Female social behaviour during three male introductions in captive groups of rhesus macaques

Introductions of new males into captive primate groups are often necessary to prevent inbreeding, but also bear high social risks. To minimize these risks, it is crucial to understand the social behaviour accompanying male introductions. While the behaviour of new males is generally understood, information on resident female behaviour during introductions is lacking. We studied female behaviour towards the new male during introductions of three adult male rhesus macaques (Macaca mulatta)-each into a different captive group. All three males were successfully introduced; respectively 100%, 92%, and 83% of the females tolerated the male as a group-member at the end of the introductions. Older females started tolerating the male significantly faster than younger females, while no additional effect of female dominance rank, fertility, or the number of female coalitionary partners on timing of tolerance was found. During the course of the integration, female aggression and submission towards the male, and male mating access decreased, while female affiliation towards the male increased. The increase of female tolerance and the changes in social behaviour were similar between the introductions, indicating a general pattern in female behaviour, although some variation in effect size and significance level was observed. Based on these results, we suggest that low female submission levels towards an introduced male may constitute a criterion to assess the risk of leaving the male in the group full-time. Moreover, low female aggression levels at the end of the introduction may signal long-term group stability. Overall, we conclude that female behaviour can provide valuable information about the male introduction process and should not be overlooked.