Nest-Site Selection and Offspring Sex Ratio in Painted Turtles, Chrysemys picta

Abstract

We studied the influence of nest-site selection on nest temperature and clutch sex ratio in a northern population of painted turtles (Chrysemys picta). Comparison of characteristics of pairs of nests of individual females, within and between years, provided no evidence that these females followed a simple pattern in choosing nest sites and no indication that they influenced sex ratio by choosing sites with specific characteristics. Microhabitat features of nests were compared to the same characteristics of randomly chosen sites in the nesting area and in contrast to randomly chosen sites, nests were significantly warmer and more likely to occur on slopes. Sex ratios produced in nests were not correlated with any measured nest characteristic except temperature, and nest temperatures were more dependent on yearly variations in climate than on variations in site characteristics. Nest-temperature distributions were unimodal, suggesting that fe- males selected nest sites to maximize the probability that eggs would complete development, rather than to influence offspring sex ratio.