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Flight speeds of swifts (Apus apus): seasonal differences smaller than expected.

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Author

Summary, in English

We have studied the nocturnal flight behaviour of the common swift (Apus apus L.), by the use of a tracking radar. Birds were tracked from Lund University in southern Sweden during spring migration, summer roosting flights and autumn migration. Flight speeds were compared with predictions from flight mechanical and optimal migration theories. During spring, flight speeds were predicted to be higher than during both summer and autumn due to time restriction. In such cases, birds fly at a flight speed that maximizes the overall speed of migration. For summer roosting flights, speeds were predicted to be lower than during both spring and autumn since the predicted flight speed is the minimum power speed that involves the lowest energy consumption per unit time. During autumn, we expected flight speeds to be higher than during summer but lower than during spring since the expected flight speed is the maximum range speed, which involves the lowest energy consumption per unit distance. Flight speeds during spring were indeed higher than during both summer and autumn, which indicates time-selected spring migration. Speeds during autumn migration were very similar to those recorded during summer roosting flights. The general result shows that swifts change their flight speed between different flight behaviours to a smaller extent than expected. Furthermore, the difference between flight speeds during migration and roosting among swifts was found to be less pronounced than previously recorded.

Publishing year

2009

Language

English

Pages

2395-2401

Publication/Series

Royal Society of London. Proceedings B. Biological Sciences

Volume

276

Document type

Journal article

Publisher

Royal Society Publishing

Topic

  • Biological Sciences

Status

Published

Research group

  • Animal Flight Lab

ISBN/ISSN/Other

  • ISSN: 1471-2954