Resighting data reveal weak connectivity from wintering to breeding grounds in a range-restricted and endangered long-distance migratory passerine

Understanding migratory connectivity is fundamental to the ecology, evolution, and conservation of migratory species. The endangered Kirtland's Warbler (Setophaga kirtlandii) has a restricted breeding range in early successional jack pine (Pinus banksiana) forests with most of the population in northern Michigan and smaller subpopulations in Wisconsin and Ontario. Kirtland's Warblers spend the winter almost exclusively in the Bahamian Archipelago. Using a combination of visual searches and radiotelemetry, we relocated 89 Kirtland's Warblers on the breeding grounds that were captured and banded on two islands in the central Bahamas. We quantified the strength of migratory connectivity using a new metric "MC," and the Mantel test. We found that regardless of wintering island, Kirtland's Warblers intermixed heavily on the breeding grounds, having migrated to sites throughout the entire breeding range. Our estimates indicated weak connectivity between the wintering and breeding grounds, as might be predicted from a species that uses ephemeral, early successional habitat on both the wintering and breeding grounds. These results suggest that loss of habitat at a wintering site would have a diffuse effect across the entire population. The importance of a landscape approach to conservation of this species, long recognized in the breeding season and more recently emphasized on the wintering grounds, is supported by our findings