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First published online November 5, 2004
Journal of Experimental Biology 207, 4255-4268 (2004)
Published by The Company of Biologists 2004
doi: 10.1242/jeb.01283
The relationship between wingbeat kinematics and vortex wake of a thrush nightingale
1 Department of Animal Ecology, Lund University, Ecology Building, SE-223 62
Lund, Sweden
2 Department of Aerospace and Mechanical Engineering, University of Southern
California, Los Angeles, CA 90089-1191, USA
* Author for correspondence (e-mail: m.rosen{at}usc.edu)
Accepted 14 September 2004
The wingbeat kinematics of a thrush nightingale Luscinia luscinia were measured for steady flight in a wind tunnel over a range of flight speeds (5–10 m s–1), and the results are interpreted and discussed in the context of a detailed, previously published, wake analysis of the same bird. Neither the wingbeat frequency nor wingbeat amplitude change significantly over the investigated speed range and consequently dimensionless measures that compare timescales of flapping vs. timescales due to the mean flow vary in direct proportion to the mean flow itself, with no constant or slowly varying intervals. The only significant kinematic variations come from changes in the upstroke timing (downstroke fraction) and the upstroke wing folding (span ratio), consistent with the gradual variations, primarily in the upstroke wake, previously reported.
The relationship between measured wake geometry and wingbeat kinematics can be qualitatively explained by presumed self-induced convection and deformation of the wake between its initial formation and later measurement, and varies in a predictable way with flight speed. Although coarse details of the wake geometry accord well with the kinematic measurements, there is no simple explanation based on these observed kinematics alone that accounts for the measured asymmetries of circulation magnitude in starting and stopping vortex structures. More complex interactions between the wake and wings and/or body are implied.
Key words: wingbeat kinematics, vortex wake, thrush nightingale, Luscinia luscinia, DPVI, aerodynamics, bird flight, bird, wind tunnel
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