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Revising the wintering distribution and habitat use of the Kirtland’s warbler using playback surveys, citizen scientists, and geolocators

Understanding the population dynamics of migratory animals throughout the full annual cycle is critical for effective conservation, and requires knowing where populations are located throughout the year. For most Neotropical−Nearctic migratory bird species, breeding distributions are well-described, but less is generally known about their migratory paths, stopover areas, and wintering grounds. The Kirtland’s warbler Setophaga kirtlandii is an endangered longdistance migratory passerine with a restricted but well-described breeding distribution located primarily in Michigan (USA), with small subpopulations in Wisconsin (USA) and Ontario (Canada). Kirtland’s warbler migratory paths and the location of important stopover areas were re cently estimated, but published accounts of their wintering distribution and winter habitat use are currently incomplete and conflicting. In this paper, we used 128 detections from playback surveys, 86 sightings from birders entered into eBird, and previously published light-level geolocator tracking data from 27 males to refine the distribution and habitat use of wintering Kirtland’s warblers. We demonstrate that Kirtland’s warblers are most abundant in the central Bahamas, but also winter elsewhere in The Bahamas, Turks and Caicos, Cuba, and possibly southern Florida and Bermuda. Despite some previous accounts, which suggest that Kirtland’s warblers primarily winter in Caribbean pine habitat, our survey and eBird data indicate that they almost exclusively use a variety of broadleaf scrub habitats. This new information will help guide future research and conservation efforts designed to protect this endangered species.