92.4 Saturday, Jan. 7 Ontogeny of contractile behavior in the flight muscles of birds JACKSON, Brandon E*; TOBALSKE, Bret W; DIAL, Kenneth P; Field Research Station at Fort Missoula, The University of Montana email@example.com
Flight is the defining characteristic of birds yet the mechanisms through which flight ability develops are virtually unknown. Recent efforts focused on pre-flight flapping behaviors (wing assisted incline running and controlled flapping descent) in chukar chicks (Alectoris chukar) have described the ontogenetic progression of morphological, kinematic and aerodynamic characteristics that permit very young (20 days) birds to achieve adult-like aerial locomotor performance. In this study we use these behaviors, which are ubiquitous in developing birds, as a stage to investigate the developmental trajectory of neuromuscular control and function in the pectoralis muscles of precocial chukar and semi-altricial pigeon (Columba livia). 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. Pigeon chicks demonstrate similar trends, including force production that correlates with increasing EMG amplitude, but much later in development (5-8 weeks after hatching) and at larger relative sizes (50-70% adult mass). Muscle performance coincides with the development of external morphology and whole-body locomotor performance in both species. NSF grants IOS-0923606 and IOS-0919799.