Friday, January 29, 2016

Silent But Deadly

Drawing Barred Owl feather

Owls are the living example of the old adage “seen but not heard.”  Did you ever wonder whether the myth of their silent flight is true or just an exaggeration? Last fall we took our dog for a walk on a moonlit night upstate, and we saw a strange sight.  Up in a tree in front of our house sat an owl with a large glittering golden red object in its mouth.  Next to that owl sat another saying “hoo” (really saying it) “who cooks for you?”  Then the second owl spread its wings and flew off—silently, so silently that the air seemed to stop moving.  With a closer look, I could see that the first owl had a huge koi in its mouth, probably taken from a nearby homeowner’s koi pond.  The owl looked at me with those deep coal black eyes and sat there.  These were barred owls, and we have a pair of them upstate.  They probably mostly eat mice and small rodents as they are known to do, but occasionally they may come upon a surprise feast of a frog or even a koi.  They love fish and aquatic animals, love to eat them that is. 

But getting back to the question of silent flight, I had questions.  These are big birds with big wings—how could they not make a sound when they fly?  Well, I am taking a Birds of Prey drawing course at the NY Botanical Gardens, and I am drawing a barred owl for my project.  I took a closer look (online—I know we are not legally allowed to have owl feathers) and got my answer.  Owl feathers have a unique construction with a couple of special features that dampen sound built right into them.  

Diagram from How Stuff Works

Owl feathers have downy hairs all over their surface that break the air stream into smaller air streams that dissipate the sound, so there is no build up of a single audible air pressure wave.  Not only that, but the primary flight feathers are serrated like a comb. This design breaks down turbulence into smaller currents or micro-turbulences. The edge muffles thesound of air flowing over the wing and shifts the angle at which air flows. This allows air to pass through which eliminates sound. Some researchers think that the feathers could also shift the sound energy of the wing to a higher frequency that their prey and human watchers cannot hear.  As you can imagine, the military and various other makers of aircraft are studying this and trying to duplicate it to reduce aircraft noise.  Feathers in general are wonderful to draw, but owl feathers are especially interesting because they have an almost magical quality to them.  No wonder Athena and Lakshmi both revered the silent flying owls and kept them safe from harm.

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