Interventions and alliance formation between female Japanese macaques, Macaca fuscata, during homosexual consortships

The purposes of this study were to assess whether homosexual behaviour promotes alliance formation between sexual partners and whether individuals engage in homosexual behaviour to form alliances. Data were collected during pre- and post-consortship baseline periods and during 21 of 28 different homosexual consortships observed ad libitum. These consortships involved 14 female Japanese macaques, Macaca fuscata, living in a captive, bisexual group of 37 individuals. Non-kin females intervened for each other significantly more when in homosexual consortships than during the baseline periods. Consort partners did not intervene for other sexually mature, non-kin females in this manner. Interventions were not performed as sexual solicitations. Subordinate consort partners were equally likely to receive alliance support against dominant and subordinate targets, and they routinely received support against targets with whom they had ambiguous dominance relationships. Compared to the baseline periods, subordinate partners directed more agonistic behaviour to other group members, who, in turn, avoided agonistic interactions with these females. Some consorting females, especially subordinate partners, temporarily increased in dominance upon receiving support against dominant targets, or targets with whom they shared an ambiguous dominance relationship. Absence of preference for high-ranking consort partners, coupled with the bi-directional flow of most affiliation within consortships, suggested that choice of same-sex partners was principally based on mutual sexual attraction and not on their potential utility as allies. These data suggest that homosexual behaviour promotes alliance formation between sexual partners, but that individuals do not engage in homosexual behaviour for the express purpose of forming alliances. (C) 1996 The Association for the Study of Animal Behaviour