Behavior and ecology of the rock iguana Cyclura carinata

Abstract

The natural history and social behavior of the rock iguana, Cyclum carinata, were studied during 25 weeks between September 1973 and June 1976 on several small cays in the Turks and Caicos Islands, British West Indies, and in captive enclosures in Gainesville, Florida. Reproductive cycles were synchronized to climatic cycles: Testes sizes were maximal in April and May (the end of the dry season). Vitellogenesis began in January (onset of the dry season); ovulation and mating occurred in early May. Courtship was typical of most iguanid lizards; the mating system was probably one of serial polygyny with monogamy among some males. A single annual clutch of 2 to 9 eggs was laid in early June in the terminal portion of the female's retreat burrow. Clutch size was positively correlated with female size. Clutch weight averaged about 25% of preoviposition weight. Females defended their nest burrows for several days to several weeks after nesting, but were not territorial during the remainder of the year. Hatching occurred after approximately 90 days. Neonates averaged 79.8 mm SVL and 14.6 gm. Juvenile growth rate averaged 19.2 mm SVL/year. Males reached sexual maturity at approximately 220 mm SVL and 375-475 gm and at an age of about 7 yr; females 185-200 mm, 200-300 gm at 6 to 7 yr. Adult males averaged 276 mm SVL and 935 gm, adult females 225 mm and 475 gm. The largest male measured 360 mm SVL and 1864 gm, largest female 292 mm and 1135 gm. Adults grew between 2 and 17 mm SVL/year. Rock iguanas were primarily herbivorous at all ages and fed arboreally and terrestrially. Five partial septa partition the proximal colon region; this modification presumably increases digestive efficiency. Huge oxyurid nematode populations inhabited the colon, and their relationship with the iguana may be mutualistic rather than parasitic. Abdominal fat deposits were negatively correlated with gonadal activity. Home range size was correlated with body size and habitat productivity, averaging 980 m2 for females, 1260 m2 for subdominant males, and 1590 m2 for dominant males. Diurnal activity was bimodal during warmer months; high midday temperatures resulted in reduced activity. Winter activity was generally reduced and peaked at midday. Iguanas basked following emergence; most of the remainder of the day was spent feeding, interacting with other lizards, and shuttling in the sun-shade mosaic for thermoregulatory purposes. Basking preceded the termination of daily activity. Rock iguanas performed ritualized "signature" displays or headbobs. Postural adjustments were among the modifiers producing variation in this display in different behavioral contexts. Displays were important to territory declaration, male challenging, and sex recognition. Males were territorial year-round in the field, but developed dominance hierarchies in captivity. Dominant males displayed less than subordinates. Male territorial defense probably evolved as a mechanism guaranteeing access to food resources and females for breeding. The sex ratio was 1:1 in all age classes. Survivorship was positively correlated with body size. Juvenile densities reached 90.3/ha in optimum habitat, adults exceeded 31.1/ha. Biomass estimates were 5.15 kg/ha for juveniles and 17.01 kg/ha for adults. Life table data indicate replacement rate was near unity, and mean generation time was 14.0 years. In its life history strategy, C. carinata is a predominately K-selected species.