Friendship Amongadult Female Bluemonkeys ( Cercopithecusmitis )

A study group of blue monkeys in the Kakamega Forest, Kenya, provides data on friendly relationships between adult females. Females are invariably antagonistic toward members of other groups, and collaborate with their own groupmates in defending territorial boundaries. Females are primarily responsible for these aggressive intergroup encounters, which occur every other day on average. Encounters are often immediately followed by intense grooming among adult females, which gives the impression of reinforcing the collaborative team. In some lower-density populations, intergroup aggression is rare; in these populations, and at Kakamega as well, female groupmates may provide other or additional services, such as protection against predators or aggressive males. Friendships among females of a single group are differentiated. Individuals interact with certain grooming and proximity partners much more than others. Despite low rates of agonism, blue monkey females also show stable