Responses of human-reared monkeys to strange simian calls.

The responses of 16 young (10-12 month and 19-20 month) hand-reared rhesus monkeys to rhesus vocalizations heard for the first time were recorded. The vocal stimuli were: (1) a "clear call" of a noncolony adult; (2) a "bark" of a noncolony adult; (3) a "bark" of a noncolony juvenile; and (4) a "bark" of a colony juvenile. Behavior was video-tape recorded for 5-min periods preceding and following the calls and scored according to standard categories. The characteristic response to the stimuli was a sharp reduction in overt behavior. Reaction to the adult sounds was greater than to the juvenile sounds.