Toward a general model for male-male coalitions in primate groups

Abstract

Of the many forms cooperation can take in nonhuman primates, the formation of coalitions is perhaps the most spectacular. Coalitions can be defined as coordinated attacks by at least two individuals on one or more targets, often preceded by signaling between the attackers (side-directed communication: de Waal & van Hooff 1981, de Waal 1992a; cf. Smuts & Watanabe 1990). They may serve to protect against attacks by more powerful individuals, to defend or gain access to resources or to acquire the dominance rank of the target individual. Animals forming the coalitions often are friends, as defined by Silk (2002c), although this is not true in all cases (Noë & Sluijter 1995). Friendships that involve coalitions are commonly called alliances (Harcourt & de Waal 1992a).