Pairing laboratory-housed adult male rhesus macaques (Macaca mulatta): Success rates in relation to behavioral response and duration of visual contact

While the benefits of pair housing have been well documented, less is known about increasing success in adult male macaque pair introductions. In this retrospective study, 95 unfamiliar adult male macaque (Macaca mulatta) pairs were examined to determine whether duration of visual contact, behavior, age, and weight were associated with success rate, with “success” defined as two weeks in full tactile contact without excessive behavioral indicators of incompatibility or injury requiring clinical treatment or care. Overall, the unfamiliar adult male pairs achieved a success rate of 72 % and wounding requiring medical attention was rare (2 %). A significant negative relationship between pair success and time in visual contact for pairs was found. Pairs who moved into tactile contact within 48-hours showed more positive social behaviors in protected and full contact and had a high rate of success (91 %), while those who exhibited negative social behaviors were maintained in visual contact for longer. Nevertheless, rapid signs of compatibility were not necessary for the formation of successful pairs. While social introduction success rates steadily declined with increased periods of maintained visual contact, longer durations of 3 days to 1 week (70 %), and 8+ days (58 %), were still accompanied by high to moderate success, respectively. These results indicate that when negative social behavior is present early in visual contact success may be expected to decrease, but it is not necessarily indicative of incompatibility. Providing extra time in visual contact can reduce overall incidences of single housing.