Evidence that the Dorsal Velvet of Barn Owl Wing Feathers Decreases Rubbing Sounds during Flapping Flight

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Owls have specialized feather features hypothesized to reduce sound produced during flight. One of these features is the velvet, a structure composed of elongated filaments termed pennulae that project dorsally from the upper surface of wing and tail feathers. There are two hypotheses of how the velvet functions to reduce sound. According to the aerodynamic noise hypothesis, the velvet reduces sound produced by aerodynamic processes, such as turbulence development on the surface of the wing. Alternatively, under the structural noise hypothesis, the velvet reduces frictional noise produced when two feathers rub together. The aerodynamic noise hypothesis predicts impairing the velvet will increase aerodynamic flight sounds predominantly at low frequency, since turbulence formation predominantly generates low frequency sound; and that changes in sound levels will occur predominantly during the downstroke, when aerodynamic forces are greatest. Conversely, the frictional noise hypothesis predicts impairing the velvet will cause a broadband (i.e., across all frequencies) increase in flight sounds, since frictional sounds are broadband; and that changes in sound levels will occur during the upstroke, when the wing feathers rub against each other the most. Here, we tested these hypotheses by impairing with hairspray the velvet on inner wing feathers (P1-S4) of 13 live barn owls (Tyto alba) and measuring the sound produced between 0.1 and 16 kHz during flapping flight. Relative to control flights, impairing the velvet increased sound produced across the entire frequency range (i.e., the effect was broadband) and the upstroke increased more than the downstroke, such that the upstroke of manipulated birds was louder than the downstroke, supporting the frictional noise hypothesis. Our results suggest that a substantial amount of bird flight sound is produced by feathers rubbing against feathers during flapping flight.

Medienart:	E-Artikel

Erscheinungsjahr:	2020
Erschienen:	2020

Enthalten in:	Zur Gesamtaufnahme - volume:60
Enthalten in:	Integrative and comparative biology - 60(2020), 5 vom: 01. Nov., Seite 1068-1079

Sprache:	Englisch

Beteiligte Personen:	LePiane, Krista [VerfasserIn] Clark, Christopher J [VerfasserIn]

Links:	Volltext

Themen:	Journal Article Research Support, U.S. Gov't, Non-P.H.S.

Anmerkungen:	Date Completed 27.10.2021 Date Revised 27.10.2021 published: Print Citation Status MEDLINE

doi:	10.1093/icb/icaa045

funding:
Förderinstitution / Projekttitel:

PPN (Katalog-ID):	NLM31104767X