Aerial Righting, Directed Aerial Descent, and Maneuvering in the Evolution of Flight in Birds
This thesis consists of four major studies: a study of incipient flight behaviors in young birds over ontogeny (chapter 1); a detailed study of maneuvering using physical models of a likely ancestral bird morphology (chapter 2); a comparative study of maneuvering ability in several stem-group birds, within a phylogenetic context (chapter 3); and development of basic engineering theory to quantify the turbulence sensitivity of shapes to environmental turbulence of given scales and spectral content. The studies have identified: 1) shifts in function from asymmetric to symmetric movements in young birds, contrary to predictions from alternative hypotheses and occurring before wing-assisted incline running; 2) shifts in function, tied to angle of attack, of asymmetric appendage postures in creating yawing and rolling moments; and 3) migration of control effectiveness as tails are shortened and other features change, during the early evolution of birds. The work plugs some considerable gaps in current prevailing theories (e.g. Dial, 2003; Tobalske et al., 2011) and provides a test of hypotheses of flight evolution not based in outdated "trees-down'' or "ground-up'' paradigms from the past, but rather based on the universal need of airborne animals to maneuver (Dudley and Yanoviak, 2011; Maynard-Smith, 1953).
This work seeks to understand early flight evolution from a maneuvering perspective; every animal in the air must maneuver, and by understanding "powered'' flight as simply a point along a spectrum of maneuvering flight (Dudley and Yanoviak, 2011), unifying breakthroughs are made. It is hoped that the multifaceted approach taken here, with ontogenetic series, aerodynamic studies, and phylogenetic approaches, is robust against the shortcomings of any one approach individually: confounding ontogeny with evolution (as may be the case in others' studies of alternative hypotheses, e.g. Dial, 2003); inferring implausible functions from paleontological material in the absence of proper benchmarking against live animals; or misdiagnosis of how forms work in the absence of functional studies.