A method to quantify aggressiveness in Japanese quail (Coturnix c. japonica)

Testing procedures which rely on paired fights are unsuitable for measuring individual aggressiveness because the outcome of initial encounters influences subsequent dominance status. In an effort to circumvent this problem, we developed a test system which quantifies aggressiveness in individual Japanese quail by measuring locomotor and pecking activity of test birds presented with the visual stimulus of a conspecific. Using this procedure, we demonstrate that aggression is specific to sexually mature males; however, the intensity of the behavior varies widely among individuals. Scores for each bird are constant with time, reproducible, independent of the gender or behavior of the stimulus bird and accurately predict the outcome of a subsequent paired fight. In addition, we show that fighting per se produces increases and decreases in aggressiveness of dominant and subordinate birds, respectively, and re-orders the rank of a group of birds. This test procedure, therefore, confirms earlier studies which indicate that dominance hierarchies are influenced by initial encounters. Finally, repeat testing is reliable and gives an absolute, not relative, measure of aggressiveness. We conclude that this behavioral test can be applied to future studies addressing the social, developmental and endocrine basis of aggressiveness and dominance in quail and other vertebrates.