Estimating the sex ratio of loggerhead turtle hatchlings at Mon Repos rookery (Australia) from nest temperatures

Sand temperatures and loggerhead turtle nest temperatures (Caretta caretta) at Mon Repos rookery (Australia) were monitored over the 2005–06 and 2006–07 nesting seasons and hatchling sex ratios of clutches were estimated using the Constant Temperature Equivalent method. Nest temperatures were positively correlated with the sand temperature and air temperature in both seasons. Both seasons produced a female-biased sex ratio, especially the 2005–06 season, when almost all hatchlings were predicted to be female. Hatch success rate was not affected by nest temperature and averaged 85%, but hot nests from 2005–06 had a reduced emergence success compared with other nests. Daily cyclic temperature fluctuations of 0.5–1.5°C were a feature of nests, with a tendency for greater daily amplitude in the 2005–06 season when the average daily temperature was hotter. These daily temperature fluctuations increased the constant temperature equivalent temperature by 0.1–0.5°C above mean nest temperature during the sex-determining period and resulted in an increased female bias in the estimated hatchling sex ratio.