Halting the global decline of migratory birds requires a better understanding of migration ecology. Stopover sites are a crucial yet understudied aspect of bird conservation, mostly due to challenges associated with understanding broad-scale patterns of transient habitat use. Here we use a national network of weather radars to identify stopover hotspots and assess multi-scale habitat associations of migratory landbirds across the eastern U.S. during autumn migration. We mapped seasonal bird densities over five years (2015 – 2019) from 60 radar stations covering 63.2 million hectares.
Results/Conclusions
At a coarse scale, we found that landbirds migrate across a broad-front with small differences in migrant density between radar domains. However, relatively more birds concentrate along the Mississippi River and Appalachian Mountains. At a finer scale, we identified radar pixels that consistently harbor high densities of migrants for all five years, which we classify as stopover hotspots. Hotspot probability increased with percent cover of all forest types, and decreased with percent cover of pasture and cultivated crops. Moreover, we found strong concentrating effects of deciduous forest patches within deforested regions to contain hotspots. We also found that the prairie biome in the Midwest is likely a migration barrier, with large concentrations of migrants at the prairie-forest boundary after crossing the agricultural Midwest. Overall, the broad-front migration pattern highlights the importance of locally-based conservation efforts to protect stopover habitats. Such efforts should target forests, especially deciduous forests in highly altered landscapes. These findings demonstrate the value of multi-scale habitat assessments for conservation of migratory landbirds.
