Reinhardt, V. 1991. Social enrichment for aged rhesus monkeys who have lived singly for many years. Animal Technology 43, 173-177.

There is widespread concern that aged rhesus monkeys who have been housed singly for a long time would do better living alone than sharing a cage with a companion. Ten female and five male rhesus monkeys, 22 to 33 years old and deprived of physical contact with any other conspecific for more than 10 years, were socialized with weaned infants or with each other using two standard methods of pairing. Pairing was associated with a total of 7 non-injurious aggressions during the first hour. Pairs were compatible in every case throughout a one year follow-up period. The aged monkeys' body weight three weeks after pairing were on average 0.8% greater than one week before pairing, suggesting that their well-being was not jeopardized by the presence of a compatible companion.