While there is evidence that learning plays a role in the development of the correct usage of certain vocalizations in several species of monkeys and apes, there are few studies that have demonstrated such plasticity in the production of calls. The present research investigates developmental complexity in primate vocal communication. Behavioral data, tape-recordings, and computer-aided spectrography will be used to study the acquisition and significance of pigtail macaque (Macaca nemestrina) vocal "signatures." The project focuses on recruitment screams, vocalizations that have been found to designate events and objects in the animals' external environment and that thus are rudimentarily semantic. Calls used in the recruitment of allies during fights require knowledge of kinship and dominance relationships in the group and are therefore ideal to test hypotheses that learning may be involved in the development of nonhuman primate vocal behavior. These calls have "signature" information in their acoustic structure that may serve to identify kin groups. Foster-reared infants will be studied for evidence that they acquire the signature of their adoptive matriline. The long-term aim of this research on the vocal communication of monkeys is to explore cognitive dimensions of primate behavior that may ultimately provide insights into the evolutionary origins of human language. Results should also contribute to a better understanding of the criteria for appropriate primate models for studies of language acquisition.
