Effects of Species-Specific Vocalizations On the Behaviour of Surrogate-Reared Squirrel Monkeys

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Abstract
This is a contribution to the study of the communicative behaviour in a primate, the squirrel monkey (Saimin). It will be shown whether socially inexperienced infants respond differentially to species-specific vocalizations. Six squirrel monkeys were separated from their mothers and conspecifics on the day of birth and surrogate-reared up to their 3rd month of age. In order to counteract general deprivation effects, the subjects received visual, auditory and vestibular stimulation, in addition to the constant presence of the mother surrogate and manipulanda. From the 2nd week on subjects were presented a test object 3-6 times daily. The object was so designed as to elicit behaviour which would usually be directed to conspecifics. When the subjects were able to locomote freely in their cage and approach the object on their own, the following experiment was carried out: Upon each physical contact by the subject with the object, a sound was played back by a loudspeaker hidden in the object. During any 8-min. session only one of five preselected sounds was used. The effect of two vocalizations, caw and cackle, known to be aversive in squirrel monkey groups, was compared to that of two non-aversive ones, twitter and play peep, and a neutral control tone. Caw and cackle resulted in low overall contact and less varied and less playful activities toward the test object. Subjects also were facing the objects more from a distance and spent more time in contact with the mother surrogate as their security figure. Twitter and play peep resulted in an opposite pattern. These findings indicate a genetically preprogrammed basis for perception and processing of species-specific vocalizations. This is a contribution to the study of the communicative behaviour in a primate, the squirrel monkey (Saimin). It will be shown whether socially inexperienced infants respond differentially to species-specific vocalizations. Six squirrel monkeys were separated from their mothers and conspecifics on the day of birth and surrogate-reared up to their 3rd month of age. In order to counteract general deprivation effects, the subjects received visual, auditory and vestibular stimulation, in addition to the constant presence of the mother surrogate and manipulanda. From the 2nd week on subjects were presented a test object 3-6 times daily. The object was so designed as to elicit behaviour which would usually be directed to conspecifics. When the subjects were able to locomote freely in their cage and approach the object on their own, the following experiment was carried out: Upon each physical contact by the subject with the object, a sound was played back by a loudspeaker hidden in the object. During any 8-min. session only one of five preselected sounds was used. The effect of two vocalizations, caw and cackle, known to be aversive in squirrel monkey groups, was compared to that of two non-aversive ones, twitter and play peep, and a neutral control tone. Caw and cackle resulted in low overall contact and less varied and less playful activities toward the test object. Subjects also were facing the objects more from a distance and spent more time in contact with the mother surrogate as their security figure. Twitter and play peep resulted in an opposite pattern. These findings indicate a genetically preprogrammed basis for perception and processing of species-specific vocalizations.