During the moult, birds sequentially replace their flight feathers and thus temporarily have gaps in their wings. These gaps will vary in size and position(s) during the course of the moult. We investigated the aerodynamic effects of having moult gaps in a rectangular wing by using a vortex-lattice (panel) approach, and we modelled the effect of moult gap size at the wing moult initiation position, of gap position in the primary tract and of two simultaneous gaps (as occurs during secondary feather moulting in many birds). Both gap size and gap position had a detrimental effect on aerodynamic performance as measured by lift curve slope, effective aspect ratio and the aerodynamic efficiency of the wing. The effect was largest when the moult gap was well inside the wing, because the circulation declines close to the wing tip. In fact, when the gap was at the wing tip, the performance was slightly increased because the lift distribution then became closer to the optimal elliptical distribution. The detrimental effect of moult gaps increased with increasing aspect ratio, which could help to explain why large birds have relatively slow rates of moult associated with small gaps.
JOURNAL ARTICLE|
01 January 1999
On the aerodynamics of moult gaps in birds
A. Hedenström,
A. Hedenström
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Anders.Hedenstrom@zooekol.lu.se.
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S. Sunada
S. Sunada
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Anders.Hedenstrom@zooekol.lu.se.
Search for other works by this author on:
A. Hedenström
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Anders.Hedenstrom@zooekol.lu.se.
S. Sunada
Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK. Anders.Hedenstrom@zooekol.lu.se.
Online Issn: 1477-9145
Print Issn: 0022-0949
© 1999 by Company of Biologists
1999
J Exp Biol (1999) 202 (1): 67–76.
Citation
A. Hedenström, S. Sunada; On the aerodynamics of moult gaps in birds. J Exp Biol 1 January 1999; 202 (1): 67–76. doi: https://doi.org/10.1242/jeb.202.1.67
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