Sex ratio adjustment by sex-specific maternal cannibalism in hamsters

► Syrian hamster dams routinely cannibalize a substantial number of their pups. ► We assessed the impact of day length on pup cannibalism and sex ratios. ► Short day lengths induced significantly male-biased sex ratios at weaning. ► Hamster dams in both long and short day lengths predominantly cannibalized female pups. ► Large initial litter size was associated with more cannibalism, smaller final litters, and heavier pups.