Effects of reproductive state on vocalizations in squirrel monkeys (Saimiri sciureus)

Vocalizations and behavior of a group of 6 squirrel monkeys, 2 males and 4 females, were recorded during the nonbreeding and breeding seasons. Behavioral and physical criteria were used to determine the presence of estrus. During the breeding season the types of vocalizations uttered by estrous females changed, and the adult male increased his rate of vocalizing. Err vocalizations by estrous females were associated with increased following and initiation of affiliative behavior with the adult male, and may have functioned to facilitate these interactions. Errs appeared to be related to changes in female reproductive state rather than to the behavior of others. The adult male increased vocalizations associated with sexual and aggressive behavior (squeals and cackles), primarily in response to the estrous females' persistent initiation of interactions with him. We concluded that certain vocalizations in Saimiri reflected changes in the reproductive state of males and females, and functioned to mediate changes in social bonding during the breeding season.