NATAL DISPERSAL AND POPULATION STRUCTURE IN A MIGRATORY SONGBIRD,THE INDIGO BUNTING

Male and female indigo buntings (Passerina cyanea) were equally likely to return and breed in their natal areas. The distances and number of territories between natal and breeding sites were similar between the sexes. The breeding site was not limited by prior occupation of sites by breeding adults closer to the natal territory. Dispersal distances were independent of whether parents or siblings of either sex returned in the same year. Variation in distance within the natal area appeared to be independent of local population density, social competition, active kin recognition, and avoidance of incest, but was affected by date of birth. The local distribution of dispersal distances approximated a neutral model with a decreasing probability of settling with distance from the natal site. A population inbreeding coefficient ΔF of 0.01 was estimated from known genealogies and matings. The proportion of nestlings recaptured in a later year on their natal area was 1.65% of 1,212 nestlings at the George Reserve and 8.78% of 1,332 nestlings at Niles. Locally born birds comprised 1.6% and 13.0% of the breeding population in areas of 10 and 4 km². Evidently most buntings settle and breed more than 2 km from their natal site. The results are inconsistent with predictions of social and avoidance-of-inbreeding hypotheses that are based on the local natal demographic environment. The results are consistent with a model of neutral dispersal within a genetically open population.