Evaluation of environmental and intrinsic factors that contribute to stereotypic behavior in captive rhesus macaques (Macaca mulatta).

Full body repetitive behaviors, known as motor stereotypic behaviors (MSBs), are one of the most commonly seen abnormal behaviors in captive non-human primates, and are frequently used as a behavioral measure of well-being. The main goal of this paper was to examine the role of environmental factors (i.e., foraging enrichment and socialization) and intrinsic factors (i.e., temperament and origin) in the development of MSB in rhesus macaques living in cages. MSB was assessed during short annual observations in which a trained observer recorded a monkey's behavior for 5 min, followed by a 3-min novel object test. Data were collected over 11 years, totaling 9805 observations. We compared MSB for animals with and without foraging enrichment, and across three socialization conditions: full contact pairing, protected contact socialization (partners physically separated by widely spaced bars), and single housing. In addition, we evaluated whether individual differences in response to a novel object and ancestral origin (i.e., China vs. India), predicted MSB expression during the annual observations. Data were analyzed using generalized mixed effects modeling, with the best fitting models chosen using Akaike Information Criterion. Subjects were at lowest risk for MSB when a foraging device was present (p < 0.05), and when in full contact social housing (p < 0.001). There was no statistically significant difference in MSB between subjects that were single housed and subjects housed in protected contact pairs. In addition, subjects that never touched the novel object were significantly less likely to exhibit MSB than those that touched the object immediately (p < 0.001) or within 3 min (p < 0.001). Finally, monkeys with some degree of Chinese ancestry were significantly more likely to display MSB than Indian-origin monkeys (p < 0.05). These results add to the growing body of literature on factors that can contribute to the development of MSB.