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First published online October 7, 2004
Journal of Experimental Biology 207, 3977-3984 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01235

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The energetic cost of variations in wing span and wing asymmetry in the zebra finch Taeniopygia guttata

C. Hambly^1,*, E. J. Harper² and J. R. Speakman^1,3

¹ Aberdeen Centre for Energy Regulation and Obesity, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, Scotland, UK
² The Waltham Centre for Pet Nutrition, Waltham-on-the-Wolds, Leicestershire, LE14 4RT, England, UK
³ Aberdeen Centre for Energy Regulation and Obesity, Division of Energy Balance and Obesity, Rowett Research Institute, Bucksburn, Aberdeen AB21 9BS, Scotland, UK

^* Author for correspondence (e-mail: c.hambly{at}rowett.ac.uk)

Accepted 10 August 2004

Asymmetry is a difference in the sizes of bilaterally paired structures. Wing asymmetry may have an effect on the kinematics of flight, with knock-on effects for the energetic cost of flying. In this study the ¹³C-labelled bicarbonate technique was used to measure the energy expended during the flight of zebra finches Taeniopygia guttata, prior to and after experimental manipulation to generate asymmetry and a change in wing span by trimming the primary feathers. In addition, simultaneous high-speed video footage enabled differences in flight kinematics such as flight speed, wing amplitude, up- and downstroke duration and wing beat frequency to be examined. In 10 individuals, the primary feathers on the right wing were trimmed first, by 0.5 cm, and then by an additional 0.5 cm in six of these individuals. In a separate `control' group (N=7), approximately 0.25 cm was trimmed off the primary feathers of both wings, to produce the same reduction in wing span as 0.5 cm trimmed from one wing, while maintaining symmetry. When birds were manipulated to become asymmetric they maintained flight speed. They also increased the left wing amplitude and decreased the right up- and downstroke durations to counteract the changes in wing shape, which meant that they had an increase in wing beat frequency. When the wing area was reduced while maintaining symmetry, birds flew with slower flight speed. In this case wing amplitude did not change and wing upstroke slightly decreased, causing an increased wing beat frequency. The mean flight cost in the pre-manipulated birds was 1.90±0.1 W. There was a slight increase in flight cost with both of the asymmetry manipulations (0.5 cm, increase of 0.04 W; 1.0 cm, increase of 0.12 W), neither of which reached statistical significance. There was, however, a significantly increased flight cost when the wing span was reduced without causing asymmetry (increase of 0.45 W; paired t-test T=2.3, P=0.03).

Key words: flight cost, wing asymmetry, labelled bicarbonate technique, zebra finch, Taeniopygia guttata, kinematics