Behavioral and adrenocorticoid responsiveness of squirrel monkeys to a live snake: Is flight necessarily stressful?

Abstract

Bolivian and Guyanese squirrel monkeys were assessed for responses to a live boa constrictor snake and to the novelty/disturbance associated with this presentation. Wild-born animals from adult groups which contained males, females, and pregnant females were tested during both individual and group conditions. The latter condition involved placing the empty or snake-occupied wire-mesh stimulus box on top of the group's home cage. In the individual conditions, an animal was removed from the social group cage and placed alone in a vertically oriented test cage with the stimulus box on top. Spatial and behavioral measures were recorded during these 30-min experimental sessions, and blood samples for plasma cortisol analysis were obtained at the end of each weekly session. Blood samples were also taken during undisturbed conditions 1 week before and after the experimental period. All monkeys revealed agitated behavior in the presence of the snake. In contrast, the cortisol levels in response to the snake and empty box were not different for any group of animals. However, the mean of the two individual tests was greater than the mean of the group tests for males, females, or pregnant females. These data support previous studies which indicate that wild-born squirrel monkeys clearly respond with behavioral distress to a live snake. Although cortisol elevations were not specifically produced by exposure to the snake, the responsiveness of the squirrel monkey pituitary—adrenal system to novelty was demonstrated, as all types of monkeys showed significant elevations to the disturbance/novelty of the individual tests.