Overview

Brief Summary

Biology

The release of livestock on Anegada in 1968 has not only caused a decline in population numbers, but has also had a profound affect on the Anegada ground iguana's social organisation and diet (2). Estimates in the late 1960s showed the average home range size for iguanas on Anegada to be small, at less than 0.1 hectares, and non-overlapping (2) (4). Additionally, there were roughly equal numbers of males and females, each individual was found to occupy one principle burrow, and habits indicated monogamy, with pairs inhabiting separate but proximate burrows in a joint home range isolated from other pairs. However, by 1991, the sex ratio had changed to two males to every female. Now, home ranges are quite large and overlap, at 6.6 hectares for males and 4.2 hectares for females; with these changes thought to be a result of male competition for far more limited females (4). Males suspected of having a mate have noticeably smaller home ranges, presumed to be due to their greater need to guard the female against wandering bachelors. Females typically lay one clutch of around 12 to 16 eggs per year between May and June, and clutches hatch in August and September at the beginning of the rainy season, when there is greater availability of lush vegetation (2). Although predominantly herbivorous, the Anegada ground iguana is also an opportunistic carnivore, feeding on invertebrates such as beetles, caterpillars, centipedes and roaches supplementing a diet of leaves and fruit (4). Where the iguana's range overlaps with feral livestock, the bulk of the diet consists of plants that are rejected by the livestock. These are usually plants containing high levels of secondary compounds that are poorly digested and therefore of poor nutritional value (2).
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Description

The Anagada ground iguana was once distributed over the entire Puerto Rico Bank but, as its common name implies, its natural range is now restricted to the island of Anegada in the British Virgin Islands (4). This relatively large, stout species of Cyclura has a dusty-brown coloured back and a buff-white to pale grey belly. By contrast, the legs, sides, tail base and dorsal spines are strikingly coloured with varying amounts of brilliant turquoise blue, particularly pronounced in males (2) (4). Juveniles have a grey to moss-green back and sides and are distinctively patterned with a series of wide grey to black forward-pointing chevrons, which fade and are generally lost as the individual matures (2) (4). Eyes are normally a dull yellow, but flush bright crimson when the iguana becomes agitated (2) (4).
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Distribution

Range Description

The common name of the Anegada Island Iguana is misleading, as the animal was once distributed over the entire Puerto Rico Bank. Fossils are known from Saint Thomas and Puerto Rico. Vulnerability to predation by humans and their dogs and cats may have resulted in a contraction of its distribution to Anegada.
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Continent: Caribbean
Distribution: British Virgin Islands (Anegada Island), Puerto Rico Bank  
Type locality: Anegada Island, British Virgin Islands.
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Historic Range:
West Indies_British Virgin Islands (Anegada Island)

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Range

The natural range of the Anegada ground iguana has greatly reduced and is now confined to the island of Anegada in the British Virgin Islands (2). In addition two small introduced populations exist on Guana Island and Necker Island. The total population across all three islands is thought to number fewer than 200 individuals (1).
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Ecology

Habitat

Habitat and Ecology

Habitat and Ecology
Estimates in the late 1960s (Carey 1975) showed small home ranges for both sexes (less than 0.1 ha), one principal burrow per animal, a 1:1 sex ratio, and habits that indicated monogamy (apparent pairs inhabited separate but proximate burrows in a joint home range isolated from other pairs). The current population structure is quite different. While previous studies may not have been sensitive to long range movements, it now appears that home ranges are quite large on Anegada: males average 6.6 ha and females average 4.2 ha. Home ranges broadly overlap and have one or two centers of activity. In 1991 the sex ratio had dropped to 1 female:2 males. Thus male competition for limited females may be responsible for the high degree of home range overlap.

Burrows of both sexes may be located on the old limestone reef-tract or in sandy areas adjacent to it. If available, iguanas will use additional holes or crevices as emergency retreats. Whereas degraded vegetation may provide for male subsistence, it may not provide females with sufficient energy to allow them both to produce eggs and compete with other animals for forage to support their own growth and metabolism. Reproducing females may have low survivorship, resulting in the present skewed sex ratio. Females usually lay one clutch of about 12-16 eggs per year in late spring or early summer.

Although largely facultative herbivores, all age-groups of these iguanas are opportunistic carnivores. Invertebrates (beetles, caterpillars, centipedes, roaches) form less than 1% of the natural diet, although this may be a result of limited availability. The bulk of the diet consists of leaves and fruits.

Over the past 20 years, grazing pressure by goats, sheep, burros, and cattle has radically changed the vegetation composition of Anegada. The iguanas' diet is now composed of plant species the feral animals reject.

Systems
  • Terrestrial
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The Anegada ground iguana is closely tied to porous limestone habitats on Anegada, with burrows of both sexes being located on old limestone reef-tract or in sandy areas next to it (4). By contrast, both Guana and Necker are largely volcanic in origin and have few naturally occurring shelter sites, so fewer burrows are used and animals are more arboreal (2).
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Conservation

Conservation Status

IUCN Red List Assessment


Red List Category
CR
Critically Endangered

Red List Criteria
A1abcde, B1+2abce, C1+2b

Version
2.3

Year Assessed
1996
  • Needs updating

Assessor/s
Mitchell, N.

Reviewer/s

Contributor/s

History
  • 1994
    Endangered
    (Groombridge 1994)
  • 1990
    Endangered
    (IUCN 1990)
  • 1988
    Endangered
    (IUCN Conservation Monitoring Centre 1988)
  • 1986
    Endangered
    (IUCN Conservation Monitoring Centre 1986)
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Current Listing Status Summary

Status: Endangered
Date Listed: 06/02/1970
Lead Region: Foreign (Region 10) 
Where Listed: Entire


Population detail:

Population location: Entire
Listing status: E

For most current information and documents related to the conservation status and management of Cyclura pinguis , see its USFWS Species Profile

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Status

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1) and listed on Appendix I of CITES (3).
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Population

Population
Population density in 1968 was estimated at 2.03/ha (Carey 1975). In 1991, this figure had dropped to 0.36/ha in comparable habitat. Extrapolation of density estimates, distribution, and relative habitat quality yields a population estimate for Anegada of 164 individuals. A small restored population also exists on Guana Island with eight founding adults (Goodyear and Lazell 1994), from which three juveniles have been translocated to Necker Island. The total population, including individuals on Anegada, Guana, and Necker probably consists of fewer than 200 individuals.
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Threats

Major Threats
Areas on Anegada that once contained dense populations of iguanas now support few or none. Research indicates that this is due to three major causes, including competitive grazing pressure from free-ranging livestock, predation by feral dogs, and predation of juveniles by feral cats.
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Anegada ground iguana populations have undergone a drastic decline in recent decades, leaving possibly fewer than 200 total individuals teetering on the brink of extinction (5). The drop in numbers is probably attributable to a range of threats, including habitat loss and poaching by hunters who are trafficking exotic animals (2). Most devastating, however, has been the introduction of alien species (5). Feral dogs, first reported in 1994, are known to kill adult iguanas, and predation by an exploding population of feral cats on juveniles is responsible for the deaths of many hatchlings each year (2) (5). The primary threat, however, comes from competition for food from feral livestock, with the island teeming with sheep, goats, donkeys and cattle that have been released to roam freely across Anegada (2) (4). Grazing pressure from these livestock has radically changed the composition of vegetation available to the iguana, shifting the species' diet to rely more on plants with secondary compounds with dubious nutritional value (2).
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Management

Conservation Actions

Conservation Actions
A major grant has been received from the Environment, Science and Energy Department of the UK Foreign Commonwealth Office to facilitate conservation activities on Anegada. Goals of this program are to 1) implement a cat eradication/control feasibility study, 2) expand the current headstart facility, 3) train the Senior Terrestrial Warden in iguana husbandry and facility maintenance, 4) conduct population censusing and mapping at sites nesting sites and other potential sites where adults may be found, and 5) develop environmental education materials to raise public awareness of the importance and vulnerability of iguanas on Anegada.

In the 1980s, eight iguanas were moved from Anegada to Guana Island, British Virgin Islands, to start a second population in part of the species’ former range (Goodyear and Lazell 1994). This is not a limestone island, and does not provide as many natural retreats as Anegada. In the absence of introduced predators, however, the iguanas appear to do well and reproduce in areas that are free of sheep (the only feral grazing competitor present). Currently, approximately 20 adult iguanas are estimated to inhabit Guana. Offspring have been seen each year since 1987, but recruitment is very low over much of the island. Guana Island Wildlife Sanctuary continues to try to rid the island of sheep, which may improve the habitat for iguanas.

This species is listed on CITES Appendix I.
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Conservation

The Anegada Iguana Recovery Programme began in 1997, which included establishing a 'headstart' facility. This facility collects hatchlings and nurtures them in captivity until they can be safely released into the wild, with the aim of combating the high rates of juvenile mortality due to cat predation by raising them until they are large enough that predation will not pose as great a threat (6). The first 24 were released into the wild in October 2003, with an 84 percent survival rate, and a second group of 24 were released in October 2004, and these are currently being tracked (5). In the 1980s, small numbers of these iguanas were removed from Anegada and restored to parts of their former range, on Guana Island, where the species appears to be doing well in the absence of introduced predators (1) (2). The Guana Island Wildlife Sanctuary continues to try to rid the island of sheep, the only feral grazing competitor on the island, which may improve the habitat there for the iguanas (1). The species was also later introduced to Necker Island (2). A national park designed to protect this Critically Endangered iguana on Anegada has been approved in principle by the Anegada Lands Committee, but rampant debates over land ownership and property boundaries impede developments, and must be resolved before this project can progress (2) (4). Further conservation actions advocated include a cat eradication programme and the construction of fences around protected areas to keep livestock out. Indeed, despite the successes of the headstart programme, it is imperative that efforts are made to control livestock and to secure protected land for the survival of this species. Without prompt action, it has been suggested that these iguanas may become extinct on Anegada within the next decade (2).
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Wikipedia

Cyclura pinguis

The Anegada ground iguana[1] or stout iguana (Cyclura pinguis) is a critically endangered species of lizard of the genus Cyclura belonging to the family Iguanidae. The species can be found exclusively in the island of Anegada. Historically, it inhabited the islands of Puerto Rico and Saint Thomas, however, the animal's original range has been greatly diminished.[2]

Natural history[edit]

The Anegada ground iguana is noted as the oldest species of Cyclura and the most genetically divergent of the West Indies' rock iguanas.[3][4] An ancestor to this iguana first dispersed to Hispaniola, then onwards to the north and western islands, which has since diversified on different islands into the 9 species and several additional subspecies of the genus Cyclura as we know it today.[5]

Taxonomy[edit]

The Anegada ground iguana was first described by American Herpetologist Thomas Barbour 1917.[6][7] Its generic name (Cyclura) is derived from the Ancient Greek cyclos (κύκλος) meaning "circular" and ourá (οὐρά) meaning "tail", after the thick-ringed tail characteristic of all Cyclura iguanas, with the exception of the Anegada ground iguana.[8] Its specific name pinguis means "fat" and refers to the animal's stocky appearance and the common name "Stout iguana".[7]

Anatomy and morphology[edit]

The Anegada ground iguana is a large heavy-bodied rock iguana which attains a total body length of close to 22 inches(560 mm).[2] As juveniles they are faintly or boldly patterned with wide gray to moss green bands interspersed with wide gray to black anteriorly directed chevrons. These bands fade and are generally lost as the animals mature, turning a uniform grayish or brownish-black with varying amounts of turquoise on the dorsal spines, tail base, fore and hind legs. Occasionally this bluish coloration extends up onto the sides of the individual, particularly in males. Females tend to be relatively dull in color, exhibiting less brilliant blue if any.

This species, like other species of Cyclura, is sexually dimorphic; males are larger than females, and have more prominent dorsal crests, "horns" and femoral pores on their thighs, which are used to release pheromones.[9][10]

Diet[edit]

Like all Cyclura species the Anegada ground iguana is primarily herbivorous, consuming leaves, flowers and fruits from different plant species.[2] However, due to direct competition with grazing livestock in its native habitat such as sheep, goats, burros, and cattle they have been reduced to eating vegetation rejected by these domestic and feral animals.[2][3] This has also caused them to become opportunistic carnivores preying upon centipedes, millipedes, roaches, insects, and other invertebrates as opposed to being strict herbivores.[2]

Mating and habitat[edit]

This forced diet has had an impact on the iguanas' ability to reproduce.[2] As reproductive females are not being provided with enough nutrition to produce eggs and support their own metabolism; many do not survive after laying eggs, resulting in the present skewed sex ratio of 2 males to every female.[2] Females usually lay one clutch of about 12-16 eggs per year in late spring or early summer.[2][3]

Anegada Island is rare in that it is not a volcanic island, but formed from coral and limestone providing many caves and natural burrows for the iguanas to live.[2] Animals typically inhabit a single burrow and it was once observed that they appeared to bond for life, dwelling in burrows in close proximity to their mate.[2] As the drive to find more females and compete for food has increased their range, this does not appear to be occurring any longer.[2]

Conservation[edit]

Endangered status[edit]

It is estimated that the current global population is less than 300 and is rapidly declining: the population has decreased by at least 80% over the last 40 years.[2][3][11][12]

Causes of decline[edit]

In the brush

The primary reason for the Anegeda ground iguana's decline is competitive grazing with domestic and feral livestock.[2][3] The secondary reason is that they are preyed upon by feral dogs and cats.[2][3][11] As with other Rock Iguanas, their habitat is also in rapid decline due to development and logging.[2]

Live Anegada iguanas used to regularly be sold to tourists as pets, as their rarity made them more appealing to exotic animal collectors, despite this being illegal under the CITES treaty.[13] In 1999 a World Wildlife Fund international conservation officer, Stuart Chapman, said: "The British government has turned a blind eye for over 20 years to these overseas territories which are home to many rare and endangered species. Many of these face extinction if Britain fails to honour its treaty obligations. The British Caribbean islands are extremely rich in biodiversity with many critically endangered species that are unique to the islands - yet there is virtually zero enforcement or implementation of CITES." [13]

Recovery efforts[edit]

Intense conservation efforts are underway to protect this species.[4] In the 1980s, eight iguanas were moved from Anegada to Guana Island, British Virgin Islands, to start a second population in part of the species' former range.[2][14] Guana Island is not a limestone island, and does not provide as many natural retreats as Anegada does. The iguanas appear to be doing well and reproducing in areas free of feral sheep, which is its only competitor for vegetation. Approximately 20 adult iguanas are estimated to inhabit Guana and offspring have been seen each year since 1987.[2] Guana Island Wildlife Sanctuary continues to try to rid the island of sheep, which may improve the habitat for iguanas.[2]

The Anegada ground iguana has also been successfully bred in captivity at the San Diego Zoo and the Fort Worth Zoo.[11] Both zoos have actively been working with the British Virgin Islands on a joint-recovery program started in 1997 on Anegeda Island.[11] 120 iguanas have been raised at the facility for release into the wild.[11] Hatchlings are fed and protected so they can be "headstarted" for the wild and not fall prey to feral dogs and cats.[11] This offsets the juvenile mortality rate and is accompanied by field research, nestsite protection, and monitoring of released animals.[11][15]

References[edit]

  1. ^ Cyclura pinguis, The Reptile Database
  2. ^ a b c d e f g h i j k l m n o p q r Mitchell, N. (1996). Cyclura pinguis. 2006. IUCN Red List of Threatened Species. IUCN 2006. www.iucnredlist.org. Retrieved on September 8, 2007.
  3. ^ a b c d e f "Anegada Iguana". International Iguana Foundation - Anegada Iguana. International Iguana Foundation. October 21, 2006. Retrieved 9/8/2007. 
  4. ^ a b Malone, Catherine; Davis, Scott (2004), "Genetic Contributions to Caribbean Iguana Conservation", Iguanas: Biology and Conservation (University of California Press): 52–57, ISBN 978-0-520-23854-1 
  5. ^ "Blue Iguana's Relatives". Blue Iguana Recovery Project. Retrieved 9/10/2007. 
  6. ^ "Cyclura pinguis Barbour, 1917", Integrated Taxonomic Information System, 2001, retrieved 10/8/2007 
  7. ^ a b Hollingsworth, Bradford D. (2004), The Evolution of Iguanas: An Overview of Relationships and a Checklist of Species work = Iguanas: Biology and Conservation, University of California Press, p. 38, ISBN 978-0-520-23854-1 
  8. ^ Sanchez, Alejandro. "Family Iguanidae: Iguanas and Their Kin". Father Sanchez's Web Site of West Indian Natural History Diapsids I: Introduction; Lizards. Kingsnake.com. Retrieved November 26, 2007. 
  9. ^ De Vosjoli, Phillipe; David Blair (1992), The Green Iguana Manual, Escondido, California: Advanced Vivarium Systems, ISBN 1-882770-18-8 
  10. ^ Martins, Emilia P.; Lacy, Kathryn (2004), "Behavior and Ecology of Rock Iguanas,I: Evidence for an Appeasement Display", Iguanas: Biology and Conservation (University of California Press): 98–108, ISBN 978-0-520-23854-1 
  11. ^ a b c d e f g Hudson, Rick (2005), "Anegada Iguanas Released", Iguana Specialist Group Newsletter (International Iguana Foundation) 8 (1): 2–4, retrieved 9/8/2007 
  12. ^ Cogger, Harold; Zweifel, Richard (1992), Reptiles & Amphibians, Sydney, Australia: Weldon Owen, p. 126, ISBN 0-8317-2786-1 
  13. ^ a b Tickell, Oliver (1999-10-14), "UK `allowing illicit trade in endangered species'", The (London) Independent 
  14. ^ Iverson, John; Smith, Geoffrey; Pieper, Lynne (2004), "Factors Affecting Long-Term Growth of the Allen Cays Rock Iguana in the Bahamas", Iguanas: Biology and Conservation (University of California Press): 200, ISBN 978-0-520-23854-1 
  15. ^ Alberts, Allison; Lemm, Jeffrey; Grant, Tandora; Jackintell, Lori (2004), "Testing the Utility of Headstarting as a Conservation Strategy for West Indian Iguanas", Iguanas: Biology and Conservation (University of California Press): 210, ISBN 978-0-520-23854-1 
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