We studied the relationship between fluctuating temperatures in the field and sex ratios of the giant river turtle (Podocnemis expansa) obtained from nests incubated in seminatural conditions using a stepwise logistic regression model. The number of hours above 31 C and mean temperature above 31 C during day 29-30 were the two parameters that best explained sex ratios. We also monitored incubation temperatures of natural nests. Mean incubation temperature and the combination of mean and variance were not predictors of
