This and a companion project (Z01 HD001123-14) 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 structural differences to differences in age, gender, experience and response selectivity, as well as the broader factors of social context and genetic background. New findings: 1) A long-distance affiliative vocalization, the isolation peep (IP), was tested for responsiveness to species-specific differences in the acoustic details. Isolation Peeps from 2 species of squirrel monkey (Saimiri sciureus and S. boliviensis) were digitized, then entered into a library for use as playback stimuli. Eight acoustic parameters of each call were measured, and these parameters entered into a discriminant function analysis to determine whether a given call represented a weak, typical or extreme variant of one or the other species' calls. A total of 152 calls were selected as playback stimuli. Four social groups, 2 groups of each of the 2 species, were chosen as subjects. Subjects were tested in an outdoor run and were presented with 12 stimulus trials and 4 control (no stimulus) trials per session. Sessions were run daily. In all 4 groups, there was no significant difference in responding depending on whether the stimulus was from the same or the other species. Nevertheless, overall all groups, 67% of the stimulus trials had an IP response,while only 17.5% of the control trials had an IP response (p<0.01, Chi-square test). These responses from intact groups to separation calls suggests the existence of atruistic or empathic vocal behavior in this primate. The acoustic details of the stimulus signal were not found to influence the vocal response. Future work will attempt to resolve the underlying mechanism that appears to impart different sensory biases to the 2 closely-related species under study. 2) A little-examined acoustic parameter--intercall interval-- was employed in a comparative study of the cry sounds of human infants and the infants of 2 non-human primates, the rhesus macaque and the common marmoset. For each species, a 30-second segment of crying was analyzed, with the interval between expiratory cry sounds measured. For humans, 3 cries from each of 4 subject groups were examined: low-risk, preterm; high-risk, preterm; low-risk, fullterm; high-risk, fullterm. Using the Kolmogorov-Smirnov test (K-S test), significant differences were found in the distribution of intervals for all pair-wise tests of the 4 groups, except for low-risk and high-risk preterms. For the rhesus macaques, the comparison groups were mother-reared infants and nursery-reared infants. Significant differences were found in the distribution intervals between these groups, but only for males. More individuals of both groups will be analyzed to determine whether this is a consistent finding. For the marmosets, the comparison was made between young ages (under 1 month) and older ages (2 or 3 months of age). Significant differences were found in the distribution of intervals in the cries of infants from these 2 age groups. These results suggest that the temporal patterning of crying may be an important parameter for evaluating the developmental or experiential status of a crying individual.