Validation of incubation duration as an index of the sex ratio of hatchling sea turtles

One method of estimating the sex ratio of hatchling sea turtles is to use t he incubation duration. Long and short durations imply low and high tempera tures, respectively. In turtle species whose sex is determined by temperatu re, males are produced at low temperatures and females at high temperatures . This study assesses the validity of using incubation duration to estimate the sex ratio. Samples of hatchling loggerhead turtles (Caretta caretta) w ere collected from nests with known incubation durations, and sex was ascer tained by means of histology. The sex ratio of groups of nests determined b y histology was compared with that predicted from previous relationships be tween incubation duration and sex ratio. For conditions causing relatively long or relatively short incubation durations, the sex ratio could be predi cted with considerable accuracy. For conditions causing durations nearer to the pivotal duration (that which gives 50% of each sex), predictions could be off by 10%, depending on the distribution of incubation durations, but it was still possible to determine whether ratios were highly skewed or app roximately balanced. Estimating sex ratios of hatchling sea turtles from in cubation durations is simple, cheap, and can be used retrospectively.