Human interaction as environmental enrichment for chimpanzees (Pan troglodytes) and other primates is widely promoted and believed to be of value, but has been subject to little objective evaluation. This study assessed the effects of positive human interaction (eg relaxed treat feeding, playing, and other forms of social interaction compatible with personnel safety) on the behaviour of adult chimpanzees. Subjects were housed indoors in groups of two or three individuals. The level of interaction during routine care and management (ie in the process of cleaning, feeding, and monitoring) represented the baseline condition. The test condition involved a familiar caretaker spending an additional 10 mins per day, 5 days a week, with each chimpanzee. This study was designed to assess carry-over effects of interaction on behaviour outside the context of care staff presence. Therefore, in all phases of the study, data (97 h of focal animal sampling) were collected only when caretakers were absent from the building. During the increased human interaction phase, the chimpanzees groomed each other more and showed lower levels of the following behaviours: regurgitation/reingestion, other oral abnormal behaviours, inactivity, and reactivity to the displays of neighbouring groups. A trend towards reduced agonistic display was also detected. Attempted interactions with the observer shifted significantly from predominantly aggressive to predominantly affiliative in nature. These results suggest that simple, unstructured affiliation between humans and chimpanzees should be a valued component of behavioural management.
