Affiliative processes and vocal development.

Affiliative behavior is often expressed through communication, and the nature of affiliative interactions affects the ontogeny of communication. I presented three phenomena that demonstrate the importance of affiliation in vocal development in marmosets and tamarins, but the results have parallels in many other species including birds, dolphins, and humans. Pygmy marmosets use trill-like vocalizations to maintain contact with other group members. Individuals change subtle aspects of call structure when they encounter new social groups or acquire a new mate. This process of vocal accommodation is common in many other species. Infant pygmy marmosets go through a stage of "babbling." producing long sequences of vocalizations that have several similarities to the babbling of human infants. Babbling infants receive more social attention than nonbabbling infants, and these social interactions may shape vocalizations towards more adult forms. In adult cotton-top tamarins, food-associated vocalizations communicate the presence and quality of food. However, reproductively inhibited juveniles and subadults use many other types of calls in feeding situations and display a high proportion of imperfect forms of adult food-associated calls. When subadult monkeys are paired with new mates and change their reproductive status, they rapidly (within 3-6 weeks) display both adult structure and adult usage of food-associated calls, suggesting that affiliative processes can both facilitate and inhibit vocal ontogeny. Three mechanisms of how social interactions affect communication (multimodal stimulation, attentional focus, and reinforcement) were proposed and illustrated through examples of parrots learning English labels for objects and attributes and infant cotton-top tamarins acquiring food-associated vocalizations.