The Influence of Site Familiarity and Kin Interactions on the Dispersal of a Passerine Bird

Abstract

Dispersal is a fundamental component of life history, but determining the causal factors behind individual dispersal decisions is often difficult. However, it is known that competitive and cooperative interactions can play an important role. Western bluebirds (Sialia mexicana) provide a unique opportunity to investigate the role of kin interactions mediated by aggressive behavior on local dispersal. A long-term dataset on relatedness, natal and breeding location, cavity density, and aggressive behavior was used to test the hypotheses. First-time breeding males dispersed non-randomly and settled closer than expected to their natal nest and father. Because fathers were frequently breeding at the natal nest, distance to both was strongly correlated. However, in cases where fathers did not return to breed, sons settled significantly closer to their natal nest suggesting that fathers may deter sons from settling as close to their natal territory as they would prefer. Although no significant role of aggression has yet to be found, there does appear to be some cooperation between kin over available cavity resources. These results support the importance of natal site familiarity and kin interactions in the local dispersal decisions of western bluebirds, but further studies are necessary to disentangle the relative importance of each.