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article imageHummingbirds work hard in unfriendly skies (video)

By Tim Sandle     Apr 1, 2014 in Environment
Swirling air can make hummingbirds work harder to hover, according to a new study. This happens when the air’s vortices open wider than a bird’s wing.
The new study represents the first measurements of how much a flying animal’s metabolism revs up when coping with turbulent air. The examination was undertaken on five Anna’s hummingbirds (Calypte anna) by Victor M. Ortega-Jimenez of the University of California, Berkeley.
Hummingbirds are birds that constitute the family Trochilidae. They are among the smallest of birds, most species measuring in the 3–5 inches range. They are known as hummingbirds because of the humming sound created by their beating wings, which flap at frequencies audible to humans. They also have among the highest metabolisms of any animal.
Using a wind tunnel, Science reports, the researchers observed hummingbirds hovering at a feeder downwind from a cylinder of varying size. Buffeted by vortices of air whipping off slim cylinders (2 or 4 centimeters in diameter), the birds held their position without needing extra oxygen even with wind speeds of 9 meters a second, or about 20 miles per hour.
However when researchers used a 9-centimeter-wide cylinder, vortices widened to 173 percent of wing length, the hummingbird metabolisms increased some 25 percent on average — even at gentler wind speeds of 3 and 6 meters per second. Later study showed that the hummingbirds relied on asymmetric tail and wing motions to hover in place.
The findings have been reported to the journal Proceedings of the Royal Society B. The paper is titled “Into turbulent air: size-dependent effects of von Kármán vortex streets on hummingbird flight kinematics and energetics”.
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