title: Where in the air? Aerial habitat use of nocturnally migrating birds.
abstract: The lower atmosphere (i.e. aerosphere) is critical habitat for migrant birds. This habitat is vast and little is known about the spatio-temporal patterns of distribution and abundance of migrants in it. Increased human encroachment into the aerosphere makes understanding where and when migratory birds use this airspace a key to reducing human-wildlife conflicts. We use weather surveillance radar to describe large-scale height distributions of nocturnally migrating birds and interpret these distributions as aggregate habitat selection behaviours of individual birds. As such, we detail wind cues that influence selection of flight heights. Using six radars in the eastern USA during the spring (2013-2015) and autumn (2013 and 2014), we found migrants tended to adjust their heights according to favourable wind profit. We found that migrants' flight altitudes correlated most closely with the altitude of maximum wind profit; however, absolute differences in flight heights and height of maximum wind profit were large. Migrants tended to fly slightly higher at inland sites compared with coastal sites during spring, but not during autumn. Migration activity was greater at coastal sites during autumn, but not during spring. This characterization of bird migration represents a critical advance in our understanding of migrant distributions in flight and a new window into habitat selection behaviours.
authors.affiliation: Department of Biology, University of Oklahoma, Norman, OK, USA hortonkg@ou.edu.|Oklahoma Biological Survey, University of Oklahoma, Norman, OK, USA.|Advanced Radar Research Center, University of Oklahoma, Norman, OK, USA.
authors.forename: Kyle G
authors.identifier: 0000-0003-3243-3081
authors.initials: KG
authors.lastname: Horton
authors.affiliation: Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA.
authors.forename: Benjamin M
authors.initials: BM
authors.lastname: Van Doren
authors.affiliation: Advanced Radar Research Center, University of Oklahoma, Norman, OK, USA.|School of Meteorology, University of Oklahoma, Norman, OK, USA.
authors.forename: Phillip M
authors.initials: PM
authors.lastname: Stepanian
authors.affiliation: Cornell Lab of Ornithology, Ithaca, NY, USA.
authors.forename: Andrew
authors.initials: A
authors.lastname: Farnsworth
authors.affiliation: Department of Biology, University of Oklahoma, Norman, OK, USA.|Oklahoma Biological Survey, University of Oklahoma, Norman, OK, USA.
authors.forename: Jeffrey F
authors.initials: JF
authors.lastname: Kelly
mesh_terms: D000531:Altitude; D025041:Animal Migration; D000818:Animals; D001717:Birds / Q000502:physiology*; D017753:Ecosystem; D005426:Flight, Animal; D011825:Radar; D058998:Remote Sensing Technology; D012621:Seasons; D014481:United States; D014919:Wind
keywords: NEXRAD; aeroecology; bird migration; radar; remote sensing