Lambeth, S. P., Bloomsmith, M. A. 1992. Mirrors as enrichment for the captive chimpanzee (Pan troglodytes). The Newsletter 3(3), 1.

No quantitative studies have focused on the properties of a mirror and its use as a social enrichment tool. We did an observation study, which included 239 12-minute sessions over a four month period to test the enrichment properties of a mirror. The chimpanzee subjects were housed in conventional indoor/outdoor runs that were separated by a solid wall on one side, not allowing visual access to or physical contact with neighboring conspecifics on that side. When the mirror gave subjects visual access to neighboring animals, sexual and agonistic behaviors increased, whereas play behavior decreased compared with when no mirror was present.