Effect of Distance on Flap-Bounding Flight Performance

DAVIS, A.P.*; TOBALSKE, B.W.: Effect of Distance on Flap-Bounding Flight Performance

Previous studies suggest that flap-bounding does not offer an aerodynamic advantage to birds flying at slow speeds. Therefore, we hypothesized that a bird using this flight style should quickly accelerate after takeoff and maintain or exceed the minimum aerodynamically attractive speed for its morphology. To test this idea, we studied wing and body kinematics in zebra finch (Taenopygia guttata) as they flew 2, 6, or 10 m within a flight corridor. Flights were recorded using high-speed video (250 Hz), and variation in flap-bounding behavior was measured among and within the flight distances. Average horizontal velocity increased as total flight distance increased. Our results support our hypothesis for flight distances greater than 2 m; flight speeds near 6 m/s were achieved during the middle of 6- and 10-m flights, and 6 m/s has been suggested elsewhere to be the minimum speed that would make flap-bounding aerodynamically attractive for a zebra finch. Wingbeat frequency (WBF) and percent time spent flapping (%FLAP) varied significantly among subsections of 6- and 10-m flights. However, averaging across entire flights, values for these two variables did not change with total flight distance. Compared to performance in a closed-section wind tunnel (at a higher altitude), zebra finch in free flight at 6 m/s exhibit lower %FLAP (50.2 vs. 68.7%) and higher WBF (28.5 vs. 24.3 Hz). These differences may be due to tunnel effects, the non-steady nature of relatively short-distance flight, or variation in air density between study locations. (supported by Murdock #99153)

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