Upwash exploitation and downwash avoidance by flap phasing in ibis formation flight
Position and flap phasing between birds in formation flight indicate aerodynamic benefit. Phasing maximizes aerodynamics in bird formations Some bird species have refined their flying skills to the extent that they can fly in near-perfect V, but why they adopt such a tactic has been a matter of conj...
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| Published in: | Nature (London) Vol. 505; no. 7483; pp. 399 - 402 |
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| Main Authors: | , , , , , , , , |
| Format: | Journal Article |
| Language: | English |
| Published: |
London
Nature Publishing Group UK
16-01-2014
Nature Publishing Group |
| Subjects: | |
| Online Access: | Get full text |
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| Summary: | Position and flap phasing between birds in formation flight indicate aerodynamic benefit.
Phasing maximizes aerodynamics in bird formations
Some bird species have refined their flying skills to the extent that they can fly in near-perfect V, but why they adopt such a tactic has been a matter of conjecture. One suggestion is that by flying in a V the birds are able to minimize energy costs, and now an analysis of data captured from free-flying migratory northern bald ibises suggests that there are energetic benefits. The data also reveal a sophisticated and dynamic process of in-flight control. Birds in the V phase their wing-beats to path-match, allowing a trailing bird to exploit the aerodynamic upwash from the bird in front. A bird flying directly behind, however, flaps with opposite phasing in order to minimize the detrimental downwash from the leader's wings. All this must require the birds to have developed a range of phasing strategies to cope with the dynamic wakes produced by flapping wings.
Many species travel in highly organized groups
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. The most quoted function of these configurations is to reduce energy expenditure and enhance locomotor performance of individuals in the assemblage
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. The distinctive V formation of bird flocks has long intrigued researchers and continues to attract both scientific and popular attention
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. The well-held belief is that such aggregations give an energetic benefit for those birds that are flying behind and to one side of another bird through using the regions of upwash generated by the wings of the preceding bird
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, although a definitive account of the aerodynamic implications of these formations has remained elusive. Here we show that individuals of northern bald ibises (
Geronticus eremita
) flying in a V flock position themselves in aerodynamically optimum positions, in that they agree with theoretical aerodynamic predictions. Furthermore, we demonstrate that birds show wingtip path coherence when flying in V positions, flapping spatially in phase and thus enabling upwash capture to be maximized throughout the entire flap cycle. In contrast, when birds fly immediately behind another bird—in a streamwise position—there is no wingtip path coherence; the wing-beats are in spatial anti-phase. This could potentially reduce the adverse effects of downwash for the following bird. These aerodynamic accomplishments were previously not thought possible for birds because of the complex flight dynamics and sensory feedback that would be required to perform such a feat
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. We conclude that the intricate mechanisms involved in V formation flight indicate awareness of the spatial wake structures of nearby flock-mates, and remarkable ability either to sense or predict it. We suggest that birds in V formation have phasing strategies to cope with the dynamic wakes produced by flapping wings. |
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| Bibliography: | ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
| ISSN: | 0028-0836 1476-4687 |
| DOI: | 10.1038/nature12939 |