VOCALIZATIONS OF RHESUS (MACACA-MULATTA) AND JAPANESE (M-FUSCATA) MACAQUES CROSS-FOSTERED BETWEEN SPECIES SHOW EVIDENCE OF ONLY LIMITED MODIFICATION

Two rhesus and two Japanese macaque infants were cross-fostered betwee n species in order to study the effects of auditory experience on voca l development. Both the cross-fostered and normally raised control sub jects were observed over the first 2 years of life and their vocalizat ions were tape-recorded. We classified 8053 calls by ear, placed each call in one of six acoustic categories, and calculated the rates at wh ich different call-types were used in different social contexts. Speci es differences were found in the use of ''coo'' and ''gruff'' vocaliza tions among control subjects. Japanese macaques invariably produced co os almost exclusively. In contrast, rhesus macaques produced a mixture of coos and gruffs and showed considerable interindividual variation in the relative use of one call type or the other. Cross-fostered Japa nese macaques adhered to their species-typical behavior, rarely using gruffs. Cross-fostered rhesus subjects also exhibited species-typical behavior in many contexts, but in some situations produced coos and gr uffs at rates that were intermediate between those shown by normally r aised animals of the two species. This outcome suggests that environme ntally mediated modification of vocal behavior may have occurred, but that the resulting changes were quite limited. (C) 1993 John Wiley & S ons, Inc.