The Rock Iguana, Cyclura pinguis, on Anegada, British Virgin Islands, with Notes on Cyclura ricordi and Cyclura cornuta on Hispaniola

Abstract

A field study of the ethoecology of the rock iguana, Cyclura pinguis, on Anegada, British Virgin Islands was conducted from 27 March to 5 May 1968. The sympatric Hispaniolan species, C. ricordi and C. cornuta, were observed from 12 to 16 May 1968. The results of these studies and all known ethoecological literature on the genus are discussed. Cyclura pinguis inhabits primarily xeric limestone areas, is heliothermic, and exhibits behavioral thermoregulation. Retreats nearly always consist of natural cavities in the limestone or beneath boulders. C. ricordi and C. cornuta are primarily burrowers. Adult of all three species are principally herbivorous, although some animal matter is taken. Probably all Cyclura juveniles are primarily insectivorous. Parasitism from ticks and nematodes is a common occurrence in Cyclura. Five adult males on the main study plot ranged from 522 to 545 mm (x̅ = 534.60 ± 3.88 mm) in snout-vent length and from 5.95 to 7.17 kg (x̅=6.72 ± 0.21 kg) in body weight; five adult females ranged from 426 to 487 mm (x̅ = 468.00 ± 10.87 mm) in snout- vent length and from 4.31 to 5.13 kg (x̅ = 4.75 ± 0.13 kg) in body weight. The five males occupied home ranges from 116.06 to 985.11 m2 (x̅ = 546.61 ± 160.46 m2) in area; home ranges of the five females measured from 155.47 to 412.31 m2 (x̅ = 276.28 ± 41.62 m2). Extensive unutilized zones existed between home ranges of iguanas of the same sex. Aside from food, available shelter seems to be the most importait factor governing selection of home range locale. Cyclura pinguis exhibited a density of 2.03 iguanas/hectare (0.82/acre), the lowest density figure of any lizard for which data are documented. The sex ratio was equal. Evidence suggests monogamy. Three adult females had 12, 14, and 16 yolked ovarian follicles. Adulthood appears to be attained between 7 and 9 years of age and between 350 and 400 mm snout-vent length. The reproductive cycle in C. pinguis suggests synchronization with the two rainfall maxima in the Virgin Islands. Adult iguanas far outnumbered juveniles (87.5% vs. 12.5%) suggesting decline of the population. This disproportionate age structure seems to be the result of interactions (competition/predation) with domestic livestock. With the resultant loss in fecundity, relatively few adults now exist to continue the population. A conservation program is outlined whereby the population might be restored. This program might be applicable to other decimated Cyclura populations as well.