Resonating feathers produce courtship song

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SUMMARYFeathers can produce sound by fluttering in airflow. This flutter is hypothesized to be aeroelastic, arising from the coupling of aerodynamic forces to one or more of the feather's intrinsic structural resonance frequencies. We investigated how mode of flutter varied among a sample of hummingbird tail feathers tested in a wind tunnel. Feather vibration was measured directly at 100 points across the surface of the feather with a scanning laser Doppler vibrometer (SLDV), as a function of airspeed, U air . Most feathers exhibited multiple discrete modes of flutter, which we classified into types including tip, trailing vane and torsional modes. Vibratory behavior within a given mode was usually stable, but changes in independent variables such as airspeed or orientation sometimes caused feathers to abruptly 'jump' from one mode to another. We measured structural resonance frequencies and mode shapes directly by measuring the free response of 64 feathers stimulated with a shaker and recorded with the SLDV. As predicted by the aeroelastic flutter hypothesis, the mode shape (spatial distribution) of flutter corresponded to a bending or torsional structural resonance frequency of the feather. However, the match between structural resonance mode and flutter mode was better for tip or torsional mode shapes, and poorer for trailing vane modes. Often, the 3rd bending structural harmonic matched the expressed mode of flutter, rather than the fundamental. We conclude that flutter occurs when airflow excites one or more structural resonance frequencies of a feather, most akin to a vibrating violin string. (SLDV). This device shines a coherent laser on the surface of the feather and uses the Doppler shift of reflected light to calculate the instantaneous velocity in the direction parallel to the laser, across a series of points. SLDV does not require a reflectent to be applied to the surface, unlike regular LDV (Bostwick et al., 2010), allowing its use on objects as small as hummingbird feathers. We measured the feathers in the wind tunnel (see Clark et al., 2013), and also measured the resonance characteristics of a series of feathers stimulated across a range of frequencies by a shaker, an experimental paradigm in which the operating deflection shape approximates the normal modes. We also describe a related aspect of flutter with evolutionary significance: feathers may exhibit a dozen or more modes of flutter, and can abruptly switch or 'jump' from one mode of flutter to another. MATERIALS AND METHODSThe wind tunnel, general methods and definitions for this experiment are as described in the companion paper (Clark et al., 2013). The feathers tested were from wild adult males of 14 species of 'bee' hummingbird (McGuire et al., 2009), obtained in the course of our fieldwork on each of these species under the relevant collecting and import permits. The exact feathers used and the species from which they were obtained are tabulated in the supplementary online material of our previous publications (Clark et al., 2011a;Cla...

Section: Implications For Behaviormentioning

confidence: 99%

mentioning

confidence: 99%

Structural resonance and mode of flutter of hummingbird tail feathers

Clark

Elias

Girard

et al. 2013

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“…Together, these passive mechanisms of tonal and atonal sound production make flight an inherently noisy mode of locomotion, suggesting that feather sonations could evolve easily and repeatedly among birds (Clark and Prum, 2015). The ways in which aeroelastically fluttering feathers have been evolutionarily co-opted for communication have been thoroughly described in two taxa -manakins (Bostwick and Prum, 2003;Bostwick et al, 2010;Prum, 1994Prum, , 1998 and hummingbirds (Clark, 2008;Clark and Feo, 2010;Clark et al, 2011;Hunter, 2008) -and are hypothesized to have evolved at least 27 times in at least nine orders of birds (Clark and Prum, 2015).…”

Section: Introductionmentioning

confidence: 99%

Specialized primary feathers produce tonal sounds during flight in rock pigeons (Columba livia)

Niese

Tobalske

2016

For centuries, naturalists have suggested that the tonal elements of pigeon wing sounds may be sonations (non-vocal acoustic signals) of alarm. However, spurious tonal sounds may be produced passively as a result of aeroelastic flutter in the flight feathers of almost all birds. Using mechanistic criteria emerging from recent work on sonations, we sought to: (1) identify characteristics of rock pigeon flight feathers that might be adapted for sound production rather than flight, and (2) provide evidence that this morphology is necessary for in vivo sound production and is sufficient to replicate in vivo sounds. Pigeons produce tonal sounds (700±50 Hz) during the latter two-thirds of each downstroke during take-off. These tones are produced when a small region of long, curved barbs on the inner vane of the outermost primary feather (P10) aeroelastically flutters. Tones were silenced in live birds when we experimentally increased the stiffness of this region to prevent flutter. Isolated P10 feathers were sufficient to reproduce in vivo sounds when spun at the peak angular velocity of downstroke (53.9-60.3 rad s ), but did not produce tones at average downstroke velocity (31.8 rad s −1 ), whereas P9 and P1 feathers never produced tones. P10 feathers had significantly lower coefficients of resultant aerodynamic force (C R ) when spun at peak angular velocity than at average angular velocity, revealing that production of tonal sounds incurs an aerodynamic cost. P9 and P1 feathers did not show this difference in C R . These mechanistic results suggest that the tonal sounds produced by P10 feathers are not incidental and may function in communication.

“…Non-vocal sound production is widespread throughout the animal kingdom and, in birds, the behavioral mechanisms producing sonations are diverse (e.g. Prum, 2003, 2005;Bostwick et al, 2010;Clark and Feo, 2008). In many species, non-vocal sounds arise from air passage over specialized wing and tail feathers (e.g.…”

Section: Discussionmentioning

confidence: 99%

“…Many animals produce diverse non-vocal acoustic signals, termed sonations by some investigators. The mechanisms for these forms of sound production have only recently become a focus of investigation Prum, 2003, 2005;Bostwick et al, 2010;Clark and Feo, 2008).…”

Section: Introductionmentioning

confidence: 99%

Determination of the wingsnap sonation mechanism of the Golden-collared manakin (Manacus vitellinus)

Bodony

Day

Friscia

et al. 2016

Male golden-collared manakins (Manacus vitellinus), small suboscine passeriform birds of Panamanian forests, communicate acoustically using a variety of non-vocal sonations. The most prominent sonations are single or multiple intense 'wingsnaps' with a dominant acoustic frequency around 5 kHz. Several hypotheses have been proposed addressing the source of the sound, ranging from purely aerodynamic origins (due to a rapid jet of air formed by the wings or by a 'whiplike' motion) to purely structural origins (such as physical contact of the wings), but without definitive assessment. Using anatomical analysis as well as high-speed video and synchronized audio recordings, we show that compared with related species, M. vitellinus radii are morphologically unique and confirm that they collide over the back of the bird at the moment (±1 ms) the wingsnap is produced. Using aeroacoustic theory, we quantitatively estimate the acoustic signatures from several sonation mechanisms. We conclude that only the physical contact hypothesis, wherein the wing collisions create the sound, is consistent with the measured sonation.