Effects of nonmaternal restraint on the vocalizations of infant rhesus monkeys (Macaca mulatta)

This study explored the effects of restraint by females other than the moth er on the vocalizations of infant rhesus macaques (Macaca mulatta) in a cap tive social setting. In this species, females are very attracted to young i nfants and will frequently approach! groom, and hold the infant. Incompeten t handling, abusive behavior, or extended periods away from the mother that prevent the infants from nursing represent potentially significant risks f or infants. Vocal responses to such risky conditions appear to be the infan ts' only means to promote a return to their mothers. We examined the associ ation between the severity of the threat posed to the infant and the nature of its vocal response to restraint, and whether the infants' calls influen ced the behavior of their mothers or captors. The results suggest that situ ations posing greater risks for the infants, i.e., longer periods of restra int, were associated with a greater use of noisy screams. Furthermore, moth ers' responding was associated with a greater use of noisy screams as well. The mothers' reactions, however, could be described as cautious, and consi sted mostly of closer monitoring; such tempered response might be related t o the risk of injury to the infant that could result from a more forceful a nd direct attempt at retrieval. Am. J. Primatol. 53:33-45, 2001. (C) 2001 W iley-Liss, Inc.