Comparison of the Behavior of Male Rhesus Macaques in Individual and Group Keeping Conditions: Aggressivity and Anxiety

Individual variability in measures of aggressivity and anxiety in male Rhesus macaques (Macaca mulatta) was studied. The observations addressed 69 males reared in family groups and kept during the study in individual cages and then in outdoor corrals in groups consisting only of males. Measures of observer-directed aggression and anxiety noted in individual conditions were found not to be reliable predictors of measures of aggressivity and anxiety in social group conditions. Categories of males were identified with different reactions to the change in conditions. Transfer of males from individual conditions to corrals had therapeutic effects on their mental status. In corral conditions, pathological forms of self-directed behavior disappeared from the repertoires of most males. Thus, these observations show that keeping conditions can have powerful influences on the behavioral phenotype of adult male Rhesus macaques, which has to be considered when performing studies requiring analysis of aggressivity and anxiety in monkeys.

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