FIGURE 1. Locomotor development during ontogeny in the chukar partridge from hatching to adulthood.
From the following article:
A fundamental avian wing-stroke provides a new perspective on the evolution of flight
Kenneth P. Dial, Brandon E. Jackson & Paolo Segre
Nature 451, 985-989(21 February 2008)
doi:10.1038/nature06517
Our data suggest a default or basal wing-stroke is used by young and adults and may exist in all birds (Supplementary Videos). The fundamental wing-stroke described herein is used days after hatching and during all ages and over multiple behaviours (that is, flap-running, descending and level flight) and is the foundation of our new ontogenetic-transitional wing hypothesis. At hatching, chicks can ascend inclines as steep as 60° by crawling on all four limbs. From day 8 through adulthood, birds use a consistently orientated stroke-plane angle over all substrate inclines during wing-assisted incline running (red arcs) as well as during descending and level flight (blue arcs). Estimated force orientations from this conserved wing-stroke are limited to a narrow wedge (see Fig. 3b).
