Mother monkeys' (Macaca nemestrina) responses to infant vocalizations.

Strnamary.-2 mother monkeys (Macaca nemestrina) separated from their infants, 2 adult females without young and 2 adult males were studied to determine activity (pacing) and vocalization in response to taped monkey calls. Stimulus tapes were prepared from two different calls of each of the rwo infant monkeys and a call of an adult female monkey. Mother monkeys separated from their infants were always more active and vocal than either non-mother female monkeys or males, and their activity and response vocalizations increased during presenrations of infant calls. There was no evidence that mothers responded differentially to the calls of their own infants. An increasing number of descriptive sc~tdies cacalog vocalizations emitted by primates and describe situations in which they occur (Andrew, 1762; Rowel1 & Hinde, 1762; Icani, 1963; Moynihan, 1966), but none experimentally tescs the effects of specific vocalizations of one primate upon another. As Marler (1965) pointed out, "speculations are poorly substanciaced even by observations . . . only by synthesizing sound signals chac are modified in various ways and presenting them to animals is it possible to show which of the properties of sounds are required co evoke the appropriate test response and which are unnecessary." Jensen and Tolman (1762) demonstrated that locomotor activity (pacing) of mother macaques was greatest when sensory access to their infants was least. Mothers who could not see their infants reduced cheir activity when they could hear them. This and other stitdies in which artificially presented vis~lal stimuli were used (Butler & Woolpy, 1963; Miller, et al., 1966; Sackett, 1766) suggested presenting taped vocalizacions of infants and measuring mothers' locomotor responses. A preliminary test of one mocher elicited a vocal response. Therefore, we used vocalization count as a second response measure. The hypotheses tested were chat mothers who were temporarily separated from their infancs would reduce their locomotion during the caped vocalizacions of cheir own infancs and chac the responses of mothers, non-mothers and males would differ from one anocher.