Pickle barrels as enrichment objects for rhesus macaques.

Two breeding groups of rhesus monkeys (Macaca mulatta) housed in outdoor enclosures on Key Lois island were observed for 84 hours. Instantaneous scan sampling of a focal animal was used to gather data to test hypotheses concerning frequencies of agonistic and affiliative behaviors as well as differential use of pickle barrels as enrichment objects. Type of barrel used, behavior, and age/sex class of the animal were noted. Barrels were arranged three ways: unattached, on a swivel, and stationary. The behaviors of animals in an enriched environment were compared with control condition animals, which did not have pickle barrels. Animals in an enriched environment accounted for 60.8% (n = 56) of total affiliative contact, 62.2% (n = 399) of total social grooming, and 26% (n = 5) of total agonistic noncontact. A total of 134 scans of barrel use were observed. Analyses of the data showed that swivel and stationary barrels were used the most (55% of all scans of barrel use). Yearlings, juvenile females, and old males used barrels most often (82.8% of all scans of barrel use), although they constituted only 39% of the enriched environment population. In this study, pickle barrels provided enrichment for young and old animals of both sexes.