Adult cortisol response to immature offspring play in captive squirrel monkeys

Variable environmental and social conditions influence hypothalamic-pituitary-adrenal activity in captive animals. Socially separated and individually housed animals generally experience increased cortisol secretion compared to animals housed with conspecifics, and social companionship can buffer the stress response when exposed to challenges such as introduction to novel environments. Nevertheless, the presence of conspecifics may also be the cause of stress because social dynamics impact individuals. Squirrel monkeys (Saimiri spp.) readily form same-sex affiliative social relationships, but in captivity, the presence of immature offspring severely disrupts affiliative associations among adults. We examined behavioral and physiological effects of the presence of immature offspring on adults by comparing two groups of adults with immature offspring to an all-adult group. We conducted behavioral observations and collected urine from adult members, and urine was assayed for cortisol at the Wisconsin National Primate Research Center. Adults in groups with immature offspring received an average of 18 play attempts per hour from the offspring, experienced a fivefold decrease in adult affiliation, and showed higher urinary cortisol levels compared to the all-adult group. A principal components analysis showed that adults characterized by receiving play attempts, rejecting play attempts, and lacking affiliative contact with other adults showed the highest mean urinary cortisol levels. Further analyses demonstrated that the persistent play attempts by immature offspring, not the resulting lack of adult huddling, were primarily responsible for the observed increase in urinary cortisol levels. Taken together, these data suggest that the disruptive effect of immature offspring produces a chronic cortisol increase in captive adult squirrel monkeys.