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One can tell a great deal about how a bird lives just from its wing shape. Most passerines, doves, woodpeckers, and game birds have wings that taper down more or less to a point at their outer tip. Those wings have a low aspect ratio (ratio of length to width), designed for rapid takeoff and swift twisting flight, but not for sustained high speed. Narrowing the tips reduces the area subject to the drag-inducing formation of vortices. At each wingtip a spiraling vortex is formed as air spills from the high-pressure area under the wing into the low-pressure area over it. Tapering, low-aspect-ratio wings are found on birds that must be fast and agile in order to outmaneuver both their prey and their predators.
Slots between feathers at the tip of the wing lower the speed at which air flowing over the wingtip can cause enough turbulence to initiate a "stall" (reducing lift so that the bird starts descending). Slots thus aid low-speed maneuvering and are better developed in small, agile birds such as wood warblers than in less-active species such as House Sparrows. They are also prominent features on the wings of crows and their relatives and of game birds. Flat, rather high-aspect-ratio wings lacking slots, and with feathers at the base that streamline the trailing edge in with the body, are found in falcons, swallows, plovers, and other specialists in high-speed flight. In contrast, hawks that soar in open country have lower-aspect-ratio wings; and Sharp-shinned Hawks that hunt in woodlands (and owls that also hunt there) and must be able to turn rapidly have an even lower aspect ratio. Wings that are more cambered (arched in cross section), with low aspect ratio and well-developed slots, characterize vultures and other soaring land birds, while extremely high-aspect-ratio wings characterize albatrosses and other oceanic "slope soarers." SEE: Soaring; Hovering Flight. Copyright ® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl Wheye. |
