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Compensation for wind drift by migrating swifts

Author:
  • Håkan Karlsson
  • Per Henningsson
  • Johan Bäckman
  • Anders Hedenström
  • Thomas Alerstam
Publishing year: 2010
Language: English
Pages: 399-404
Publication/Series: Animal Behaviour
Volume: 80
Issue: 3
Document type: Journal article
Publisher: Elsevier

Abstract english

We investigated the orientation in relation to wind of common swifts, Apus apus, during nocturnal spring and autumn migration. Swifts are highly adapted to a life in the air, showing wind-dependent orientation during nocturnal roosting flights, and may be expected to be more efficient in their wind drift/compensation behaviour than nocturnal passerine migrants, which are usually subjected to full or partial wind drift. A tracking radar at Lund in southern Sweden was used to record the orientation of common swifts (identified by their characteristic radar echo signature) on nocturnal migration flights and to measure wind conditions at the altitudes at which the birds were flying. Comparing track and heading directions under easterly and westerly winds revealed that the swifts shifted their heading distinctly into the wind, with the result that track directions were similar under the different wind conditions. As this pattern of complete compensation for drift from cross-winds occurred during both spring and autumn migration, there were no indications of differences between age classes. In addition, we found an effect of side-winds on equivalent airspeeds, with swifts increasing their airspeed with increasing wind speed. Such a response has been theoretically predicted as part of an optimal behaviour for counteracting wind drift but has hereto not been empirically demonstrated. There was also a positive correlation between overall wind speed and equivalent airspeed, making it difficult to interpret whether the swifts respond to the total wind speed rather than specifically to the side-wind effect. Our results suggest that important differences may exist between species in their capacities to orient in relation to the wind and that the swift may be particularly efficient in adjusting heading direction and airspeed to obtain complete compensation for wind drift during high-altitude nocturnal migratory flights. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Keywords

  • Biological Sciences
  • wind
  • tracking radar
  • side-wind
  • orientation
  • migration
  • drift
  • compensation
  • Apus apus
  • common swift

Other

Published
  • CAnMove
  • ISSN: 1095-8282
Thomas Alerstam
E-mail: thomas [dot] alerstam [at] biol [dot] lu [dot] se

Professor emeritus

Evolutionary ecology

+46 46 222 37 85

E-C225

Sölvegatan 37, Lund

50

Centre for Animal Movement Research
Evolutionary Ecology, Department of Biology
Ecology building S-223 62 Lund Sweden