. Animal biology. Zoology; Biology. CLASS AVES 411 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 glidin
. Animal biology. Zoology; Biology. CLASS AVES 411 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 soaring, characterized by the bird, usually at a high elevation, describing great circles without any move-. FiG. 299.—Restoration of a bipedal dinosaur, Ornithomimus. "Reptiles and ;) {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. 430. 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 Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Wolcott, Robert Henry, 1868-1934; University of Nebraska (Lincoln campus). Dept. of Zoology. New York ; L
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