PATTERNS OF NATAL AND BREEDING DISPERSAL IN BIRDS

1. Dispersal is of critical ecological and evolutionary importance for several issues of population biology, particularly population synchro ny, colonization and range expansion, metapopulation and source-sink d ynamics, and population genetic structure, but it has not previously b een possible to compare dispersal patterns across a wide range of spec ies or to study movement outside the confines of local study areas. 2. Using resampling methods, we verified that statistically unbiased est imates of average dispersal distance and of intraspecific variance in dispersal distance could be extracted from the bird ringing data of th e British Trust for Ornithology. 3. Using data on 75 terrestrial bird species, we tested whether natal and breeding dispersal were influence d by a species' habitat requirements, diet, geographical range, abunda nce, morphology, social system, life history or migratory status. We u sed allometric techniques to ascertain whether these relationships wer e independent of body size, and used the method of phylogenetically in dependent contrasts to ascertain whether they were independent of phyl ogeny. 4. Both natal and breeding dispersal distances were lower among abundant species and among species with large geographical ranges. Di spersal distances and life-history variables were correlated independe nt of phylogeny, but these relationships did not persist after control ling for body size. All morphometrical variables (wing length, tarsus length and bill length) were not significantly correlated with dispers al distances after correcting for body size or phylogenetic relatednes s. 5. Migrant species disperse further than resident ones, this relati on was independent of body size but not of phylogeny. A significant po sitive relation was observed between breeding dispersal distance and l ong-term population decline among migrants, but not among residents. 6 . The species living in wet habitats disperse further than those livin g in dry habitats, which could be explained by the greater patchiness of wet habitats in space and/or time. This relationship was observed o nly for breeding dispersal, suggesting that this habitat variable does not impose the same constraint on natal dispersal.