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First published online December 28, 2007
Journal of Experimental Biology 211, 170-179 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.007476
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Contractile properties of the pigeon supracoracoideus during different modes of flight

Bret W. Tobalske1,* and Andrew A. Biewener2

1 Department of Biology, University of Portland, 5000 N. Willamette Boulevard, Portland, OR 97203, USA
2 Concord Field Station, Harvard University, Old Causeway Road, Bedford, MA 01730, USA


Figure 1
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  		Fig. 1. Placement of (A) sonomicrometry crystals for measuring fascicle length in the the supracoracoideus (SUPRA) and the pectoralis (PECT), and (B) strain gauges on the dorsal surface of the deltopectoral crest of the left humerus for measuring bone strain, calibrated to estimate SUPRA and PECT force, in a pigeon (Columbia livia).

 

Figure 2
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  		Fig. 2. (A) Electromyographic (EMG) and contractile activity in the SUPRA and PECT of a pigeon (Columbia livia) engaged in ascending flight (2.7 s); standing on a platform (0–0.4 s), take-off and ascent to a perch (0.4–2.0 s), and landing and resting on the perch (2.0–2.7 s). The shaded area over fourth wingbeat highlights a region analyzed as representing ascending flight. (B) Expanded view of data obtained during an ascending wingbeat, corresponding to the shaded area in A.

 

Figure 3
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  		Fig. 3. Relative timing of length change, activation and force in the SUPRA and PECT of flying pigeons (Columba livia, N=7). Data from different modes of flight were pooled to create this figure. Values are means ± s.d. Broken lines indicate data for a subsequent wingbeat.

 

Figure 4
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  		Fig. 4. Strain gauge recordings from the SUPRA and PECT of a pigeon (Columba livia) illustrating antagonistic force development at the end of downstroke and the end of upstroke. Overlap of force production was apparent even when SUPRA recordings were not corrected for cross-talk from the PECT.

 

Figure 5
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  		Fig. 5. (A) Peak stress ({sigma}m) in the SUPRA and PECT of pigeon (Columba livia) during different modes of flight. (B) Fractional length changes in the SUPRA and PECT according to mode of flight. Resting length is indicated by the origin. Values are means ± s.d., N=7 (except ascending N=6).

 

Figure 6
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  		Fig. 6. Representative work loops from the SUPRA and PECT muscles of a pigeon (Columba livia) engaged in (A,B) level, (C,D) ascending and (E,F) descending flight. Arrows indicate direction of contraction; bold lines indicate EMG activity. The hatched areas feature artificial negative stress ({sigma}m) due to compression of the SUPRA strain gauge by cross-talk from PECT force that remained even after a correction factor was applied; these areas were not included in the analysis.

 

Figure 7
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  		Fig. 7. Mean muscle power output (Pmus) measured in the SUPRA and PECT muscles of the pigeon (Columba livia) during different modes of flight compared with the estimated inertial power requirement (Piner) for upstroke and aerodynamic power requirement (Paero) assuming that all lift is provided during downstroke. Values for Pmus are doubled to represent output from paired left and right muscles. Values are means ± s.d., N=7 (except ascending N=6).

 




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