Owl Silent Swoop Depends On Down

貓頭鷹的羽毛非常柔軟，翅膀羽毛上有天鵝絨般密生的羽絨，因而貓頭鷹飛行時產生的聲波頻率小于1千赫。而一般哺乳動物的耳朵是感覺不到那么低的頻率，這樣無聲的出擊，使貓頭鷹的進攻有如閃電般迅速。

Unlike the wings of most birds， an owl’s wings have structures， including a downy surface that render their flight virtually noiseless.

We’ve known that the leading edge of an owl’s wing has a comb of stiff feathers. And the trailing edge has a flexible fringe， unlike the rigid trailing edge of a conventional bird wing. These two features contribute to a structure that produces almost no noise as it rushes through the air.

Now it appears that these predators have a third trick up their sleeves—or rather， wings—that allow them to be so silent but deadly.

Researchers modeled the effect of the layer of down on the wing，s top surface. The work was presented at a meeting of the American Physical Society’s Division of Fluid Dynamics.

Mimicking owl wing down may lead to new sound-proofing materials. Down and the other silencing features could inspire wind turbines and plane engines that produce less noise and fewer vibrations. So that all we hear is silence.

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