DIAL, K.P; BUNDLE, M.W.; Univ. Montana, Missoula; Univ. Montana, Missoula: Wing-assisted incline running: Accelerometer and force plate data

Birds are capable of orienting aerodynamic forces directed toward a sloped substrate, effectively acting like a spoiler on a race car, to improve traction. During wing-assisted incline running (WAIR), the hind limbs of gallinaceous birds generate the majority of power to raise the bird up steeply sloped obstacles. Accelerometers mounted on the torso (one oriented anteroposteriorly and the other dorsoventrally), of chukar partridge were used to calculate the instantaneous direction and magnitude of whole-body acceleration as birds ascended a variably-pitched inclined runway fitted with a force plate (to measure ground-reaction forces). Results from 127 wing beats in three birds during WAIR upon a 55 degree slope demonstrate that accelerative vectors during the first portion of downstroke are oriented upwards and forward with a mean magnitude of 3.25 g (acceleration of gravity) (+0.11 S.E.). Throughout the last half of downstroke to mid-upstroke, accelerative vectors are directed toward the inclined substrate with a mean magnitude of 3.04 g (+0.14 S.E.). Finally, during mid-to-late upstroke the whole-body accelerations are small (mean=1.63 g, +0.10 S.E.) and are generally directed opposite the direction of travel. These results are discussed in light of the recently proposed WAIR hypothesis that ascribes a novel function to proto-wings, and observed in extant species, delineating intermediate adaptive stages in the origin of avian flight.