Breeding-season sympatry facilitates genetic exchange among allopatric wintering populations of Northern Pintails in Japan and California

The global redistribution of pathogens, such as highly pathogenic avian influenza, has renewed interest in the connectivity of continental populations of birds. Populations of the Northern Pintail (Anas acuta) wintering in Japan and California are considered separate from a management perspective. We used data from band recoveries and population genetics to assess the degree of biological independence of these wintering populations. Distributions of recoveries in Russia of Northern Pintails originally banded during winter in North America overlapped with distributions of Northern Pintails banded during winter in Japan. Thus these allopatric wintering populations are partially sympatric during the breeding season. The primary areas of overlap were along the Chukotka and Kamchatka peninsulas in Russia. Furthermore, band recoveries demonstrated dispersal of individuals between wintering populations both from North America to Japan and vice versa. Genetic analyses of samples from both wintering populations showed little evidence of population differentiation. The combination of banding and genetic markers demonstrates that these two continental populations are linked by low levels of dispersal as well as likely interbreeding in eastern Russia. Although the levels of dispersal are inconsequential for population dynamics, the combination of dispersal and interbreeding represents a viable pathway for exchange of genes, diseases, and/or parasites.