Intergroup encounters among free-ranging vervet monkeys.

High-ranking vervet monkeys threatened the members of other groups more than did low-ranking individuals, while only low-ranking females and juvenile males interacted affinitively with the members of other groups. Adult males were most aggressive during intergroup encounters with groups from which males transferred. In contrast, females were most aggressive to groups from which males were not observed to transfer. It is postulated that the behavior of individuals during intergroup encounters may be related to benefits derived from excluding intruders from the group's resources. Furthermore, it seems possible that relations between groups are influenced by previous male transfers, and that female aggression affects the distribution of male movement between groups.