Wing loadingThe relationship between the surface area of the wings and the bird's weight. The higher the weight in proportion to the wing area, the high is the wing loading. A bird with a low wing loading, such as a harrier (genus Circus), is more agaile in the air and can fly more slowly than one with a high loading, such as a swan (genus Cygnus).
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From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver