Multi-phase migration models for Nearctic-Neotropical migrant birds can inform conservation planning

Despite recent avian research describing major migratory pathways and stopover regions, many species-specific migratory pathways and stopover locations remain unidentified and uncharacterized. We selected 4 Nearctic-Neotropical migrant bird species experiencing population declines and for which targeted conservation is limited during migratory periods: Cardellina canadensis (Canada Warbler), Setophaga cerulea (Cerulean Warbler), Vermivora chrysoptera (Golden-winged Warbler), and Hylocichla mustelina (Wood Thrush). In three phases, we delineated species-specific migratory pathways with movement tracking data and eBird Status and Trends products (Phase I), identified species-specific stopover landscapes within migratory pathways with eBird Status and Trends products (Phase II), and characterized multi-species stopover hotspots within stopover landscapes with land use/land cover covariates (Phase III). Phase I revealed that 3 species (S. cerulea, V. chrysoptera, and H. mustelina) crossed the Gulf of Mexico via a more easterly pathway during post-breeding migration and a more westerly pathway during pre-breeding migration. In contrast, C. canadensis went around the Gulf of Mexico, while also avoiding the core Prairie Pothole Region and remaining in forested landscapes within the aspen parkland ecotone of southern Canada. In Phase II, forested landscapes predicted to support higher stopover use included major river valleys, the Appalachian Mountains, the northeastern United States, southern Ontario in Canada, and the Central American Highlands. In Phase III, we selected 2 case studies for characterization of predicted stopover habitat use and protected area status. Likely stopover areas near Huntsville, Alabama, USA occurred in deciduous broadleaf forests away from developed land, while in northern Nicaragua near Ocotal, likely stopover areas occurred in premontane and montane tropical forests. Opportunities for conservation action were presented in both case studies, where all stopover use areas contained larger proportions of unprotected land. Moving forward, our flexible three-phase analytical approach provides the tools to support single- and multi-species conservation strategies.