Introduction of two wooden climbing frames as environmental enrichment for captive chimpanzees (Pan troglodytes) and its assessment

Chimpanzees in the wild spend about half of the day in trees. For their psychological well-being, it is important to provide captive chimpanzees with three-dimensional space. At the Japan Monkey Centre, seven chimpanzees are kept outdoors in a compound (776m2) during the daytime. We introduced a 4m high wooden climbing frame in June 1998. Another 8m high wooden frame was added in April 1999. In order to do the assessment of this environmental enrichment, we evaluated the contribution of these two climbing structures toward the behavioral repertories, the spacing patterns, and the activity budget. All chimpanzees used the wooden frames. The proportion of staying in the climbing structures increased from 29.1% (at the stage of no wooden frames) to 34.9% (with a 4m high structure) and to 64.3% (with an additional 8m high structure) that is comparable to the level recorded in the wild. Although no drastic change was observed in the activity budgets, the number of behavior patterns increased. These results suggest that the introduction of wooden climbing frames was an effective method of environmental enrichment for captive chimpanzees.