Redirected aggression reduces the cost for victims in semi-provisioned free-ranging Japanese macaques (Macaca fuscata fuscata)

Abstract

In many social species, the victim often attacks an uninvolved third individual soon after a conflict. This behaviour is called ‘redirected aggression’ or ‘redirection’, and its role(s) remain(s) controversial. We observed semi-provisioned free-ranging Japanese macaques at Iwatayama Monkey Park in Arashiyama, Kyoto, Japan, to test three hypotheses concerning the function of redirected aggression: Japanese macaques perform redirection to (1) indirectly retaliate against the aggressor, (2) reduce post-conflict stress, or (3) reduce post-conflict uncertainty. When we observed aggressive interactions, we recorded the behaviour of victims during the subsequent 10 min. Redirection occurred more frequently when the rank of the victim of the initial conflict was high, when the victim was an older monkey, and when conflicts occurred among kin. The results largely supported hypothesis 3. Victims received renewed aggression not only from the initial aggressor but also from bystanders more frequently within 1 min after the initial conflict than in the subsequent 9 min. Victims who performed redirection received less aggression from bystanders. Victims might have been able to avoid renewed aggression because they could change their state from victim to aggressor by performing redirection. This effect of redirection did not differ with the victim’s rank. However, the lower the victim’s rank, the higher the risk that they would receive retaliation from the target of the redirected aggression or the latter’s kin. Thus, redirection caused the same magnitude of benefit and a different magnitude of risk according to the victim’s rank. The victim may need to judge his/her own situation when making the decision as to whether to perform redirection.