THE EFFECTS OF CAR TRAFFIC ON BREEDING BIRD POPULATIONS IN WOODLAND .2. BREEDING DISPERSAL OF MALE WILLOW WARBLERS (PHYLLOSCOPUS-TROCHILUS) IN RELATION TO THE PROXIMITY OF A HIGHWAY

1. In this study the dispersal activity of male willow warblers Phylloscopus trochilus breeding next to a highway carrying heavy traffic was investigated. 2. Breeding dispersal distances of yearling males along the road were larger than at further distances and were in the same order of magnitude as natal dispersal distances (medians being 303 and 515 m, respectively). 3. A simulation of dispersal directions, adjusted for actual landscape features, indicated that breeding dispersal was actively directed away from the road. 4. There appeared to be a relation between dispersal and breeding performance for yearling males, unsuccessful males moving more frequently and further (median 294 m) than successful males (median 120 m). 5. At the individual level, the increased dispersal activity of yearlings close to the highway constitutes an 'escape' mechanism from low quality areas. At the population level it possibly stabilizes source populations. Dispersal characteristics should be incorporated into spatial population models.