title: Behavioural adaptations to flight into thin air.
abstract: Soaring raptors can fly at high altitudes of up to 9000 m. The behavioural adjustments to high-altitude flights are largely unknown. We studied thermalling flights of Himalayan vultures (Gyps himalayensis) from 50 to 6500 m above sea level, a twofold range of air densities. To create the necessary lift to support the same weight and maintain soaring flight in thin air birds might modify lift coefficient by biophysical changes, such as wing posture and increasing the power expenditure. Alternatively, they can change their flight characteristics. We show that vultures use the latter and increase circle radius by 35% and airspeed by 21% over their flight altitude range. These simple behavioural adjustments enable vultures to move seamlessly during their annual migrations over the Himalaya without increasing energy output for flight at high elevations.
authors.affiliation: Ugyen Wangchuck Institute for Conservation and Environment Research, Bumthang, Bhutan sherub@orn.mpg.de.|Department of Migration and Immuno-Ecology, Max Planck Institute for Ornithology, 78315 Radolfzell, Germany.|Department of Biology, University of Konstanz, 87457 Konstanz, Germany.
authors.forename: Sherub
authors.identifier: http://orcid.org/0000-0002-0143-9395
authors.initials: S
authors.lastname: Sherub
authors.affiliation: Department of Civil, Environmental and Geodetic Engineering, Ohio State University, Columbus, OH 43210, USA.
authors.forename: Gil
authors.identifier: http://orcid.org/0000-0002-9209-9540
authors.initials: G
authors.lastname: Bohrer
authors.affiliation: Department of Migration and Immuno-Ecology, Max Planck Institute for Ornithology, 78315 Radolfzell, Germany.|Department of Biology, University of Konstanz, 87457 Konstanz, Germany.
authors.forename: Martin
authors.identifier: http://orcid.org/0000-0002-9790-7025
authors.initials: M
authors.lastname: Wikelski
authors.affiliation: Department of Migration and Immuno-Ecology, Max Planck Institute for Ornithology, 78315 Radolfzell, Germany.|Department of Biology, University of Konstanz, 87457 Konstanz, Germany.
authors.forename: Rolf
authors.initials: R
authors.lastname: Weinzierl
mesh_terms: D000531:Altitude; D025041:Animal Migration / Q000502:physiology; D000818:Animals; D001631:Bhutan; D001696:Biomechanical Phenomena; D046093:Falconiformes / Q000502:physiology*; D005426:Flight, Animal / Q000502:physiology*; D058998:Remote Sensing Technology
keywords: aerodynamic; movement ecology; non-powered flight; thermalling