title: Nocturnally migrating songbirds drift when they can and compensate when they must.
abstract: The shortest possible migratory route for birds is not always the best route to travel. Substantial research effort has established that birds in captivity are capable of orienting toward the direction of an intended goal, but efforts to examine how free-living birds use navigational information under conditions that potentially make direct flight toward that goal inefficient have been limited in spatiotemporal scales and in the number of individuals observed because of logistical and technological limitations. Using novel and recently developed techniques for analysis of Doppler polarimetric weather surveillance radar data, we examined two impediments for nocturnally migrating songbirds in eastern North America following shortest-distance routes: crosswinds and oceans. We found that migrants in flight often drifted sideways on crosswinds, but most strongly compensated for drift when near the Atlantic coast. Coastal migrants' tendency to compensate for wind drift also increased through the night, while no strong temporal differences were observed at inland sites. Such behaviors suggest that birds migrate in an adaptive way to conserve energy by assessing while airborne the degree to which they must compensate for wind drift.
authors.affiliation: Department of Biology, University of Oklahoma, Norman, Oklahoma, USA.|Oklahoma Biological Survey, University of Oklahoma, Norman, Oklahoma, USA.|Advanced Radar Research Center, University of Oklahoma, Norman, Oklahoma, USA.
authors.forename: Kyle G
authors.initials: KG
authors.lastname: Horton
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, New York, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Van Doren
authors.affiliation: Advanced Radar Research Center, University of Oklahoma, Norman, Oklahoma, USA.|School of Meteorology, University of Oklahoma, Norman, Oklahoma, USA.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Stepanian
authors.affiliation: Cornell Lab of Ornithology, Ithaca, New York, USA.
authors.forename: Wesley M
authors.initials: WM
authors.lastname: Hochachka
authors.affiliation: Cornell Lab of Ornithology, Ithaca, New York, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Farnsworth
authors.affiliation: Department of Biology, University of Oklahoma, Norman, Oklahoma, USA.|Oklahoma Biological Survey, University of Oklahoma, Norman, Oklahoma, USA.
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Kelly
mesh_terms: D025041:Animal Migration; D000818:Animals; D008962:Models, Theoretical; D058998:Remote Sensing Technology; D012621:Seasons; D020308:Songbirds; D014919:Wind