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The aerodynamics of velvet: What humans can learn from owls

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To the ancient Greeks, the owl symbolized wisdom, but the Romans saw it as an evil omen. Their myths tell of an owl-like strix that stalked the night and preyed on human flesh. Ovid’s poem Fasti describes how such a demon slipped into the nursery of the sleeping prince Proca and was found hunched over the cradle, sucking the newborn’s blood. This supernatural owl changed over time. In Italian, strix became strega, meaning witch; in Romanian, strigoi is a vampire; and, in Macbeth, Shakespeare once more recast the owl as ‘the fatal bellman’ whose shriek summons King Duncan’s death. Like its legendary counterparts, the great gray owl, Strix nebulosa, inhabits the shadows. It lives in the icy north, in the dense, dark conifer forests of Russia, Alaska, and Canada. By night, it hunts. Scythe-like tal­ons and hooked, knife-sharp beak make the great gray owl a fearsome predator. By day, it stays hidden. Although one of the largest of its kind, its dusky and mottled plumage blends with the tree branches to atomize the bird’s silhouette, making it as nebulous and insubstantial as mist. Moreover, on a still moonlit night where snow blankets the landscape and deadens sound, the owl swoops on its quarry and barely breaks the silence.

This excerpt is from Sentient: How Animals Illuminate the Wonder of Our Human Senses, by Jackie Higgins (Atria Books, 2022) and was produced for the web by Earth | Food | Life, a project of the Independent Media Institute.

The quietness of the owl’s flight is unrivaled; its wing beat makes a sound so soft that it is nearly imperceptible. “While we’ve known this for centuries,” said Professor Nigel Peake of the University of Cam­bridge, “what hasn’t been known is how owls are able to fly in silence.” His laboratory is one of a few around the world trying to learn from this avian acoustic stealth. For years, the focus had been the feathers along the wing’s leading and trailing edges. Those at the front have tiny stiff barbs that point forward like the teeth of a comb, whereas those at the back are flexible and fringed. They work together to break up, then smooth the air currents as they flow over and off the wing, damping down any noisy turbulence. Recently Peake homed in on a third ele­ment: the wing’s luxuriant touch. “We were among the first to think about the aerodynamics of this velvet,” he told me. In 2016, he collabo­rated with scientists in America for a closer look at the smooth surface of wings from various owl species, including the great gray. They saw that the birds’ primary feathers were covered with a millimeter of fine fluff.

“Microscope photographs of the down show it consists of hairs that form a structure similar to that of a forest,” Peake explained. “The hairs ini­tially rise almost perpendicular to the feather surface but then bend over in the flow direction to form a canopy.” This Lilliputian ‘forest’ reduces pressure fluctuations and turbulence dramatically as the air flows over the wing. The researchers, funded by the U.S. National Science Foundation and the U.S. Office of Naval Research, recreated this topography in plastic. Testing their prototype in a wind tunnel, they found it reduced sound so well that they patented the de­sign. This discovery promises not simply stealthier surveillance aircraft or submarines but also a significant drop in everyday noise pollution from, say, wind turbines, computer fans, and even the passenger planes daily crisscrossing the planet.

“Owls have much to teach us about mak­ing our own world quieter,” said Peake. “No other birds have wings that scatter sound so their prey can’t hear them coming.” The great gray is neither seen nor heard, and this natural specter also seems endowed with a supernatural sense. From a distance of some 30 meters (100 feet), it can pinpoint mice or voles with uncanny precision, even those hidden beneath mounds of virgin snow.

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