DEVELOPMENT OF VOCAL RESPONSES IN INFANT COTTON-TOP TAMARINS

Abstract

AbstractTo examine the development of production, comprehension and usage of chirp vocalizations in infant cotton-top tamarins, we designed four experimental settings to elicit five of the eight chirp types of adult cotton-top tamarins. We tested non-reproductive adult pairs and family groups before and after the birth of infants. We observed responses of infants in family groups during the first 20 weeks following birth. The five chirp types were rarely given in control conditions, but each type occurred at significant levels among adults and subadults immediately following presentation of an appropriate stimulus. Each chirp type was specific to one experimental manipulation. We found no differences between non-reproductive pairs and families prior to the birth of infants, but two chirp types were produced at significantly lower rates following the birth of infants. Infants produced a form of chirp (prototype chirp) not seen in adults, but infants rarely produced adult forms of chirps. If an adult-appropriate chirp was produced by an infant in one session, there was a low probability of that chirp appearing in subsequent tests with the same infant. Infants used most frequently the form of chirp (D chirp) that was most frequently directed toward them by adults, and infants reduced their rates of prototype chirps following presentation of visual and auditory alarm stimuli. Although infant tamarins under 20 weeks of age appear unable to use adult types of chirps consistently, they did produce chirps with adult form, and they appeared to show some comprehension of chirps produced by adults.