http://www.nytimes.com/2008/03/04/science/04angi.html

In the latest issue of the journal Science, Anders Hedenstrom of Lund University in Sweden and his colleagues report that when a nectar-eating bat hovers in midair to sip liquid sugar, the mammal’s sharp-edged flexible wings generate the same sort of precision whirlwind lift detected recently in studies of insect flight. As the bat curls its membranous flappers in and out three times per second, a series of tiny cyclones form at the leading edge of each wing. The result? Even as gravity plucks at its heels, the bat’s homegrown tornadoes suck it back up toward Oz.

Other researchers have demonstrated that insects like honeybees and dragonflies rely on such leading-edge vortices to supply the major part of their lift, particularly during a hover or slow cruise. The new work shows that considerably heavier animals than insects can rally the power of quick-changing or “unsteady” aerodynamic tactics in their quest to stay high. The star of the current study, the Pallas’s long-tongued bat of Latin America, weighs maybe 12 grams, 120 times greater than the average bee. The researchers predict that hummingbirds will also be shown to have twister-tipped wings.