Saint Croix ground lizard (Ameiva polops)
|Also known as:||St. Croix ground lizard|
|Size||Length (excluding tail): 35 – 77 mm (2)|
Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1).
The Saint Croix ground lizard is a small lizard characterised by a distinctive pattern of longitudinal stripes down its back and rings around its tail, giving the species its highly unique appearance (3). A striking pattern of light brown, dark brown to black, and white stripes run down the length of the back (3). Below these are a series of narrow brown, black and white vertical stripes, which extend from the sides down to the stomach. The stomach is light grey with bright blue markings, which extend down the tail (3). A deep pinkish-red hue colours the underside of the legs, throat and chest (3). The long tail has alternating rings of blue and black, and blends from a browner tone near the body to a deeper blue colour at the tip (3).
Historically, this species was found on Saint Croix and its offshore islets and cays in the U.S. Virgin Islands (3). Today, populations are native only to Green Cay and Protestant Cay off the north coast and have been introduced to the manmade Ruth Cay off the south coast of Saint Croix, having not been seen on Saint Croix itself since 1968 (3).
Found in beach areas and upland forest, frequently amongst leaf litter and tidal litter, or in crab burrows (7). Smaller individuals are found in more exposed habitat while larger lizards are found in more canopied areas (8).
There have been no comprehensive studies of this lizard’s biology and very little is therefore known about its life history and behaviour (3).
The Saint Croix ground lizard is known to be a ‘heliothermic temperature regulator’, meaning that it is active during the warmest, middle portion of the day. During the night and on cooler, cloudy days the lizard tends to stay within its burrow under rocks or underground. An opportunistic hunter, this lizard actively prowls, roots and digs for virtually any prey items it can find, including amphipods (small, shrimp-like crustaceans), moths, ants, small hermit crabs, and the eggs and hatchlings of anoles (4).
The main reasons for the disappearance of the Saint Croix ground lizard on Saint Croix Island are habitat loss and the introduction of a mammalian predator, the Indian mongoose (Herpestes auropunctatus), both of which continue to threaten the future of the species in its remaining range (2). There is evidence that the decline on Saint Croix Island correlates with the introduction of the Indian mongoose in 1884 (2). The accidental introduction of the mongoose onto Green, Protestant or Ruth Cay could be catastrophic, most likely resulting in the extinction of the species (7).
Extensive development of coastal areas probably also contributed to the disappearance of this lizard on Saint Croix (2), and poses a significant threat to remaining populations. Suitable habitat is rapidly diminishing on Protestant Cay due to landscaping practices by hotel management, including activities such as raking, removal of leaf litter and undergrowth, and planting of exotic vegetation (8). A second concern is the vulnerability of the Saint Croix ground lizard to natural disasters such as hurricanes that strike the islands of both Green and Protestant Cay (2).
With such small, isolated populations, the Saint Croix ground lizard now faces the additional threat of reduced genetic variation through inbreeding, which would make it more vulnerable to natural disasters or disease as well as having a negative impact on fertility (7).
Green Cay was established as a National Wildlife Refuge in 1977 by the U.S. Fish and Wildlife Service to protect the largest remaining population of the Saint Croix ground lizard. This refuge protects 14 out of the 18 acres of designated critical habitat on Green Cay, which is closed to the public, keeping human disturbance to a minimum (7).
Recently, a cooperative agreement has been drawn up between the U.S. Fish and Wildlife Service and a private hotel (Hotel on the Cay) on Protestant Cay for the conservation and management of this endangered lizard. Efforts have included the recruitment of students from a range of middle and high schools to help restore and maintain the lizard’s habitat on the island (3).
Ruth Island was not created to protect this lizard, but ten individuals were translocated there in 1990 for this purpose. Recent population estimates suggest that the population has grown to become the second largest for this species, around 60 individuals, and such increases are extremely encouraging (4). With this success, the reintroduction of a recommended 50 lizards on to Buck Island has been planned, now that a mongoose eradication programme has been carried out on the island (3). This hardy species appears to be capable of thriving on mongoose-free islands if habitat remains relatively undisturbed (3). Thus its release on Buck Island will help reignite hope for the future survival of this tiny lizard.
For more information on the Saint Croix ground lizard see:
- U.S. Virgin Islands Department of Planning and Natural Resources, Division of Fish and Wildlife:
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IUCN Red List (December, 2009)