The relation between natural nest temperatures and hatchling sex ratios of American alligator (Alligator mississippiensis) has not been determined adequately. The few studies to date have been limited by study design, low sample size, and inadequate equipment. We investigated this relationship in 20 nests in impoundment habitat in South Carolina during 1995. Actual sex ratios were highly correlated (r = 0.971, P < 0.001) with sex ratios predicted from laboratory results, on the basis of mean nest temperatures between days 30-45 of incubation (temperature-sensitive period (TSP)). Mean nest temperatures during the TSP ranged between 29.1 to 33.8 C, with daily fluctuations within a nest ranging from 0.4 to 1.9 C. Rainfall appeared to have the greatest effect on nest temperatures. While nest temperatures provided a useful estimate of hatchling sex ratios, we recommend that researchers monitor hatchling sex ratios directly. Nest temperatures provide other relevant indicators for alligator management.
