Stochastic variation in sex ratios in infant mortality rates due to small samples in provisioned Japanese macaque (Macaca fuscata) populations

Sex differences in infant mortality in provisioned Japanese macaque populations were examined using 10 data sets from five populations. The results indicate that there was no available data set in which a sex difference in infant mortality was statistically significant. To examine whether the observed sex ratios in infant mortality rates could be the product of stochastic variation in small samples, a correlation between sample size and the magnitude of sex ratios in infant mortality rates was also examined. Notably, the magnitude of sex ratios in infant mortality rates declined significantly as sample sizes increased. These results suggest that previously reported marked sex ratios in infant mortality could be the product of stochastic variation in small samples.