Kinematic, aerodynamic and anatomical mechanisms in the slow, maneuvering flight of pigeons

A high-speed (200 Hz) infrared video system was used in a three-dimensional analysis of pigeon wing and body kinematics to determine the aerodynamic and anatomical mechanisms they use to produce force asymmetries to effect a turn during slow (3 m s-1) flight. Contrary to our expectations, pigeons used downstroke velocity asymmetries, rather than angle of attack or surface area asymmetries, to produce the disparities in force needed for directional changes. To produce a bank, a velocity asymmetry is created early in the downstroke and, in the majority of cases, then reversed at the end of the same downstroke, thus arresting the rolling angular momentum. When the velocity asymmetry was not reversed at the end of downstroke, the arresting force asymmetry was produced during upstroke, with velocity asymmetries creating disparate drag forces on the wings. Rather than using subtle aerodynamic variables to produce subtle downstroke force asymmetries, pigeons constantly adjust their position using a series of large alternating and opposing forces during downstroke and upstroke. Thus, a pigeon creates a precise 'average' body position (e.g. bank angle) and flight path by producing a series of rapidly oscillating movements. Although the primary locomotor event (downstroke) is saltatory, maneuvering during slow flight should be considered as a product of nearly continuous, juxtaposed force generation throughout the wingbeat cycle. Further, viewing upstroke as more than stereotypical, symmetrical wing recovery alters the evolutionary and functional context of investigations into the musculoskeletal mechanisms and the associated neural control involved in this unique kinematic event.