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Assessing the aerodynamic effects of tail elongations in the house martin (Delichon urbica): implications for the initial selection pressures in hirundines
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posted on 2000-10-01, 00:00 authored by K J Park, M R Evans, Kate BuchananKate BuchananOf the three species of hirundine that breed sympatrically across the U.K., one, the barn swallow, has outer tail feathers elongated into streamers, whereas the other two species, the house martin and the sand martin, do not. The tail streamer of the barn swallow is regarded as a classic example of a sexually selected trait. Recent evidence, however, has suggested that streamers may have evolved largely through natural selection for enhanced flight performance and increased maneuverability. We tested the hypotheses that small streamers (1) increase performance in turning flight, but (2) decrease performance in flight variables related to velocity. We manipulated the lengths of house martin outer tail feathers and measured changes in their free-flight performance, using stereo-video to reconstruct the birds' three-dimensional flight paths. Five flight variables were found to best describe individual variation in flight performance. Of these five, the three variables determining maneuverability predicted that flight performance would be optimized by a 6- to 10-mm increase in the length of the outer tail feathers. In contrast, for mean velocity and mean acceleration, extension of the outer tail feathers appears to have a detrimental effect on flight performance. We suggest that the initial selection pressure for streamers in ancestral short-tailed 'barn swallows' was via natural selection for increased maneuverability. In addition, we propose that the benefits of increased maneuverability have differed between hirundines in the past, such that the cost of increasing the length of the outer tail feather has, to date, outweighed the benefits of doing so in streamerless hirundines.
History
Journal
Behavioral ecology and sociobiologyVolume
48Issue
5Pagination
364 - 372Publisher
SpringerLocation
Berlin, GermanyPublisher DOI
ISSN
0340-5443Language
engPublication classification
C1.1 Refereed article in a scholarly journalCopyright notice
2000, Springer-VerlagUsage metrics
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