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First published online August 31, 2007
Journal of Experimental Biology 210, 3135-3146 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.000273

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Biomechanics of bird flight

Bret W. Tobalske

Department of Biology, University of Portland, 5000 North Willamette Boulevard, Portland, OR 97203, USA

View larger version (28K): [in this window] [in a new window]   Fig. 1. In vivo measurements of mechanical work and power output from the pectoralis, the primary downstroke muscle of the avian wing are accomplished using surgically implanted strain gauges calibrated to measure force from bone strain on the deltopectoral crest of the humerus and using sonimicrometry crystals to measure muscle length (A). Similar methods are employed for the primary upstroke muscle, the supracoracoideus (not shown), which is located deep to the pectoralis (Tobalske and Biewener, in press). (From Hedrick et al., 2003.) (B) A `work loop', the area of which represents in vivo mechanical work in the pectoralis of a cockatiel Nymphicus hollandicus during one wingbeat (adapted from Tobalske et al., 2003). Arrows indicate the progression of contractile behavior. Electromyography (EMG) activity in the pectoralis indicates that the muscle functions to decelerate the wing at the end of upstroke and accelerate the wing during the first third of downstroke.

View larger version (14K): [in this window] [in a new window]   Fig. 2. U-shaped curves of power as a function of flight speed in birds. (A) Estimated mechanical power output required for flight in a European kestrel Falco tinnunculu (from Rayner, 1999). Paero, total aerodynamic power, Pind, induced power, Ppar, parasite power and Ppro, profile power, Vmp, velocity for minimum power, Vmr, velocity for maximum range. (B) In vivo mechanical power output from wind-tunnel flight across flight speeds as measured using strain gauges, sonomicrometry and wing and body kinematics in dove Zenaida macroura, cockatiel Nymphicus hollandicus, magpie Pica hudsonica (from Tobalske et al., 2003). (C) Oxygen consumption, an index of metabolic power output, measured in cockatiels over a range of flight speeds using gas respirometry (from Bundle et al., 2007).

View larger version (22K): [in this window] [in a new window]   Fig. 3. Wing kinematics differ depending upon a bird's wing design and flight speed. (A) Birds with pointed, high-aspect ratio wings such as the pigeon Columba livia transition from tip-reversal upstrokes during slow flight to feathered upstrokes at intermediate speeds and a swept-wing upstroke during fast flight. (B) Birds with rounded, low-aspect ratio wings such as the black-billed magpie Pica hudsonica use a flexed upstroke at all flight speeds. Shown are wingtip (filled circles) and wrist (open circles) paths in dorsal and lateral view (from Tobalske and Dial, 1996).

View larger version (51K): [in this window] [in a new window]   Fig. 4. Representations of vortex wakes shed from the wings of a thrush nightingale Luscinia luscinia at slow (A), medium (B) and fast (C) flight speeds in a wind tunnel, measured using digital particle image velocimetry [DPIV (from Spedding et al., 2003)]. Red and blue indicate the wake from upstroke and downstroke, respectively. Both phases of the wingbeat are aerodynamically active at each speed, and there are prominent cross-stream vortices apparent at the ends of half-strokes during slower flight (A,B) and throughout the wingbeat cycle during faster flight (C).

View larger version (7K): [in this window] [in a new window]   Fig. 5. Intermittent flight postures exhibited by budgerigar Melopsittacus undulatus as a function of flight speed in a wind tunnel. Black, glide; grey, partial bound; white, bound (from Tobalske and Dial, 1994). As flight speed increases, the proportion of non-flapping phases consisting of glides decreases, and the proportion consisting of bounds increases.

View larger version (9K): [in this window] [in a new window]   Fig. 6. Representation of a left turn during slow flight in a pigeon Columba livia, as seen in caudal view (from Warrick and Dial, 1998). (A) Roll is initiated using greater velocity on the outside (right) wing during the first part of downstroke. (B) Roll is arrested using greater velocity on the inside (left) wing during the latter half of downstroke.

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