Humming hummingbirds, insect flight tones and a model of animal flight sound.

Why do hummingbirds hum and insects whine when their wings flap in flight? Gutin proposed that a spinning propeller produces tonal sound because the location of the center of aerodynamic pressure on each blade oscillates relative to an external receiver. Animal wings also move, and in addition, aerodynamic force produced by animal wings fluctuates in magnitude and direction over the course of the wingbeat. Here, we modeled animal wing tone as the equal, opposite reaction to aerodynamic forces on the wing, using Lowson's equation for the sound field produced by a moving point force.

Kinematic control of male Allen's hummingbird wing trill over a range of flight speeds.

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.

Strategic Acoustic Control of a Hummingbird Courtship Dive.

Male hummingbirds court females with a high-speed dive in which they "sing" with their tail feathers. The male's choice of trajectory provides him strategic control over acoustic frequency and pressure levels heard by the female. Unlike related species, male Costa's hummingbirds (Calypte costae) choose to place their dives to the side of females.

Resonance frequencies of honeybee () wings.

During flight, insect wings bend and twist under the influence of aerodynamic and inertial forces. We tested whether wing resonance of honeybees () matches the wingbeat frequency, against the 'stiff element' hypothesis that the wing's first longitudinal mode exceeds the wingbeat frequency. Six bees were immobilized with their right wing pair outspread, and stimulated with a shaker while the normal modes were recorded with a scanning Doppler laser vibrometer.

Wing flexibility improves bumblebee flight stability.

Insect wings do not contain intrinsic musculature to change shape, but rather bend and twist passively during flight. Some insect wings feature flexible joints along their veins that contain patches of resilin, a rubber-like protein. Bumblebee wings exhibit a central resilin joint (1m-cu) that has previously been shown to improve vertical force production during hovering flight.

Aerodynamic consequences of wing morphing during emulated take-off and gliding in birds.

Birds morph their wings during a single wingbeat, across flight speeds and among flight modes. Such morphing may allow them to maximize aerodynamic performance, but this assumption remains largely untested. We tested the aerodynamic performance of swept and extended wing postures of 13 raptor species in three families (Accipitridae, Falconidae and Strigidae) using a propeller model to emulate mid-downstroke of flapping during take-off and a wind tunnel to emulate gliding.