Maternal discrimination of infant vocalizations in squirrel monkeys

Responses of mother squirrel monkeys to vocalizations of their own and other infants were examined to determine whether mothers could discriminate their infants on the basis of auditory cues. Thirty mothers, whose infants ranged in age from one to seven months were tested in three conditions in which their own infant, a different infant, and no infant served as the stimulus. Mothers were tested in an enclosed alleyway with opaque end panels behind which stimuli were placed. The quantity and quality of maternal responses clearly differed in the three conditions and indicated that mothers recognized their own infants. Differences in maternal vocalizations were the most pronounced. All but one type of vocalization increased in the own-infant condition; the exception, a high-pitched shrill, decreased. Mothers also spent more time near the stimulus and were more active when tested with their own infants.