Vocal Interactions Between Unfamiliar Groups of Captive Cotton-Top Tamarins

Abstract

Vocal interactions between captive groups of cotton-top tamarins (Saguinus oedipus oedipus) were studied by simulating encounters between unfamiliar groups. The doors were opened between pairs of colony rooms resulting in an increased amplitude of the normal intragroup vocalizations of an unfamiliar group. After several seconds, some groups began Long Calling bouts, complex exchanges of calls accompanied by behavioral patterns seen only in encounters between unfamiliar groups. The behavior patterns included increased scent marking and piloerection and decreased huddling compared with a control condition. Both the behavioral patterns and the vocalizations were similar to those observed in intergroup encounters in the wild. The vocalizations of each group were recorded on separate channels and subsequently identified through a real time spectrum analyzer. Four different calls appeared at significantly higher rates during the Long Calling bout: Females tended to give normal Long Calls and males tended to give F chirps. F chirps progressed into F Chirp trills which were also given primarily by males. F Chirp-Whistle vocalization, a combination of the F Chirp and the Normal Long Call, were given equally by both sexes. A surprising result was that only mated pairs without offspring participated in the Long Calling bouts. Family groups showed little vocal or behavioral response to hearing acoustically unfamiliar groups. Information theory analysis was used to analyze the transitions between call types and between groups. The production of several call types was shown to be dependent on both the preceding call type and the group of origin of that call. In general the progression from one call type to another occurred within the same group, while the other, unfamiliar group tended to repeat the call that it heard from the first group. The results are discussed in the context of the known social structure of the tamarins in the wild and in the context of the vocal exchanges of avian species with similar social systems. Continued fine-grain analysis of vocal exchanges should lead to an enhanced understanding of the structure and social complexity of vocal communication in nonhuman primates.