AGE AND SOCIAL CONTEXT INFLUENCE EXPRESSION OF AGGRESSION IN ZEBRA FINCHES

Abstract

By definition, social behaviors are always expressed in the context of other individuals. Because of this, measurements of social behaviors outside the normal social context may not be a reliable measure of typical behavior within it. Moreover, it is difficult to assess the repeatability of social behaviors because, even in the normal social context, behavior may vary with changes in the social context. Here, we assess the importance of social context in the expression of aggression in zebra finches, a social species in which aggression aids in resource acquisition and the maintenance of dominance hierarchies. Aggression was measured repeatedly in a familiar flock and was measured at least once per individual using a mirror test. Birds in a flock were recorded accessing a feeder, and the number and intensity of aggressive interactions, as well as individual dominance rank,were assessed. During the mirror test, aggressive response to the individual’s reflection was scored to assess their reaction to an unfamiliar but equally matched bird. Aggression and dominance were highly repeatable in the flock context and positively correlated with one another. Mirror aggression was not correlated with aggression in the flock for both years of data, suggesting that aggression to familiar versus unfamiliar birds were functionally distinct. Moreover, despite the high repeatability of aggression and dominance, dominance was not stable between years, although males were consistently more dominant in general. Changing social environments leads to unpredictability in the expression of aggression.