Boundary effects on dispersal between habitat patches by forest birds (Parus major, P-caeruleus)

The behaviour of individuals in response to patch boundaries is a crucial element in many dispersal models. Diffusion- based models of dispersal predict that both the likelihood and direction of dispersal from a habitat patch are influenced by the starting position of a disperser in relation to the patch boundary. An alternative view is that the decision to disperse between patches is uncoupled from movements within the patch of departure. The latter situation is most likely in the case of relatively mobile animals living in small patches with strongly reflecting boundaries. I tested the relationship between proximity to a boundary and natal dispersal in Great and Blue Tits born in relatively small (7- 11 ha) forest patches with high population density in northern Belgium. Birds that were born closer to the forest edge were not more likely to be recruited outside than inside the natal patch. However, Great Tits showed a significant tendency to emigrate in the direction of the nearest patch border. No such effect was found in Blue Tits. A possible explanation is that in Great Tits the direction of dispersal, but not the decision to emigrate, is influenced by a process of familiarization with the area around the natal territory, including areas across the patch border.