Reinhardt, V., Hurwitz, S. 1993. Evaluation of social enrichment for aged rhesus macaques. Animal Technology 44, 53-57.

The effect of a compatible companion on the behaviour and bodyweight of eight previously single-caged, 31-36 years old rhesus macaques was assessed 16 months after pair formation. The aged subjects preferred to stay in close proximity with their companion even though this reduced their available cage space. They spent on average 21% of the time (3 one-hour observations in the morning, at noon and in the afternoon) interacting with the companion in noninjurious species-typical ways. Affiliative interactions, i.e., grooming and huddling, accounted for more than 99% of total interaction time. Sharing a cage with a compatible con-specific did not jeopardize the subjects' general health, as reflected in their body weight development. It was concluded that single-caged rhesus macaques readily adapt to living with a companion who provides them with a species -adequate environment for the expression of their inherent social disposition.