Cage enrichment, physiology, and behavior in nursery-reared rhesus monkeys (1989)

Clarke, M. R., Koritnik, D. R., Martin, L. N. et al.

Abstract

Calm [single-caged] control animals and stressed [single-caged] enriched animals exhibited higher cortisol values. The enriched animals had lower cortisols when they appeared calm and higher cortisols when they appeared stressed. .. Control animals exhibited the opposite pattern, and calm control animals had the overall highest cortisol values. High values in behaviourally calm control animals indicate a dissociation between physiological and behavioral reactions to environmental conditions.