Age and sex differences in behavioural responses of Japanese macaques (Macaca fuscata) towards snakes

Avoiding snake predation is essential for the survival of various animal species in the wild. Primates are occasionally predated by snakes, and their anti-predator strategies towards snakes can be better understood by field experiments that investigate behavioural responses to snakes. This study examined such behavioural responses of free-ranging Japanese macaques (Macaca fuscata) on Shodoshima Island. Three snake models (colored black, green, and yellow mottled) were presented to the subjects. Fleeing, alarm calls, looking, and latency of first response were recorded as behavioural responses. We analysed the effects of age and sex of the subject, as well as the effect of snake model on the frequency of each behaviour. Behavioural data were collected from 50 trials. Although the frequency of fleeing was higher in adult females than in adult males, such sex differences were not marked in juveniles. These results might be caused by sex role differences in primates, wherein males often display anti-predator behaviours for the protection of females and/or their offspring, whereas females prioritise protecting themselves and their offspring. Juveniles looked longer at the snake model than adults did, suggesting that juveniles acquire predator knowledge via observation. Age and sex differences were not observed in the frequency of alarm calls and latency of first response. None of the four behaviour measures was influenced by the snake model. This study highlights the age and sex differences in behavioural responses to snakes in non-human primates, contributing to a better understanding of anti-snake strategies in mammals and complex primate-snake relationships.