Meeting Abstract
Hummingbirds are famous for the hum of their wings in flight. In addition, males of some species produce a high-frequency sound, the wing trill, with modified wingtip feathers. As the kinematic basis for these sounds is unclear, we sought to characterize how these sounds vary over a range of flight speeds. We flew male Allen’s hummingbirds in our new acoustic wind tunnel, which is a blower-style tunnel with an open working section that makes placing microphones outside of the flow feasible. We filmed them with two high-speed cameras and two “acoustic cameras”, a device that spatially maps sound sources onto a camera image. We tested (1) whether trill amplitude varies with airspeed of the wingtip, and so becomes louder at higher flight speeds; and (2) how the orientation of the sound field varies with speed, given that the change in orientation of the flight stroke from near horizontal (hovering flight) to near vertical (fast forward flight). Our results have implications for how these sounds may be used in communication.
