Outdoor access: The behavioral benefits to chimpanzees (1998)

Baker, K. C., Ross, S. K.

Abstract

When compared to the results of ameliorative environmental enrichment techniques furnished to the indoor-housed subjects, the small outdoor groups of [two or three] chimpanzees showed broader and more dramatic improvements in well-being. Animals with outdoor access showed significantly less abnormal behavior (e.g., coprophagy, regurgitation/reingestion), less yawning, and more self-grooming.