Affiliative Processes and Vocal Development" CHARLES zyxwv T. SNOWDON zyxw Department zyxwv of Psychology University of Wisconsin Madison, Wisconsin 53706- 1696 The vocal communication system of many nonhuman primate species is richly com- plex with threat calls, alarm calls that in some species refer to specific predators, intergroup spacing calls, food associated calls, and others.',' Relatively few studies have focused on vocalizations mediating affiliative relationships, in part because affiliative vocalizations are softer and more cryptic and therefore difficult to observe except in captive or highly habituated wild populations. In addition, affiliative relation- ships generally occur when animals are in close proximity and therefore other modal- ities such as facial expressions or chemical signals can be used in affiliative interac- tions. In this chapter, I review briefly some of the studies on affiliative vocalizations in nonhuman primates and then move on to a topic I think is potentially more important: how affiliative processes mediate the ontogeny of vocal communication. Although my examples are drawn from nonhuman primates, the basic findings parallel recent studies on birds, cetaceans, and human children3 and suggest that affiliative interactions during development are critical for acquiring communication skills in a wide range of species. AFFILIATIVE VOCALIZATIONS Rhesus macaques (Macaca mulatta) have been the subject of most research on affiliative vocalizations with the primary focus being the vocalizations used by infants when separated from their mothers. The calls given by separated infants have been classified as affiliative by several The coo structure of macaques varies with social contexts, and monkeys separated from mothers and out of their sight give different variants of coo vocalizations than they do when separated but in sight of the mother.' The rate of coo vocalizations is different as well, with more calls being given when infants and mother are in sight of each other. In a naturalistic study of stumptail macaques (Macaca arctoides), Lillehei and Snowdonadescribed two differ- ent forms of coo vocalizations, one used by infants seeking contact with mothers and another variant when they were seeking contact with other group members. Newman' used the separation paradigm to study vocal development in several species: aThis research was supported by United States Public Health Service grants MH 29,775 and MH zy 00,177 and the University of Wisconsin Graduate School Research Committee. zyx 340