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First published online September 19, 2006
Journal of Experimental Biology 209, 3887-3897 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02446

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Wing beat kinematics of a nectar-feeding bat, Glossophaga soricina, flying at different flight speeds and Strouhal numbers

Ulla M. Lindhe Norberg^1,* and York Winter²

¹ Department of Zoology, Göteborg University, Box 463, SE-405 30 Göteborg, Sweden
² Department of Biology, Bielefield University, Germany

View larger version (24K): [in a new window]   Fig. 1. Lateral projection of the wing movements relative to the ground of Glossophaga soricina flying from right to left at slow flight speeds, 2.4-3.5 m s-1. The top flight shows the tracks of the wingtip of the bat and the other two flights also include the tracks of the thumb. In slow flight (top flight) the wings are moved backwards relative to the ground during the upstroke. As speed increases the wingtip path becomes more vertical. Wing beat frequency (wb s-1) decreases with increasing flight speed. The times indicated to the left, 0.0055-0.0072 s, are the times between each dot (numbered on the traces). Scale bars, 5 cm.

View larger version (20K): [in a new window]   Fig. 2. Lateral projection of the wing movements relative to the ground of Glossophaga soricina flying from right to left at flight speeds of 4.6-7.5 m s-1. The wingtip paths become more sinusoidal relative to the ground as speed increases. Scale bars, 5 cm. For further explanation, see Fig. 1.

View larger version (35K): [in a new window]   Fig. 3. Ventral projection of the wing-tip movements of Glossophaga soricina flying at 1.7 m s-1. It can be seen that the backward flick of the wingtips is pronounced. The photographs show a hovering bat from below (left) and from the side (right) twisting the wings in the upstroke as in slow flight. T, top position; MD, middle position; B, bottom position of the wings, where the numbers refer to the numbers on the track. The time between each dot (numbered) is 0.0082 s for the two last (left) strokes. Scale bar, 5 cm.

View larger version (25K): [in a new window]   Fig. 4. Ventral projection of the wing movements of Glossophaga soricina flying at 3.15 m s-1. The backward flick of the wingtips is still visible. T, top position; MD, middle position; B, bottom position of the wings. The time between each dot (numbered) is 0.005 s. Scale bar, 5 cm.

View larger version (34K): [in a new window]   Fig. 5. Ventral projection of the wing movements of Glossophaga soricina flying at 3.9 m s-1. There is no backward motion of the wingtips relative to the ground. T, top position; MD, middle position; B, bottom position of the wings. The time between each dot (numbered) is 0.0083 s. Scale bar, 5 cm.

View larger version (29K): [in a new window]   Fig. 6. Lateral projection of the tracks of the wingtip, thumb (at 2.3 and 3.1 m s-1), and tail tip (at 2.3, 3.5 and 4.0 m s-1) relative to the shoulder joint of Glossophaga soricina flying at different flight speeds. The stroke plane angle increases and wing beat frequency decreases with increasing flight speed. The up and down movements of the tail (uropatagium) are most pronounced at the slowest speeds.

View larger version (14K): [in a new window]   Fig. 7. Wing beat frequency plotted on logarithmic coordinates against flight speed in the pregnant specimen of Glossophaga soricina, flying at speeds 1.75-4.78 m s-1 (continuous line) and at speeds 1.75-3.99 m s-1 (broken line).

View larger version (12K): [in a new window]   Fig. 8. Strouhal number as a function of flight speed in Glossophaga soricina. At speeds close to the theoretical minimum power speed (4-6 ms-1) G. soricina operates with a Strouhal number associated with efficient lift and thrust production, 0.17<St<0.22. In the range 3.4-4 ms-1 the Strouhal number is 0.25-0.4, which still is in a favourable region, but when V<3 ms-1 the Strouhal number becomes higher (0.5<St<0.68), indicating that unsteady effects are important and that the production of lift and thrust is unfavourable.

View larger version (12K): [in a new window]   Fig. 9. Strouhal number plotted on logarithmic coordinates against flight speed in Glossophaga soricina.