Social bonds with males lower the costs of competition for wild female Assamese macaques

In polygynandrous mammals, females rarely form affiliative relationships with unrelated males outside the mating context. The antiharassment hypothesis provides one explanation for why such relationships have evolved in some gregarious primates: it states that females receive less aggression from group members in the presence of a male partner and gain his support when being harassed by others. This lowers the costs of competition and increases the female's access to resources, as it also reduces interruptions to feeding. Our aim was to test this hypothesis by investigating the benefits that wild female Assamese macaques, Macaca assamensis, in Thailand derive from bonding with particular males. In support of the antiharassment hypothesis, we found that the strength of affiliative relationships lowered the aggressiveness of a male towards a female, and predicted how much support a female received from a particular male in agonistic interactions with other group members. Additionally, relationship strength predicted the time that females spent co-feeding with a particular male as well as her feeding efficiency in the presence of that male. Hence, female Assamese macaques benefit from forming a social bond with a particular male by reducing the costs of competition.