Meeting Abstract

70.4  Wednesday, Jan. 6  3D Skeletal Kinematics During Hovering in Hummingbirds TOBALSKE, B.W.*; ROS, I.G.; HEDRICK, T.L.; WARRICK, D.R.; BIEWENER, A.A.; Univ. of Montana; Harvard Univ.; Univ. of North Carolina, Chapel Hill; Oregon State Univ.; Harvard Univ. bret.tobalske@mso.umt.edu

The ability to sustain hovering in hummingbirds is attributed in part to their highly-derived wing morphology and use of an aerodynamically-active upstroke with supination of the wing. Aerodynamic measurements suggest that the upstroke produces less force than the downstroke, a consequence of wing twist perhaps due to constraints upon supination at the shoulder. Prior kinematic studies suggest that the wing is held “rigid” during the wingbeat cycle, without flexion and extension at the elbow and wrist. To better understand wing function, we measured 3D skeletal and external kinematics during hovering in ruby-throated hummingbirds (Archilocus colubris, N = 4, 3.3 g). We used a pair of fluoroscopes in combination with light cameras sampling at 1000 Hz. We observed significant flexion and extension, pronation and supination at each joint in the wing. Consistent with an early hypothesis from anatomical study, the majority of the movement of the leading edge of the wing could be accounted for by humeral rotation (45%), elevation and sweep (22%). Long axis rotations of 75, 15 and 90 degrees were observed for the humerus, forearm and wrist, respectively. During downstroke, the wing featured relatively little axial twist, and rotations originated predominantly from the humerus and antebrachium. During upstroke, supination increased with distance along the wing and mostly originated from rotation distal to the wrist. Axial twist in the external wing segment from the elbow to the wrist closely matched twist in the antebrachium, but we are unable at present to resolve how much twist beyond the wrist originated from the skeleton or the feathers. Periodicity in kinematic-chain residuals indicated feather bending occurs either due to inertial or aerodynamic loads. NSF Grants: IOS-0923606 & IOS-0744056