Wing kinematics of avian flight across speeds

Abstract

To test whether wing shape affects the kinematics of wing motion during bird flight, we recorded high‐speed video (250 Hz) of four species flying in a variable‐speed wind tunnel. The birds flew at intervals of 2 m s−1, ranging from 1 m s−1 up to their respective maximum flight speed, which varied from 14 to 17 m s−1 depending on the species. Kinematic data obtained from two synchronized, high‐speed video cameras were analyzed using 3D reconstruction. Three species with relatively pointed, high‐aspect ratio wings changed wingbeat styles according to flight speed (budgerigar, Melopsittacus undulatus; cockatiel, Nymphicus hollandicus; ringed turtle dove, Streptopelia risoria). These species used a wing‐tip reversal upstroke, characterized by supination of the distal wing at mid‐upstroke, at equivalent airspeeds ≤7 to 9 m s−1. In faster flight, they used a swept‐wing upstroke, without distal wing supination. At mid‐upstroke at any speed, wingspan in these species was greater than wrist span. In contrast, at all steady flight speeds, the black‐billed magpie Pica hudsonia with relatively broad, low‐aspect ratio wings, used a flexed‐wing, feathered upstroke in which wrist spans were equal to or greater than wingspans. Our results demonstrate that wing kinematics vary gradually as a function of flight speed, and that the patterns of variation are strongly influenced by external wing shape.