S6-5 Sunday, Jan. 5 09:00 - 09:30 The dorsal velvet surface of owl feathers decreases sounds of rubbing during flapping flight LEPIANE, K/L*; CLARK, C/J; University of California, Riverside; University of California, Riverside firstname.lastname@example.org
One wing feature that owls have evolved to silence their flight is the velvet, made up of elongated filamentous projections, or pennula, that stick up on the dorsal surface of feathers. There are two hypotheses as to how the velvet silences flight: aerodynamic noise and structural noise. The aerodynamic noise hypothesis predicts silencing features reduce low frequency sound produced by turbulence development over the surface of the wing. This hypothesis predicts that impairing the velvet will increase low frequency sounds produced during the downstroke, when airspeed over the wing is greatest. Alternatively, the structural noise hypothesis predicts velvet reduces frictional noise, or broadband sound produced when two feathers rub together. Rubbing is likeliest during flapping flight. This hypothesis predicts that impairing the velvet will increase broadband sound produced during the upstroke, when wing deformation causes feathers to rub together. Further, this hypothesis predicts impairing the velvet on regions of feather overlap (trailing vane) will increase sound produced during flight and impairing an adjacent portion of the feather, where there is no feather overlap, will not. To test these hypotheses, we applied hairspray to the dorsal surface of five flight feathers (P1 - S4) on live Barn Owls (Tyto alba). We flew owls over a stationary microphone and recorded flight sounds at three experimental conditions: control, manipulation, and manipulation removed. Applying hairspray to flight feathers increased the broadband sound Barn Owls produce during the upstroke, supporting the structural noise hypothesis.