Behavioral responses to an unfamiliar intruder were recorded in adolescent/adult rhesus macaques (N = 113). “Intruder” animals were selected based on the age and sex of the test subjects, such that adult animals (7.5 ± 1.6 years of age) were exposed to an unfamiliar adult of the same sex, and subadults (3.3 ± 1 years of age) were exposed to subadult animals of the same sex. Intruders were also selected to match the size of the test subjects as closely as possible. All intruder animals were completely unfamiliar to the test subjects. Prior to the intruder challenge test, the intruder animal was placed into an individual transfer cage, measuring 0.76 m wide × 0.63 m deep × 0.91 m high, for a 30-minute acclimation period. All subjects were tested three at a time in the home-run. For the test, three randomly grouped animals were locked into the outdoor portion of their home run, an enclosure measuring 2.64 m wide × 3 m long × 2.44 m high. After ten minutes, the intruder animal’s cage was placed directly at the front
