Why Owls Fly Silently

The story

Flap a piece of paper near your ear. Hear that? Whoosh, whoosh. Now imagine wings a metre wide, beating hard, right over your head — and hearing... almost nothing at all.

That is an owl. Many owls fly so quietly that if one glided past you in the dark, you would probably never know. Scientists have flown owls past sensitive microphones, and at many pitches the owls flew far more quietly than other birds. Owls are among the quietest fliers in the whole bird world. So how do they do it?

The secret is written on its feathers, in three parts.

Part one: the front edge of a hunting owl's wing carries something most birds lack — a row of tiny stiff bristles, like a little comb. As the wing cuts the air, the comb smooths and softens the rushing whoosh. Scientists are still studying exactly how the trick works — which owls love, presumably, being creatures of mystery.

Part two: many of the wing feathers have soft, fringed edges, like the edge of a silky scarf — scientists think these fringes help hush the wing, perhaps partly by softening how the air leaves it.

And part three: the tops of the wing feathers wear a fine velvety surface, soft as a whisper — which helps quiet the wing, partly, scientists think, by hushing the tiny sounds of feather brushing against feather.

Comb in front, fringe behind, velvet on top. The owl flies quietly partly because its big wide wings let it fly SLOWLY — and partly because those special feathers take the noise apart.

Why? Probably dinner. An owl hunts little animals with very sharp ears — a noisy wing could warn the meal away. And scientists think the quiet helps another way too: it keeps the owl's OWN ears clear, so it can hear the tiny rustle of its supper far below while it flies.

Now here is where the story leaves the forest. In Japan, an engineer named Eiji Nakatsu worked on the famous bullet trains — trains that travel as fast as a small aeroplane. His trains had a noisy problem: the part on the roof that touches the electric wires whooshed terribly at high speed. And Nakatsu happened to love birdwatching. He thought of the owl — the little comb on the front of its wing — and his team reshaped part of the noisy piece with small owl-inspired jags and points. The whoosh shrank, and the trains ran quieter — thanks, in part, to an owl.

Copying nature's homework like this even has a name: biomimicry. Nature has been testing designs for millions of years; the owl's wing is one of its finished masterpieces.

Right now, somewhere in the dark, an owl is gliding so quietly that the little animals below may never hear it coming. And in Japan, trains have hushed past sleeping towns with the owl's secret in their design — engineers borrowing nature's quiet tricks, as they do to this day.