In the course of a 13-year study of fall migration of Nearctic-breeding landbirds through a site in the Valle Central of Costa Rica, 5,549 migrant birds of 63 species, and 782 local residents of 28 species, were banded. Arrival dates of migrant species were fairly constant from year to year with passage migrants tending to arrive earlier than winter resident species. Differences in numbers and timing of first-year vs. older birds were noted in some species. Passage migrants showed higher fat deposits than did winter resident species and were virtually never recaptured in succeeding years, indicating a lack of fidelity to specific stopover sites. Winter resident species were recaptured in years following banding at frequencies approaching those for many resident species. Among winter resident species, individuals arriving early had higher fat deposits and were recaptured less frequently than those arriving later; apparently the latter were most likely to remain for the winter in or near the study area. This arrangement probably reduces intraspecific competition between transient and resident individuals of these species. Both at regional and local levels, migrant and local resident species differed in size distributions and to some extent in diet; these differences may reduce competition between these groups. Resident species had generally ceased to nest by the time the migrants arrivedin large numbers, but usually were feeding fledglings and/or moulting, suggesting that the presence of the migrants does not result in a scarcity of resources. The long-term but low-intensity, low-budget nature of this study may make it feasible to duplicate in many areas of the Neotropics, where information is needed regarding effects of land-use changes on resident and migrant avifaunas.