TOBALSKE, B.W.; PUCCINELLI, L.A.; Univ. of Portland, Oregon; Univ. of Portland, Oregon: Effects of Flight Mode on Contractile Activity of the Pectoralis in Zebra Finch

Flap-bounding is a widespread form of intermittent flight used by birds including the zebra finch (Taeniopygia guttata). Previous workers have hypothesized that intermittent bounds permit small birds to vary mechanical work and power output to meet different demands during flight while using their major dowstroke muscle, the pectoralis, in a fixed manner. In a test of this hypotheses, we used sonomicrometry and electromyography to measure in vivo length change and neuromuscular recruitment in the pectorals of zebra finch (N = 7) as the birds flew in different modes (ascent, descent, and level). We used high-speed video (250 Hz) to correlate muscle activity with patterns of wing motion. Flight mode had a significant effect (P < 0.05) upon pectoralis strain, strain rate, fractional shortening, the relative timing of electrical activity (onset, offset, and duration), wingbeat frequency, and percent time spent flapping. These patterns do not support the hypothesis that contractile activity is fixed in the pectoralis of small flap-bounding birds. Rather, our results suggest that zebra finch vary work and power output using variable muscle dynamics and intermittent bounds. Between flights with and without surgically implanted transducers and electrodes, zebra finch exhibited significant differences in percent time spent flapping and flight speed. This identifies a potential limitation of in vivo experiments, and similar studies of bird flight should therefore include measurements of the extent to which flight performance is compromised by experimental conditions. (Murdock 2001208)