Food search demand effort effects on behavior and cortisol in adult female squirrel monkeys.

Laboratory-born, group-housed, ovariectomized adult female squirrel monkeys (Saimiri sciureus) were exposed to feeding conditions in which the availability and accessibility of food were altered. Both high- and variable-demand feeding conditions were utilized. The variable-demand condition required alternating periods of high effort (120% of normal daily intake presented) and low effort (600% of normal daily intake presented) to obtain food for 10-12 weeks. An additional group was exposed solely to the high-demand condition for 10 weeks. Blood samples were obtained weekly, and behavioral observations were conducted daily. In the variable-demand condition, plasma cortisol was elevated above baseline during the periods of high effort. For the constant high-demand group, cortisol was elevated for the duration of the experimental treatment. Contact with other animals, as well as a species-specific inactive posture, decreased as a result of exposure to high demand. Maintenance of body weight indicated that nutritional deprivation did not occur. The imposition of increased food-seeking efforts provides an ecologically relevant and noninvasive method of producing chronic stress in the squirrel monkey.