39.1 Saturday, Jan. 5 Hovering with a high speed wing: How cliff swallows push the envelope of wing shape JACKSON, BE*; HEDRICK, TL; Univ. of North Carolina at Chapel Hill; Univ. of North Carolina at Chapel Hill email@example.com
The energetic demands of flight impose strict constraints on the morphology of flying animals. As a result, functional morphologists often predict tight form-function relationships between wing shape and flight ability, and place wings into shape-performance categories based primarily on fixed-wing aerodynamic theory. For example, swallows possess wings in the high-speed flight category with a narrow and pointed shape predicted to reduce drag while producing sufficient lift at high speeds as the birds chase insects on the wing. Such high-speed performance should come at the cost of reduced force production, and hence limited behaviors, at low speeds. Like most birds however, swallows have a vast array of flight behaviors. Their elaborate elevated mud nests require precise low speed maneuvering and hovering during construction and nestling feeding. How do swallows perform such a diversity of flight behaviors with an apparently single-purpose wing? We filmed cliff swallows (Petrochelidon pyrrhonota) in the field with high speed video while they foraged at speed and while they hovered near nests. Here, we present the first field 3-dimensional kinematic comparison between these extremes of flight in a single species. When hovering, the swallows increased both stroke amplitude (from less than 120° in steady flight to greater than 170° in hovering) and wing beat frequency (from 6-7 Hz to 9.5 Hz). They also use very high geometric angles of attack (>40°) during hovering. Together, these results suggest that wing-shape categories based on fixed-wing theory do not accurately describe the aerodynamic capacity of flapping wings, nor constrain the diversity in flight behaviors within species even in cases where aerodynamic predictions appear to match aspects of flight ecology.