Department of Evolution, Ecology and Organismal Biology, University of California Riverside, CA 92521, USA
Department of Evolution, Ecology and Organismal Biology, University of California Riverside, CA 92521, USA.
J Exp Biol. 2018 Jul 23;221(Pt 14):jeb173625. doi: 10.1242/jeb.173625.
Wing trills are pulsed sounds produced by modified wing feathers at one or more specific points in time during a wingbeat. Male Allen's hummingbirds () produce a sexually dimorphic 9 kHz wing trill in flight. Here, we investigated the kinematic basis for trill production. The wingtip velocity hypothesis posits that trill production is modulated by the airspeed of the wingtip at some point during the wingbeat, whereas the wing rotation hypothesis posits that trill production is instead modulated by wing rotation kinematics. To test these hypotheses, we flew six male Allen's hummingbirds in an open-jet wind tunnel at flight speeds of 0, 3, 6, 9, 12 and 14 m s, and recorded their flight with two 'acoustic cameras' placed below and behind, or below and lateral to the flying bird. The acoustic cameras are phased arrays of 40 microphones that used beamforming to spatially locate sound sources within a camera image. Trill sound pressure level (SPL) exhibited a U-shaped relationship with flight speed in all three camera positions. SPL was greatest perpendicular to the stroke plane. Acoustic camera videos suggest that the trill is produced during supination. The trill was up to 20 dB louder during maneuvers than it was during steady-state flight in the wind tunnel, across all airspeeds tested. These data provide partial support for the wing rotation hypothesis. Altered wing rotation kinematics could allow male Allen's hummingbirds to modulate trill production in social contexts such as courtship displays.
翼颤音是在翅膀挥动过程中的一个或多个特定时间点，由经过修饰的翼羽产生的脉冲声。雄性艾伦氏吸蜜鸟（Allen's hummingbird）在飞行中产生具有性二态性的 9 kHz 翼颤音。在这里，我们研究了产生颤音的运动学基础。翼尖速度假说认为，在翅膀挥动过程中的某个时间点，翼尖的空速调制了颤音的产生，而翼旋转假说则认为，颤音的产生是由翼旋转运动学调制的。为了检验这些假说，我们在飞行速度为 0、3、6、9、12 和 14 m/s 的开放式射流风洞中飞行了六只雄性艾伦氏吸蜜鸟，并使用放置在鸟下方和后方或下方和侧面的两个“声学相机”记录它们的飞行。声学相机是由 40 个麦克风组成的相控阵，使用波束形成技术在相机图像内定位声源。在所有三个相机位置，颤音声压级（SPL）与飞行速度呈 U 形关系。SPL 在垂直于划水平面时最大。声学相机视频表明，在旋后期间产生了颤音。与在风洞中进行的稳定状态飞行相比，在所有测试的空速下，颤音在机动过程中的声音高达 20 dB。这些数据为翼旋转假说提供了部分支持。翼旋转运动学的改变可以使雄性艾伦氏吸蜜鸟在求偶表演等社交情境中调节颤音的产生。
