Wing loading
The 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).From Peter Weaver's Birdwatcher's Dictionary
Copyright © 1981 by Peter Weaver