Authors: Fengyi Guoa, Jeffrey J. Bulerb, Jaclyn A. Smolinskyb, and David S. Wilcove
Year: 2023
Publication: Proceedings of the National Academy of Sciences
Publication Link: https://www.pnas.org/doi/10.1073/pnas.2203511120
Keywords: bird migration, radar ornithology, stopover hotspot, conservation, migration barrier
Abstract: 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 radar stations to identify
stopover hotspots and assess multiscale habitat associations of migratory landbirds
across the eastern United States during autumn migration. We mapped seasonal
bird densities over 5 y (2015 to 2019) from 60 radar stations covering 63.2 million
hectares. 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 harbored high densities
of migrants for all 5 y, 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. We also found that the prairie
biome in the Midwest (now mostly cropland) 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 multiscale habitat assessments for the conservation of
migratory landbirds.