Intrinsic Markers Reveal Breeding Origin and Geographically-Structured Migration Timing of Two Songbird Species at a Coastal Stopover Site

Abstract We used stable hydrogen isotope markers to identify geographic provenance of Blackpoll Warblers (Setophaga striata) and Red-eyed Vireos (Vireo olivaceus) passing through a coastal stopover area in the Gulf of Maine on fall migration, and supplemented δ2 H signatures from feathers with wing length data as an additional proxy for migration origin, since geographic size variation has been documented for this species. We captured migrant blackpolls with putative origins from as close as the Adirondacks, New Brunswick, and northwestern Maine, and potentially as far as Alaska. We captured vireos with putative origins from as close as Maine and Nova Scotia, and potentially as far as British Columbia and Alberta. We found a significant relationship between blackpoll wing length and capture date indicating that birds with longer wings– and thus likely from more western and northern breeding regions – passed through the capture site earlier in the season than more local breeders. In contrast, vireos from more distant breeding latitudes passed through the capture site later in the season. These results demonstrate that mid-coast Maine serves as a catchment area for both Blackpoll Warblers, and Red-eyed Vireos, and provides some evidence that connectivity between breeding areas and stopover sites may be strong for blackpolls; however, additional study linking breeding and stopover sites across the migratory range of both species is necessary to understand more fully how strong connectivity is between breeding and stopover areas for these species.