Environmental enrichment of brown capuchins (Cebus apella): Behavioral andplasma and fecal cortisol measures of effectiveness

No consensus exists about the quantity and variety of environmental enrichm ent needed to achieve an acceptable level of psychological wellbeing among singly housed primates. Behavioral and plasma and fecal cortisol measures w ere used to evaluate the effectiveness of four levels of toy and foraging e nrichment provided to eight wild-caught, singly housed adult male brown cap uchins (Cebus apella). The 16-week-long study comprised six conditions and began with a 4-week-long preexperimental and ended with a 4-week-long poste xperimental period during which the subjects were maintained at baseline en richment levels. During the intervening 8 weeks, the subjects were randomly assigned to a sequence of four 2-week-long experimental conditions: contro l (baseline conditions), toy (the addition of two plastic toys to each cage ), box (access to a foraging box with food treats hidden within crushed alf alfa), and box & toy (the addition of two plastic toys and access to a fora ging box). Behavioral responses to changes in enrichment were rapid and ext ensive. Within-subject repeated-measure ANOVAs with planned post hoc contra sts identified highly significant reductions in abnormal and undesirable be haviors land increases in normal behaviors) as the level of enrichment incr eased from control to toy to box to box & toy. No significant behavioral di fferences were found between the control and pre- and postexperimental cond itions. Plasma and fecal cortisol measures revealed a different response to changing enrichment levels. Repeated-measure ANOVA models found significan t changes in both these measures across the six conditions. The planned pos t hoc analyses, however, while finding dramatic increases in cortisol titer s in both the pre- and postexperimental conditions relative to the control condition, did not distinguish cortisol responses among the four enrichment levels. Linear regressions among weekly group means in behavioral and cort isol measures (n = 16) found that plasma cortisol was significantly predict ed by the proportions of both normal and abnormal behaviors; as the proport ion of normal behaviors increased, the plasma cortisol measures decreased. Plasma cortisol weekly group means were also significantly and positively p redicted by fecal cortisol weekly group means, but no behavioral measure si gnificantly predicted fecal cortisol weekly group means. In sum, these find ings argue strongly that access to a variety of toy and foraging enrichment positively affects behavioral and physiological responses to stress and en hances psychological well-being in singly housed brown capuchins. Am. J. Pr imatol. 48:49-68, 1999. (C) 1999 Wiley-Liss, Inc.