Effects of Human Management Events on Conspecific Aggression in Captive Rhesus Macaques (Macaca mulatta)

Conspecific aggression in outdoor-housed rhesus macaques (Macaca mulatta) at primate research facilities is a leading source of trauma and can potentially influence animal wellbeing and research quality. Although aggression between macaques is a normal part of daily social interactions, human presence might affect the frequency of various behaviors and instigate increases in conspecific aggression. We sought to determine how and which human management events affect conspecific aggression both immediately after an event and throughout the course of a day. From June 2008 through December 2009, we recorded agonistic encounters among macaques living in 7 social groups in large outdoor field cages. Behavioral data were then synchronized with specific management events (for example, feeding, enclosure cleaning, animal catching) that occurred within or near the enclosure. By using an Information Theoretical approach, 2 generalized linear mixed models were developed to estimate the effects of human management events on 1) aggression after individual management events and 2) daily levels of aggression. Univariate analysis revealed an increase in the rate of aggression after a management event occurred. The best predictor of aggression in a cage was the type of management event that occurred. Various factors including the number of daily management events, the total time of management events, the technicians involved, reproductive season, and their interactions also showed significant associations with daily aggression levels. Our findings demonstrate that human management events are associated with an increase in conspecific aggression between rhesus macaques and thus have implications regarding how humans manage primates in research facilities.