Migratory Connectivity of a Songbird: Population Genetics Reveal the Wintering Locations of the American Redstart

Migratory connectivity is a term used to describe how breeding populations are geographically connected to winter populations for a migrating species. Determining the strength of migratory connectivity is important for a number of basic and applied research questions related to the ecology and evolution of migratory species. Population genetics, particularly neutral genetic markers, are often used to measure migratory connectivity for species that are too small to carry transmitters. Previous analyses of genetic variation in the American redstart (Setophaga ruticilla), a Neotropical-Nearctic migrant that breeds in North America and winters in Middle America, revealed unique mitochondrial haplogroups mostly restricted to Newfoundland. I determined the geographic distribution of this population in winter and whether it remains separate or intermixes with other populations of redstarts on the Caribbean winter range. To assess the migratory connectivity of the Newfoundland haplogroup, I sequenced the mitochondrial control region for 180 blood samples collected at nine locations across the non-breeding range. I then compared the sequences to the published sequences from the breeding grounds. I found that the core Newfoundland group (Haplogroup A) was restricted to non-breeding populations in Puerto Rico and the eastern Dominican Republic. Thus, individuals breeding at the north-eastern edge of the range winter almost exclusively in the eastern Caribbean. These results suggest that migratory connectivity in this species occurs over finer geographic scales than previously recognized. These findings contribute to a better understanding of how individuals and populations are connected between breeding and non-breeding improving our understanding of population ecology and evolution.