Kin aggression and resource availability influence phenotype-dependent dispersal in a passerine bird

Understanding the causes of dispersal is important as it strongly influences population dynamics and evolution. However, context dependency of dispersal decisions, such as effects of social interactions and resource availability, is rarely disentangled from intrinsic factors, such as animal personality. Western bluebirds provide a unique opportunity to investigate the relative importance of intrinsic versus extrinsic factors in dispersal decisions because they display distinct aggressive personality types, have high recruitment of sons to the natal population, and depend on nest cavities, a resource that is easy to quantify. Here, we measured territorial interactions among kin and non-kin, resource availability, and aggressive behavior over an 11-year period to determine how they influenced dispersal decisions of male offspring. We found that distance dispersed from kin was driven by a male's own aggression, the aggression of his nearest kin, and the resources available on the natal territory. Both aggressive males and males with aggressive kin dispersed longer distances, as did males who had fewer resources on their natal territories. Thus, dispersal in this species is influenced jointly by intrinsic and extrinsic factors. Because resource acquisition and personality type are interdependent in this species, changes in the social environment are likely to have important consequences for population dynamics.