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Leading edge vortex in a slow-flying passerine.

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Author

Summary, in English

Most hovering animals, such as insects and hummingbirds, enhance lift by producing leading edge vortices (LEVs) and by using both the downstroke and upstroke for lift production. By contrast, most hovering passerine birds primarily use the downstroke to generate lift. To compensate for the nearly inactive upstroke, weight support during the downstroke needs to be relatively higher in passerines when compared with, e.g. hummingbirds. Here we show, by capturing the airflow around the wing of a freely flying pied flycatcher, that passerines may use LEVs during the downstroke to increase lift. The LEV contributes up to 49 per cent to weight support, which is three times higher than in hummingbirds, suggesting that avian hoverers compensate for the nearly inactive upstroke by generating stronger LEVs. Contrary to other animals, the LEV strength in the flycatcher is lowest near the wing tip, instead of highest. This is correlated with a spanwise reduction of the wing's angle-of-attack, partly owing to upward bending of primary feathers. We suggest that this helps to delay bursting and shedding of the particularly strong LEV in passerines.

Publishing year

2012

Language

English

Pages

554-557

Publication/Series

Biology letters

Volume

8

Issue

4

Document type

Journal article

Publisher

Royal Society Publishing

Topic

  • Biological Sciences

Keywords

  • bird flight
  • leading edge vortex
  • aerodynamics
  • aeroelastics
  • pied flycatcher
  • wind tunnel

Status

Published

Research group

  • Animal Flight Lab

ISBN/ISSN/Other

  • ISSN: 1744-9561