Dynamic soaring is a small-scale flight manoeuvre which is the basis for the extreme flight performance of albatrosses and other large seabirds to travel huge distances in sustained non-flapping flight. As experimental data with sufficient resolution of th ese small-scale movements are not available, knowledge is lacking about dynamic soaring and the physical mechanism of the energy gain of the bird from the wind. With new in-house developments of GPS logging units for recording raw phase observations and of a dedicated mathematical method for postprocessing these measurements, it was possible to determine the small-scale flight manoeuvre with the required high precision. Experimental results from tracking 16 wandering albatrosses (Diomedea exulans) in the southern Indian Ocean show the characteristic pattern of dynamic soaring. This pattern consists of four flight phases comprising a windward climb, an upper curve, a leeward descent and a lower curve, which are continually repeated. It is shown that the primary energy gain from the shear wind is attained in the upper curve where the bird changes the flight direction from windward to leeward. As a result, the upper curve is the characteristic flight phase of dynamic soaring for achieving the energy gain necessary for sustained non-flapping flight.
Conception: G.S. Design: G.S., J.T. and F.B. Execution: J.T. and A.P.N. Interpretation of the findings: G.S. and J.T. Drafting and revising the article: G.S. and J.T.
No competing interests declared.
The authors are grateful to the Institut Polaire Français Paul Emile Victor, which supported this work (IPEV, Program No. 354) – the work was performed according to guidelines established by IPEV and CNRS for the Ethical Treatment of Animals. The authors are also grateful for the support provided by National Science Foundation International Research Fellowship for A.P.N. (no. 0700939).
LIST OF SYMBOLS AND ABBREVIATIONS
- drag coefficient
- lift coefficient
- drag vector
- total energy
- propulsive force due to flapping
- propulsive force
- acceleration due to gravity
- lift vector
- lift vector component in speed vector plane
- lift vector component perpendicular to speed vector plane
- available power
- required power
- wing reference area
- arbitrary time base (1–3)
- current time
- speed at the minimum drag-to-lift ratio, (CD/CL)min
- inertial speed
- speed at minimum power required
- wind speed
- longitudinal coordinate
- lateral coordinate
- wind angle
- air density
- © 2013. Published by The Company of Biologists Ltd