DOI: 10.5061/dryad.zs7h44j96
title: Wandering abatross flight data

description: Wandering albatrosses exploit wind shear by dynamic soaring, enabling
 rapid, efficient, long-range flight. To explore this flight mode, we
 compared the ability of a nonlinear dynamic soaring model and a linear
 empirical model to explain observed variation of the airspeeds of
 GPS-tracked albatrosses in across-wind flight. In fast winds (&gt; 8
 m/s), maximum observed airspeeds reach an asymptote at ~ 20 m/s, whereas
 the dynamic soaring model predicts much faster airspeeds, up to around 50
 m/s. We hypothesize that the birds actively limit airspeed by making
 fine-scale adjustments to turn angles and soaring heights. Predicted
 dynamic soaring airspeeds do not extend down to the slowest winds
 (&lt; 3.2 m/s) of observed flight. We hypothesize that in slow winds
 wandering albatrosses obtain additional energy from updrafts over water
 waves. The dynamic soaring model predicts that the minimum wind speed
 necessary to support dynamic soaring at a cruise airspeed of 16 m/s is 3.2
 m/s, achieved via a flight trajectory of linked 137° turns. In reality,
 observed turn angles are typically ~ 60°. Our simulations suggest that
 birds may necessarily use smaller turns angles than the theoretical
 optimum for fast flight in order to limit aerodynamic force on their
 wings.
description: Forty-six wandering albatrosses breeding on Bird Island, South
 Georgia were tracked by GPS during foraging trips made between February to
 September 2004. GPS positions were recorded at intervals of 0.5–2.0 hours.
 In addition, activity loggers recorded saltwater immersion so that time
 actually spent flying could be estimated. We analyzed only direct,
 sustained, bouts of flight and calculated ground velocity between GPS
 locations, resulting in 883 velocity measurements. We
 obtained wind data from the European Center for Medium-Range Weather
 Forecasts (ECMWF) on a grid of approximately 125 km in latitude by 75 km
 in longitude. Wind speed was estimated by interpolation to each bird
 location and reduced to a reference height of 5 m above mean sea level.
 This is the median flight height for albatrosses observed from Bird Island
 and was calculated assuming a logarithmic wind profile and a scale height
 of 0.03. The ground velocity of a bird is the vector
 sum of its average velocity through the air (air velocity) and leeway
 velocity, which is defined as the bird’s advection by the wind in the
 downwind direction. Airspeed, the magnitude of air velocity, was
 calculated by subtracting leeway velocity from ground velocity measured by
 GPS. Leeway velocity was estimated using the slope parameter of a linear
 model of ground speed versus the component of wind velocity in the
 direction of flight <em>W</em>cos(theta), where
 <em>W</em> is the wind speed at a reference height of 5 m and
 theta is the angular difference between wind velocity and ground velocity.
 We calculated leeway velocity as being equal to the slope parameter (0.51)
 times wind velocity (see Supplemental Information for details).
description: We include a data file, a metadata file, and a README file
 grouped together as part of the Wandering albatross flight
 dataset.