. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 302 ZOOLOGY largely a matter of adjustment to food supply. A migrant almost always depends to a large extent upon fruits, seeds, and grains as part of its food. Most winter residents, as the crow, are omniv- orous in diet. Others, as the sparrows, may be seed eaters, but under stress may change their diet to almost anything in the line of food; still others, as the woodpeckers, although insect-eating birds, manage to find the desired food tucked away under the bark of trees. Most insect-eat
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 302 ZOOLOGY largely a matter of adjustment to food supply. A migrant almost always depends to a large extent upon fruits, seeds, and grains as part of its food. Most winter residents, as the crow, are omniv- orous in diet. Others, as the sparrows, may be seed eaters, but under stress may change their diet to almost anything in the line of food; still others, as the woodpeckers, although insect-eating birds, manage to find the desired food tucked away under the bark of trees. Most insect-eating birds, however, because their food is found on green plants, are forced southward by the cold weather. Migrations are almost entirely due to need of food which cannot be obtained during a time when vegetation is dormant and the ground is frozen. Classification of Birds. — Birds are divided into two great groups, de- pending on the development of the keel, that is, the part of the sternum to which the muscles used in flight are attached. This bone is well known to every one who has ever picked the breastbone of a chicken. Hence all flying birds are placed in a group called the Carinatce. Birds in which the keel of the breastbone is not well de- veloped, such as the ostrich and cassowary, are said to belong to the Ratitce. These birds make up for their lack of wing de- velopment by having the legs strong and long. The flying birds are further subdivided into a number of orders, the classification based upon the adaptations of differ- ent parts of the bird, especially the legs and feet, the wings and the bill, to different func- tions. We shall not trouble ourselves to learn all the differ- ent groups, but shall content ourselves with picking out some of the more evident and important ones. I. Perching Birds.—To this order belong most of our common African ostrich {Struthio camelvs).. Please note that these images are extracted from scanned page images that may hav
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