Meeting Abstract

105.3  Wednesday, Jan. 7  Wake patterns of the wings and tail of hovering hummingbirds ALTSHULER, Douglas L.*; PRINCEVAC, Marko; PAN, Hansheng; LOZANO, Jesse; University of California, Riverside; University of California, Riverside; University of California, Riverside; University of California, Riverside douga@ucr.edu

The role of bird tails in generating forces, maintaining stability, and enhancing maneuverability has been considered for birds during forward flight. However, aerodynamic contributions of the tail to hovering flight are completely unknown. Here we demonstrate that hovering Anna’s hummingbirds (Calypte anna) use complex tail kinematic patterns ranging from in phase to antiphase movement with the wings, covering several phase shifted patterns. We also employed Particle Image Velocimetry (PIV) to attain detailed flow measurements in the horizontal plane under individual hummingbirds at three levels with respect to the tail: in the tail, at the tail tip, and just below the tail. The velocity patterns underneath the wings indicate that flow oscillates between the forward and backward directions in response to the down- and up-strokes, respectively, and that the sideways flows with respect to the bird are consistently from the periphery to directly underneath the body axis. These results are consistent with a ring vortex pattern corresponding to each stroke. The region around the tail is dominated by axial flows along the body axis and away from the bird. We propose that these flows are generated by interaction between the wakes of the two wings at the end of the upstroke, and that the tail acts as a baffle to generate pitching moments that contribute to pitch stability.