DIAL, K.P.: On the Origin and Ontogeny of Bird Flight: Developing Wings Assist Vertical Running

Discussions on the origin of avian flight fall into two philosophical camps: arboreal (tree-down) or cursorial (ground-up) hypotheses, both of which are dominated by paleontological evidence that fails to adequately address logical incremental adaptive stages necessary to achieve fully developed flight mechanics. Here, I present a new model based on novel behavioral and morphological data obtained during post-hatching development of precocial gallinaceous birds. This model offers a solution to the impasse of previous scenarios on the origin of avian flight and differs from the traditional cursorial thesis. Daily progress of locomotor performance (e.g., vertical and horizontal accelerations of flight and terrestrial locomotion) and morphometrics of wing development (e.g., wing loading, feather growth) of three species (Chukar Partridge, n=10; Japanese Quail, n=10; and Ring-necked Pheasant, n=2) from hatching to adult stage were obtained using high-speed video (60-250 Hz) and Doppler radar. To escape being handled, even one-day-old chicks exhibited the following locomotor behavior: they jumped vertically, vigorously beat their featherless forelimbs, and surprisingly swung their hind limbs through an arc similar to that used during over-ground running. Throughout development partially formed wings develop significant aerodynamic forces that assist the legs. This enables birds to “run vertically” achieving substantial heights against rough surfaces such as rocks, cliffs, and tree trunks. This “Assisted Vertical Running Hypothesis” appears consistent with evidence from fossil data and provides incremental adaptive plateaus, as revealed by ontogenetic trajectories, necessary to achieve fully developed avian flight mechanics as observed in living species.