The role of peers in modifying behavioral distress and pituitary-adrenal response to a novel environment in year-old rhesus monkeys

The effects of a peer's presence were examined for 9 mother-reared rhesus monkeys (mean age=12 months). Subjects were captured from their social groups and placed in single cages for 24 hr under each of 4 conditions: Alone, with Mother, with a Peer from the Same Group, or with a Peer from a Different Group. Plasma cortisol and behavioral data were obtained. Thirty min after capture the presence of a peer from a different social group produced elevations in plasma cortisol greater than those observed in all but the Alone condition. This effect was not apparent 24 hr later. Furthermore, by 22 hr after capture the presence of a peer from either social group significantly reduced agitated behavior, as compared to responses observed when subjects were housed alone. These subjects thus readily habituated to the less familiar peer to whom they initially responded. Physical contact and whoo calling clearly differentiated responses to peer from mother, suggesting that the calming effect of a peer's presence was not sufficient that the peer serve as a surrogate attachment figure. The results indicate the role of peer conspecifics in modifying responses to stressful situations in young group-reared rhesus monkeys.