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(Katrina van Grouw)

The Unfeathered Bird

500 years after Leonardo, the mechanics of bird flight still enthralls.

Katrina van Grouw is a former curator of the ornithological collections at London’s Natural History Museum, and a graduate of the Royal College of Art. In her new book, The Unfeathered Bird (Princeton University Press, 2013), 385 exquisite drawings and straightforward prose offer insight into what goes on beneath the feathered surface. Van Grouw will be signing copies of her book at the Smithsonian Museum of Natural History on November 19, 2013.

Although they are powerful fliers in pursuit of prey, most raptors (Eurasian Buzzard, pictured above) are not capable of long periods of sustained flight; they need to conserve their energy for the chase. So the majority of groups rely on a passive approach to hunting: gazing out from a perch, hovering motionless in the wind, or using rising updrafts of warm air to keep them aloft while they look around them in search of food. Soaring birds have long, broad wings to provide an ample surface area to generate lift, and their deeply notched primary feathers create turbulence around the wingtips, which prevents stalling at low speeds. The ability to soar comes at a price, however. The Old World vultures went down the soaring route and lost much of their aerial maneuverability altogether.

Hummingbird

(Katrina van Grouw)

The skeletal structure of a hummingbird’s wing is similar to that of a swift—a short, stout, and queerly shaped upper arm, a short forearm, and a long and much enlarged hand section. Hummingbirds, however, move their wings in an entirely different way. Their wingtips describe a figure-eight shape in the air, generating lift on the backward as well as forward strokes rather like a helicopter, whereas most birds power themselves with the downward beat of their wings, using the upstroke merely as a recovery motion. Pictured at right: A white-throated hummingbird.

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