Dial, K.P.; Warrick, D.R.*; Bundle, M.W.: Avian Maneuverability and Stability: Blurred Bodies, Clear Heads

Popular models of avian maneuverability based on steady-state assumptions and parameters such as wing loading fail to describe the full ecological and evolutionary import of maneuvering performance, particularly during low speed, flapping flight. Previous studies revealed that in this key flight regime maneuvering is saltatory, and involves authoritative use of velocity-generated force asymmetries developed during flapping. The effectiveness of this mechanism in maneuvering is largely independent of wing loading; however, low wing loading would result in reduced stability in turbulent conditions. Thus, the quick use of strong aerodynamic forces, as well as the gyroscopic action of flapping wings are likely important factors for maintaining stability, especially for small, lightly wing-loaded birds. Equally important may be a bird’s ability to spare its head from the repeated shocks of saltatory locomotion. Data from x-ray film of magpies in wind tunnels, and light film of pigeons recovering from handler-induced rolls shows that birds isolate their visual and vestibular systems, presumably via cervical reflexes, from the vertical movement and accelerations of the body during flapping flight, and the angular movement and accelerations occurring during rolling maneuvers. Pigeons equipped with neck braces that reduced their head’s normal three-hundred degree range-of-rotation to thirty degrees refused to or could not fly; pigeons with head movement restricted to seventy degrees had difficulty maintaining equilibrium and recovering from handler-induced banks. The neural integration of visual, vestibular, and proprioceptor inputs required for the control of maneuvering and maintenance of straight and level flight has not been extensively studied, although such integration must have been an essential step in the evolution of fully volant species.