This and a companion project (Z01 HD01123-10) investigate auditory communication in primates. The overall goal of these studies is to provide a comprehensive understanding of primate auditory communication in terms of development, neural mechanisms, endocrine factors, and social context. Two species, the squirrel monkey and the common marmoset, are the main subjects of study, with additional data collected from other species where appropriate. The present project studies primate communication from a bioacoustic and ethological perspective, focusing on the detailed acoustic structure of vocalizations produced in natural settings, and the relationship of structure differences to differences in age, gender and experience, as well as the broader factors of social context and genetic background. New findings in FY2000 focused on the perceptual side of auditory communication, using playback techniques to examine perceptual preferences as measured by phonotaxis (approaching the direction of the sound source) and vocal responding. In two studies, a close-range affiliative vocalization given mainly by adult female squirrel monkeys, the ?chuck,? was tested for responsiveness based on the familiarity of the sound (due to the ?vocal signature? quality of the chucks of individual vocalizers) to the listener. Squirrel monkeys of various ages when tested showed differential responding to familiar chucks only after 3 years of age. Younger animals (1.5-2.0 years of age) showed a similar, but less robust, tendency, while younger animals failed to show any preference for the chucks of familiar group members. A second study, using only adult females, found that females vocally respond with short-latency (< 4 sec) chuck responses upon hearing the chucks of affiliative partners within their group, somewhat less often to the chucks of group members who are not affiliative partners, and significantly less to the chucks of unfamiliar individuals. These findings support the conclusion that engaging in chuck exchanges is a learned behavior that is gradually perfected over the first 3-4 years of life, and is used mainly to provide acoustic information of the location of affiliative partners (and possibly related kin) in the wild. Future studies will attempt to determine the neurophysiological basis for this discriminative capability.
