Behavioral responses to species-specific warning calls in infant squirrel monkeys reared in social isolation.

Six infant squirrel monkeys were reared in social isolation. They responded differentially to playbacks of two species-specific alarm calls. The reaction to the alarm peep, the warning call to bird predators, was a prompt flight to the mother surrogate and essentially resembled the respective behavior of mother-reared infants. The responses to yapping, the alarm call to terrestrial predators, were less clear-cut and habituated soon. However, when yapping was played back in connection with the presentation of a reference object, both subjects tested in this way clearly avoided the object and preferred contact with the mother surrogate while they thoroughly explored an object presented with a control tone. From this it can be concluded that the perception of both alarm calls is innate. In addition, the method of behavior-contingent playback of vocalizations simulates the learning process by which the visual perception of terrestrial predators of the habitat is acquired.