CROWDING STRESS AND VIOLENT INJURIES AMONG BEHAVIORALLY INHIBITED RHESUS MACAQUES

Environmental stressors and stable individual differences in human beh avior have both been implicated etiologically in injuries. Because str ess-related injuries are difficult to study experimentally in humans, the authors examined injury incidence in a troop of 21 male and 15 fem ale free-ranging rhesus macaques (Macaca mulatta) before, during, and after a 6-month group confinement. Individual differences in behaviora l inhibition to novelty were assessed, using multiple, quantified obse rvations of behavior by 3 independent raters during 3 previous years. Incidence and severity of medically attended injuries were ascertained from veterinary records over a 2-year study period. A 5-fold increase in the incidence of injuries was documented during confinement stress , and an interaction was found between the stressor and behavioral inh ibition in the prediction of injury incidence. Highly inhibited animal s had significantly higher injury rates during confinement, compared w ith their uninhibited peers, but equal or lower rates in the low stres s periods that preceded and followed confinement. Inhibited individual s appeared to have been specifically targeted for violence during the group stressor but were protected under normative, more predictable co nditions.