THE BEHAVIOR OF SINGLY-CAGED, YEARLING RHESUS-MONKEYS IS AFFECTED BY THE ENVIRONMENT OUTSIDE OF THE CAGE

Numerous studies have demonstrated that the behavior of singly caged l aboratory primates can be positively affected by inanimate enrichment within the cage. The environment outside of the cage may also influenc e the behavior of singly caged rhesus monkeys. To test this, we compar ed two cohorts of yearling rhesus (Macaca mulatta); one that had only limited stimulation in the environment outside of the cage (singly cag ed in indoor rooms), and one that had considerable naturalistic and so cial stimulation in the extra-cage environment (singly caged in an out door building). Half the animals in each housing condition received a three-phase enrichment program and the rest served as controls. Subjec ts that had sensory access to social groups of conspecifics spent sign ificantly more time drinking, feeding, and behaving abnormally, and si gnificantly less time inactive and playing than did subjects that only had sensory access to other singly caged rhesus. Enriched subjects in both settings spent significantly more time playing and less time sel f-grooming than did controls. There was also a significant interaction for time spent in play, with enriched subjects living indoors playing the most. Although subjects that received considerable stimulation fr om outside of the cage spent more time engaged in abnormal behavior, m ost was pacing; usually in response to human manipulations of the othe r monkeys in the colony. Subjects housed indoors, with limited extra-c age stimulation spent less time pacing, but more time in potentially i njurious abnormal activities, Among enriched subjects only, those hous ed indoors spent less time drinking and behaving abnormally and more t ime playing and using enrichment. Inanimate enrichment within the cage led to consistent positive changes in behavior for singly housed rhes us. Although the environment outside of the cage was shown to influenc e behavior, it was not clear whether exposure to numerous social and n aturalistic stimuli was preferable to more limited stimulation for pro moting well-being. Although the increased stimulation associated with a complex extra-cage environment is usually considered beneficial, not all such stimulation is positive. Frequent disturbances to social gro ups in view of singly caged subjects resulted in increased pacing, but the complex extra-cage environment also provided subjects with more o pportunities to express and observe components of the species-typical behavioral repertoire.