Title: Animal biology
Identifier: animalbiology00wolc (find matches)
Year: 1933 (1930s)
Authors: Wolcott, Robert Henry, 1868-1934
Subjects: Zoology; Biology
Publisher: New York ; London : McGraw-Hill Book Company, Inc.
Contributing Library: MBLWHOI Library
Digitizing Sponsor: MBLWHOI Library

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398 METAZOAN PHYLA The tip of the wing traces a path in the air which is characterized by long downward and forward strokes, alternating with shorter upward and backward strokes. This action is modified in other modes of flight. After making several strokes, some birds hold their wings motionless and glide for a considerable distance before again making several more. Thus gliding is a second form of flight. In some cases before a high wind a bird will partly flex the wings and permit itself to be carried by the wind. This is a form of flight known as flex gliding. Another modification of flight is known as soarir.g, characterized by the bird, usually at a high elevation, describing great circles without any move-
Text Appearing After Image:
FiG. 27.3.—Restoration of a bipedal dinosaur, Ornithomimus. "Reptiles and Amphibians.'^) (Redrawn from Barbour, ments of the wings whatever. As it describes these circles it gradually works along with the wind. There is no doubt that soaring is usually due to the bird taking advantage of the upward rush of currents of air, though it may be that the bird can soar by taking advantage of a wind blowing horizontally. Still another form of flight is known as hovering, in which the bird remains poised in the air before a flower or above an object upon the ground, the tip of its wings apparently describ- ing a figure eight. 428. The Bird as a Flying Animal.—A bird flies on the principle of an airplane, or heavier-than-air machine, rather than on that of a balloon, or lighter-than-air machine. Such a machine requires light- ness and rigidity, which are secured by the character of the bird's skeleton.

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