title: Flight responses by a migratory soaring raptor to changing meteorological conditions.
abstract: Soaring birds that undertake long-distance migration should develop strategies to minimize the energetic costs of endurance flight. This is relevant because condition upon completion of migration has direct consequences for fecundity, fitness and thus, demography. Therefore, strong evolutionary pressures are expected for energy minimization tactics linked to weather and topography. Importantly, the minute-by-minute mechanisms birds use to subsidize migration in variable weather are largely unknown, in large part because of the technological limitations in studying detailed long-distance bird flight. Here, we show golden eagle (Aquila chrysaetos) migratory response to changing meteorological conditions as monitored by high-resolution telemetry. In contrast to expectations, responses to meteorological variability were stereotyped across the 10 individuals studied. Eagles reacted to increased wind speed by using more orographic lift and less thermal lift. Concomitantly, as use of thermals decreased, variation in flight speed and altitude also decreased. These results demonstrate how soaring migrant birds can minimize energetic expenditures, they show the context for avian decisions and choices of specific instantaneous flight mechanisms and they have important implications for design of bird-friendly wind energy.
authors.affiliation: Cellular Tracking Technologies, LLC, Somerset, PA, USA. mlanzone@gmail.com
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Lanzone
authors.forename: Tricia A
authors.initials: TA
authors.lastname: Miller
authors.forename: Philip
authors.initials: P
authors.lastname: Turk
authors.forename: David
authors.initials: D
authors.lastname: Brandes
authors.forename: Casey
authors.initials: C
authors.lastname: Halverson
authors.forename: Charles
authors.initials: C
authors.lastname: Maisonneuve
authors.forename: Junior
authors.initials: J
authors.lastname: Tremblay
authors.forename: Jeff
authors.initials: J
authors.lastname: Cooper
authors.forename: Kieran
authors.initials: K
authors.lastname: O'Malley
authors.forename: Robert P
authors.initials: RP
authors.lastname: Brooks
authors.forename: Todd
authors.initials: T
authors.lastname: Katzner
mesh_terms: D000531:Altitude; D025041:Animal Migration; D000818:Animals; D005075:Biological Evolution; D020307:Eagles / Q000502:physiology*; D004463:Ecology / Q000379:methods; D005426:Flight, Animal; D010414:Pennsylvania; D020304:Raptors / Q000502:physiology*; D013686:Telemetry / Q000379:methods; D014887:Weather; D014919:Wind