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Distribution

    Distribution
    provided by Animal Diversity Web

    Grand Cayman rock iguanas, Cyclura nubila lewisi, are endemic to the Caribbean island of Grand Cayman. They were formerly widespread in dry and coastal habitats throughout the island, but due to severe habitat loss and predation, they are now found only in the High Rock-Battle Hill area to the east and south of the Queen’s Highway.

    Biogeographic Regions: neotropical (Native )

    Other Geographic Terms: island endemic

Morphology

    Morphology
    provided by Animal Diversity Web

    Grand Cayman rock iguanas are among the largest lizards in the Western Hemisphere, weighing over 11 kg and measuring over 1.5 m from head to tail. Males are typically larger than females. Snout-vent length can measure as long as 51.5 cm in males and 41.5 cm in females, and the tail is of equal length.

    Grand Cayman rock iguanas are characterized by even, stiff dorsal spines and a spineless dewlap. Their body is covered in scales, and some enlarged scales are present on the head region. Young iguanas have a gray base color with alternating dark gray and cream chevrons. As they mature, the juvenile pattern fades, and the hatchling base color is replaced by a blue-gray base complexion. Some dark chevrons are retained in adulthood. This blue-gray color is typical of ground iguanas when resting. However, ground iguanas are better known for the stunning shades of turquoise blue they take on during the mating season. For this reason, C. nubila lewisi is also known as the blue iguana.

    Range mass: >11 (high) kg.

    Range length: >1.5 (high) mm.

    Sexual Dimorphism: male larger

Habitat

    Habitat
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    Grand Cayman rock iguanas are ground dwelling and may occupy a number of habitats including forest, grassland, and coastal regions, as well as human-modified habitats. They mainly occur in natural xerophytic shrubland and along the interfaces between farm clearings and canopy dry forest. Farms provide a variety of resources such as vegetation, fallen fruit, and nesting soil.

    Grand Cayman rock iguanas spend their nights in retreats such as caves and crevices found within eroded rock, usually heavily eroded limestone. Although iguanas preferentially select natural rock substrate for retreat, they also utilize artificial retreats such as piles of construction material and spaces under buildings. Whereas adults are primarily terrestrial, younger individuals tend to be more arboreal. Occasionally, Grand Cayman ground iguanas may retreat in tree hollows or exposed on tree limbs.

    Habitat Regions: terrestrial

    Terrestrial Biomes: savanna or grassland ; forest

    Aquatic Biomes: coastal

Trophic Strategy

    Trophic Strategy
    provided by Animal Diversity Web

    Grand Cayman rock iguanas are primarily herbivorous, consuming mostly plant matter from at least 45 plant species in 24 different families. Leaves and stems are consumed most frequently, while fruits, nuts, and flowers are consumed in smaller quantities. Carnivory makes up a small percentage of the diet. This includes predation of invertebrates such as insects, slugs, and moth larvae. Grand Cayman rock iguanas have also been observed ingesting small rocks, soil, feces, bits of shedding, and fungi.

    Animal Foods: insects

    Plant Foods: leaves; wood, bark, or stems; seeds, grains, and nuts; fruit; flowers

    Other Foods: fungus; dung

    Primary Diet: herbivore (Folivore , Frugivore )

Associations

    Associations
    provided by Animal Diversity Web

    Grand Cayman rock iguanas are important seed dispersers of many native plants.

    Ecosystem Impact: disperses seeds

    Associations
    provided by Animal Diversity Web

    Young Grand Cayman rock iguanas are heavily preyed upon by a variety invasive species, including feral cats, mongooses, dogs, rats, and pigs. Predation by feral exotics is regarded as one of the major threats to the species and is greatly responsible for the critical population decline. Rats can cause severe injury to hatchlings and may cause mortality. The primary native predator of hatchlings is Alsophis cantherigerus. Adult Grand Cayman rock iguanas have no natural predators, but they are threatened by roaming dogs. Adults are also trapped and killed by humans. Ground iguanas may use head bobbing to scare away predators.

    Known Predators:

    • Alsophis cantherigerus

Behavior

    Behavior
    provided by Animal Diversity Web

    Grand Cayman rock iguanas use visual signals, such as head-bobbing, to communicate. They also communicate using pheromones, which are released from femoral pores located on the thighs of males.

    Communication Channels: visual ; chemical

    Other Communication Modes: pheromones

    Perception Channels: visual ; chemical

Life Cycle

    Life Cycle
    provided by Animal Diversity Web

    Grand Cayman rock iguanas lay their eggs in a nest chamber that is dug about a foot below the surface of the soil. While in the nest, eggs take up moisture from the earth. They gradually fill out until they are tight and under slight pressure. On average, Cyclura eggs are among the largest of all lizards. Eggs hatch in 65 to 100 days depending on temperature. The process of hatching may take longer than 12 hours. Hatchlings cut through the leathery egg shell using a microscopic “egg tooth” on the tip of their jaw.

    The combined effort of many hatchlings is required to dig out of the nest chambers. Occasionally Ground Cayman rock iguanas do not emerge from the next chamber for as long as two weeks after hatching. Throughout this period, hatchlings survive off of the remaining egg yolk stored inside their abdomen. They can live off of yolk remains for weeks before needing to feed or drink.

    Young iguanas are independent after hatching. They tend to be arboreal and spend most of their young life in trees in order to avoid terrestrial predators.

Life Expectancy

    Life Expectancy
    provided by Animal Diversity Web

    It is believed that Grand Cayman rock iguanas are among the longest lived species of lizard. In the wild, they are thought to reach ages of at least 25 to 40 years. However, rock iguanas can grow much older when kept in captivity. The longest living member of this species was a captive iguana known as “Godzilla” who survived to an estimated 69 years. It is doubtful, however, that wild iguanas can survive to this age, because Godzilla required extraordinary maintenance in the years before his death.

    Range lifespan
    Status: captivity:
    69 (high) years.

    Typical lifespan
    Status: wild:
    25 to 40 years.

Reproduction

    Reproduction
    provided by Animal Diversity Web

    Grand Cayman rock iguanas are solitary except during the mating season. Mating is generally polygamous, but some individuals may also be promiscuous or monogamous. During the breeding season, the home range of a dominant male frequently overlaps that of one or more females.

    Throughout the breeding season, Grand Cayman rock iguanas take on an intense blue coloration. In the spring, hormones surge and males begin to reassert dominance. Males lose weight during this time, as they devote their energy to breeding and dominating other males. Males expand their territory range, attempting to monopolize as many female territories as possible. Males in overlapping territories challenge each other, and, in most cases, smaller iguanas flee from larger individuals. Physical contact and fighting is rare and is usually restricted to individuals of similiar size. Fights can be vicious and bloody. Toes, tail tips, crest spines, and chunks of skin may be torn off in combat.

    By March, the abdomen of female Grand Cayman rock iguanas is swollen, as their eggs have formed inside them. They do not become receptive to breeding until late April. Females generally avoid males until they begin to mate in May, retreating into their rock holes whenever males are nearby. Gravid females reduce food intake about 2 weeks before oviposition, because their digestive tract is squeezed by the expanding mass of eggs. They also increase activity levels during this time.

    Copulation is preceded by a mating ritual. A male bobs its head then circles around behind a female. He grasps the nape of her neck and attempts to restrain her. The male maneuvers his tail under that of the female and positions himself for intromission. Copulation rarely lasts longer than 30 to 90 seconds, and a pair rarely mates more than once or twice per day. Mature pregnant females display a distended abdomen, and the outline of individual eggs may be seen.

    At the end of the receptive period, female Grand Cayman rock iguanas become intolerant of males and chase them out of their territories. Females become so aggressive, in fact, that a female can successfully scare off males much larger than herself.

    Mating System: polygynous

    The breeding season of Grand Cayman rock iguanas lasts 2 to 3 weeks between late May and mid June. Oviposition occurs approximately 40 days after fertilization, generally during the months of June and July. Females lay 1 to 22 eggs each year. Clutch size varies with age and size of females. Older, larger females are able to produce more eggs. Eggs are then incubated in the nest chamber that is dug about a foot below the surface of the soil. Incubation period ranges from 65 to 90 days. Temperature within the nest remains relatively constant at 30 to 33 degrees Celsius throughout this period. Grand Cayman rock iguanas usually begin breeding around 4 years of age in captivity. In the wild, they reach sexual maturity between 2 and 9 years of age.

    Breeding interval: Female Grand Cayman rock iguanas breed once yearly.

    Breeding season: Copulation occurs from late May until mid June. Egg-laying occurs approximately 40 days later in the months of June and July.

    Range number of offspring: 1 to 22.

    Average gestation period: 40 days.

    Average time to independence: 0 minutes.

    Range age at sexual or reproductive maturity (female): 2 to 9 years.

    Range age at sexual or reproductive maturity (male): 2 to 9 years.

    Key Reproductive Features: seasonal breeding ; sexual ; fertilization ; oviparous

    Female Grand Cayman rock iguanas often travel outside of their normal range to locate suitable nesting areas. Nest burrows are dug in sand or soil exposed to the sun. Several days before laying their eggs, females begin to dig in preparation for building their nests. It may take an entire afternoon to excavate a complete nest burrow. Female ground iguanas remain in nest burrows overnight to lay their eggs. While most emerge the following morning, some females remain underground for up to 2 days while laying their eggs. A female iguana fills the nest burrow with sand until a large mound is formed over the nesting site. She then scatters leaves over the area until the nest is completely disguised. When the nest is secure, she allows herself to feed again but remains close to the next. Females guard their next site for several weeks to prevent other iguanas from using the area for nesting and to protect from predators. Hatchlings are vulnerable to native snakes, such as Alsophis cantherigeruscaymanus, and suffer an extremely high mortality rate.

    There is no direct parental investment of Grand Cayman rock iguanas after hatching.

    Parental Investment: no parental involvement; female parental care ; pre-fertilization (Protecting: Female); pre-hatching/birth (Protecting: Female)

Conservation Status

    Conservation Status
    provided by Animal Diversity Web

    Cyclura nubila lewisi is one of the fastest disappearing and most critically endangered species on Earth. The decline of Grand Cayman rock iguanas likely began in pre-Colombian times when they were hunted for food by native Indians of the Arawak and Lucayan tribes. More severe decline began with European settlement of the Cayman Islands. As the human population increased, extensive habitat was cleared for agriculture as well as residential and commercial developments. Today, habitat loss is the main factor threatening extinction of Grand Cayman rock iguanas. Construction of vehicular roads resulted in further habitat destruction and has brought fast-moving traffic into remnant habitats. This occasionally results in vehicular deaths.

    Another major threat associated with European settlement was the introduction of invasive species to the island, such as cattle, goats, pigs, rats, cats and dogs. Grand Cayman rock iguanas face predation by or competition with these introduced animals. Less frequently, iguanas may be illegally trapped or shot at by farmers who perceive iguanas as a threat to their crops.

    The National Trust for the Cayman Islands established The Blue Iguana Recovery Programme in 1990. This conservation program incorporates research, habitat protection, captive breeding, reintroduction, and conservation education. Despite protection of 2000 acres of dry forests and mangrove wetlands within the Cayman Islands, suitable protected land for Grand Cayman rock iguanas is very scarce.

    The Blue Iguana Recovery Programme has been successfully breeding C. nubila lewisi in captivity since 1990. Members of this species are reared until they are 2 years old and released into the Queen Elizabeth II Botanic Park on Grand Cayman. These young iguanas help to supplement existing wild populations and also to establish new wild populations in protected areas.

    Grand Cayman rock iguanas are fully protected under local legislation and are considered critically endangered by the IUCN. It is illegal to kill, capture, or hold members of this species in captivity. Furthermore, international trade of this species is prohibited, as it is listed on Appendix I of the Convention on International Trade in Endangered Species (CITES).

    US Federal List: endangered

    CITES: appendix i

    IUCN Red List of Threatened Species: critically endangered

Benefits

    Benefits
    provided by Animal Diversity Web

    Grand Cayman rock iguanas may feed on and disrupt agricultural crops.

    Negative Impacts: crop pest

    Benefits
    provided by Animal Diversity Web

    Grand Cayman rock iguanas once served as a food item to the native people of the Grand Cayman. Currently, this species is a major attraction for ecotourists. Rock iguanas are occasionally illegally captured, sold, and kept as pets.

    Positive Impacts: pet trade ; food ; ecotourism