Sexual Segregation, Cliques, and Social Power in Squirrel Monkey (Saimiri) Groups

Abstract

AbstractThis report presents two studies of captive squirrel monkeys living in mixed-sex social groups: In the first study, we quantified social interaction patterns and spacing in two groups during their regular daily feeding period. Dispersal of food was rapid, owing to the animals' tendencies to drop items on the cage floor, and competitive interactions were infrequent. Adult males and females were spatially segregated, and between-sex interactions were relatively infrequent. Dyadic proximity data indicated that each group contained several cliques of from two to three individuals, usually of the same sex. Members of a clique not only spent more time near each other, but favored the same areas in the cage, even when they were not in proximity. Measures of proximity and agonism were positively correlated. In the second study, the same groups were presented with either one or two bottles of fruit drink, a highly desired, non-dispersible resource, or with one or two bottles of plain water. During water-bottle sessions, between-sex interactions were no more frequent or agonistic than they were in the normative study; in the highly competitive fruit-drink sessions, however, males frequently directed agonistic behavior against females and against each other, and they successfully dominated access to the fruit-drink bottles. In contrast, female agonism was directed mainly toward other females. Our observations suggest that membership in a clique may provide a competitive advantage. In one group, a clique consisting of a mother and her daughter successfully excluded other females from the fruit-drink bottles; in another group, the only females to compete vigorously against males were members of the same clique; after one of the two males in this group was removed, females for the first time made occasional joint attacks on the remaining adult male, and he appeared to become less assertive and successful in competitive tests. We suggest that the social and spatial peripherality of males is not simply the result of coercive exclusion by females, but also reflects a "choice" by males to avoid interacting with females under most circumstances. When male motivation is strong, however, they readily approach females, aggress against them, and assert themselves successfully in competitive interactions, even against a substantial female majority.