Meeting Abstract

51.3  Thursday, Jan. 6  Pectoralis contractile activity during WAIR and flight in pigeons JACKSON, Brandon E.*; TOBALSKE, Bret W.; DIAL, Kenneth P.; Univ. of Montana, Missoula brandon.jackson@mso.umt.edu

Wing-assisted incline running (WAIR) in birds combines use of the wings and hindlimbs to ascend obstacles. It is a means of escape in precocial birds before they can to fly, and is used by juvenile and adult birds as an alternative to flight to exploit three-dimensional environments. WAIR is proposed to be an extant biomechanical analogy for the origin of flight as part of the Ontogenetic Transitional Wing hypothesis, wherein proto-birds transitioned from running to flap-running and flapping descents, to level and ascending powered flight. The hypothesis assumes that demands on the flight-muscles incrementally increase from WAIR to descending, level, and ascending flight. To test this assumption, we measured in vivo force (with surgically implanted strain gauges), electromyogram (EMG), and length change (sonomicrometry) in the pectoralis of pigeons (Columba livia, n = 3) as the birds engaged in shallow and steep WAIR (65° and 80°) and in three modes of slow flight: descending at -60°, level, and ascending at 80°. Our results demonstrate that less output is required from the pectoralis during WAIR compared with any mode of flight. Average EMG amplitude, muscle stress, strain, work and power increased in order from 65° WAIR, 80° WAIR, -60° flight, level flight, to 80° flight. Fractional lengthening of the pectoralis was similar among behaviors, but fractional shortening was absent during WAIR such that the pectoralis did not shorten to less than resting length. We conclude that WAIR remains a useful extant model for the evolutionary transition from terrestrial to aerial locomotion in birds, offers incremental adaptive stages, and that WAIR is a less-costly strategy for negotiating 3-D obstacles compared with ascending or vertical flight.