

World Map

carrion

flesh of dead animals.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

folivore

an animal that mainly eats leaves.

food

A substance that provides both nutrients and energy to a living thing.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

frugivore

an animal that mainly eats fruit

granivore

an animal that mainly eats seeds

herbivore

An animal that eats mainly plants or parts of plants.

internal fertilization

fertilization takes place within the female's body

island endemic

animals that live only on an island or set of islands.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

polygynous

having more than one female as a mate at one time

scrub forest

scrub forests develop in areas that experience dry seasons.

seasonal breeding

breeding is confined to a particular season

solitary

lives alone

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

threatened

The term is used in the 1994 IUCN Red List of Threatened Animals to refer collectively to species categorized as Endangered (E), Vulnerable (V), Rare (R), Indeterminate (I), or Insufficiently Known (K) and in the 1996 IUCN Red List of Threatened Animals to refer collectively to species categorized as Critically Endangered (CR), Endangered (EN), or Vulnerable (VU).

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

References

"Terrestrial Ecoregions- - Hispaniolan dry forests" (On-line). Accessed March 5, 2002 at http://www.nationalgeographic.com/wildworld/profiles/terrestrial/nt/nt0215.html.

Fink, W., A. Kluge. August, 2001. Chordates: Their Anatomy, Ontogeny, and Phylogeny. Ann Arbor, MI: University of Michigan.

Hamlett, L. "Rhinoceros Iguana" (On-line). Accessed 9 October 2002 at http://www.nashvillezoo.org/riguana.htm.

Hunsaker II, D., B. Burrage. April 1969. The significance of interspecific social dominance in Iguanid lizards. American Midland Naturalist, 81( 2): 500-511.

International Reptile Conservation Foundation, "Cyclura.com" (On-line). Accessed 9 October 2002 at http://www.cyclura.com.

Kaplan, M. "Cyclura Research Information Collection" (On-line). Accessed 9 October 2002 at http://php.indiana.edu/%7Eemartins/Melissa.

anonymous (Houston Zoo), "Rhinoceros Iguana" (On-line). Accessed March 3, 2002 at http://www.houstonzoo.org/reptiles/pages/rhinoigu.htm.

anonymous, "Species Profiles: Hispaniolan Rhinoceros Iguana" (On-line). Accessed March 1, 2002 at http://www.animalnetwork.com/reptiles/profiles/profileview.asp?RecordNo=359.

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