Hummingbird feather sounds are produced by aeroelastic flutter, not vortex-induced vibration.

TitleHummingbird feather sounds are produced by aeroelastic flutter, not vortex-induced vibration.
Publication TypeJournal Article
Year of Publication2013
AuthorsClark CJ, Elias DO, Prum RO
JournalJ Exp Biol
IssuePt 18
Date Published2013 Sep 15
KeywordsAir Movements, Animal Communication, Animals, Birds, Elasticity, Feathers, Male, Sound, Vibration

Males in the ‘bee’ hummingbird clade produce distinctive, species-specific sounds with fluttering tail feathers during courtship displays. Flutter may be the result of vortex shedding or aeroelastic interactions. We investigated the underlying mechanics of flutter and sound production of a series of different feathers in a wind tunnel. All feathers tested were capable of fluttering at frequencies varying from 0.3 to 10 kHz. At low airspeeds (Uair) feather flutter was highly damped, but at a threshold airspeed (U*) the feathers abruptly entered a limit-cycle vibration and produced sound. Loudness increased with airspeed in most but not all feathers. Reduced frequency of flutter varied by an order of magnitude, and declined with increasing Uair in all feathers. This, along with the presence of strong harmonics, multiple modes of flutter and several other non-linear effects indicates that flutter is not simply a vortex-induced vibration, and that the accompanying sounds are not vortex whistles. Flutter is instead aeroelastic, in which structural (inertial/elastic) properties of the feather interact variably with aerodynamic forces, producing diverse acoustic results.

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Alternate JournalJ. Exp. Biol.
PubMed ID23737562