Coalition formation among male Barbary macaques (Macaca sylvanus)

A coalition is formed when one animal intervenes in an ongoing conflict bet ween two parties to support one side. Since support of one party is also an act against the other party, coalitions are triadic interactions involving a supporter, a recipient, and a target. The purpose of this study was to t est which of three possible theories explains coalition formation among mal e Barbary macaques: 1) Males support kin to enhance their indirect fitness (kin selection). 2) Males support nonkin to receive future reciprocal suppo rt (reciprocal altruism). 3) Males pursue self-interests and immediately be nefit via nonkin support (cooperation). Coalition formation was investigate d among 31 semi-free male Barbary macaques in the Salem Monkey Park, German y during the mating season. The results show: 1) Males intervened more ofte n in dyadic conflicts in which a related opponent was involved and supporte d related opponents more than unrelated opponents. Close kin supported each other more often than distant kin. 2) Some evidence for reciprocal support was found. However, reciprocity was probably a by-product of targeting the same individuals for dominance. 3) Coalition formation among nonkin is bes t interpreted as cooperation, based on self-interests. Male Barbary macaque s seem to intervene more often to stabilize and less often to improve their rank. Although our data were limited, the results revealed that kin suppor t, reciprocal support, and cooperative support were all involved in coaliti on formation among male Barbary macaques. (C) 2000 Wiley-Liss, Inc.