Meeting Abstract
Flight is the defining characteristic of birds yet the mechanisms through which flight ability develops are virtually unknown. Wing-assisted incline running (WAIR) and controlled flapping descent (CFD) are behaviors that may offer significant adaptive benefits to developing birds and offer an opportunity to measure the development of pectoralis contractile behavior during the ontogenetic transition toward powered flight. In this study we used WAIR and CFD to measure function in the pectoralis muscles of precocial chukar and semi-altricial pigeon. Using indwelling electromyography (EMG), sonomicrometry, and surgically implanted strain gauges to measure muscle force (in the pigeon), we offer the first comparative data on the ontogeny of flight muscle function. Flapping chukar chicks use near-continuous activation at low amplitudes for the first eight days, and progress to stereotypic higher amplitude activation bursts by day 12. The muscle also undergoes increasing strain at higher strain rates with age, and length trajectory becomes more asymmetrical and saw-toothed. At 20-25 days (12-15% adult chukar mass), pectoralis activity and locomotor performance approaches that of adults, although strain rate exhibits a temporary decrease at 61 d.p.h. concurrent with using newly-replaced primary feathers. Pigeon chicks demonstrate similar trends, including force production that correlates with increasing EMG amplitude, but their capacity to use WAIR and CFD occurred much later in development (5-8 weeks after hatching) and at larger relative sizes (50-70% adult mass). Mass-specific power, peak stress, strain, strain rate and work-loop shape factor in juvenile pigeons were all within the range of adult values exhibited during WAIR or descending flight. NSF IOS-0923606 and IOS-0919799.
