. The bird, its form and function. Birds. 368 The Bird curved, and in a neglected aviary I have seen birds which were prisoners on their perch, unable to untwist their claws from it. When wild, birds wear down these struc- tures by constant rubbing, and if given plenty of rough bark and wood in their cages, their claws will remain of usual length. Although the tarsus, or that portion of the foot which we usually call the leg, is, in almost all birds, covered with horn)' scales, 3'et these vary con- siderabh' in different groups. In many the scales are small, six- sided or oblong, as in plovers
. The bird, its form and function. Birds. 368 The Bird curved, and in a neglected aviary I have seen birds which were prisoners on their perch, unable to untwist their claws from it. When wild, birds wear down these struc- tures by constant rubbing, and if given plenty of rough bark and wood in their cages, their claws will remain of usual length. Although the tarsus, or that portion of the foot which we usually call the leg, is, in almost all birds, covered with horn)' scales, 3'et these vary con- siderabh' in different groups. In many the scales are small, six- sided or oblong, as in plovers. In some of the higher song-birds these scales have become joined together until, as in our robin, the front of the leg is covered with a long "boot" of horn. The cause of this coalescence yet remains to be discovered. A considerable degeneration of the legs and feet is found among goatsuckers, humming- birds, and chimney swifts; but, small as are the feet of the latter birds, they make frequent use of them to break off the short twigs which are used in the construction of their nests. One may take a young swift and place it against the vertical surface of an ordinary brick (Fig. 326), and the bird will hold fast without slipping a fraction of an inch. The slender nails fasten in the slightest irregularity of the surface and hold the bird safely. Some species of swifts have all four toes pointing. Fig. 289. -Foot of American 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 Beebe, William, 1877-1962. New York, Holt
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectbirds, bookyear1906
