largely a matter of adjustment to food supply. A migrant almost always depends to some extent upon fruits, seeds, and grains as part of its food. Most winter residents, as the crow, are omnivorous 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, depending 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 Carinatæ. Birds in which the keel of the breastbone is not well developed, such as the ostrich and cassowary, are said to belong to the Ratita. These birds make up for their lack of wing development 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 different parts of the bird, especially the legs and feet, the wings and the bill, to different functions. We shall not trouble ourselves to learn all the different 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 birds, African ostrich (Struthio camelus). - sparrows, swallows, larks, blackbirds, orioles, kingbirds, and many others well known to every bird lover. In this group the toes are so placed, three toes being turned forward and one backward, as to be perfectly adapted to perching. A large number of our sweetest songsters belong among the perchers, the warblers, wrens, thrushes, bluebirds, and last but not least, our robin. II. THE FOWLS OR GALLINACEOUS BIRDS. This order is of great economic importance. From the jungle fowl, found wild in the jungles of India, all our domesticated fowls have arisen. Other familiar exam White-throated sparrow (Zonotrichia albicollis). ples are the turkeys, quails, partridge or ruffed grouse, and the pheasants and prairie chickens. In this group the legs are strong and stout, the body thickset, the bill and claws rather blunt. Birds of this order do not fly far in a state of nature, preferring to live on or near the ground. Such birds as the ruffed grouse, which nest on the ground, are almost invariably protectively colored. Ptarmigan in winter. Davison, Zoology. Another interesting example of protective resemblance in this group is seen in the ptarmigan. This bird in the winter is white as the snow which surrounds it; in the spring it molts, turning to a gray and white, thus resembling the lichens among which it feeds. III. BIRDS OF PREY. These birds are characterized by the strong hooked beak, adapted to tearing, and by the sharp claws, which are curved and strong. The need of a gizzard, which is a promincnt part of the digestive tract in a grain-eating bird, has here almost completely disappeared, the crop serving to macerate the food. Owls show this use of the muscular gullet and crop, for the hair and skeletons of the mice which form their prey are ejected in a small ball, by means of the gullet organ. Members of this group that Golden eagle (Aquila chrysaetos). North America and Europe. Copyright, 1901, by N.Y. Zoological Society. Sandhill crane, showing habitat. From mounted group at the American Museum of Natural History. the feet webbed, the wings are often adapted for long and swift flight. In this division are placed the gulls, terns, ducks, geese, loons, auks, and puffins. OTHER ORDERS. Other orders of birds which we are likely to see and recognize may be mentioned. They include the doves, the only remaining native representative being the mourning dove; the woodpeckers, strong and long of bill, the friend of the lumberman as a savior of the trees from boring pests which live under the bark; the swifts and humming birds, the latter among the tiniest of all vertebrate animals; and the parrots, of which we have only one native form, the Carolina paroquet (Conurus carolinensis). This bird once had a range north as far as the Great Lakes; now it is found only in South America. RELATIONSHIP OF BIRDS AND REPTILES. The birds afford an interesting example of how the history of past ages of the earth has given us a clew to the structural relation which birds bear to other animals. Several years ago, two fossil skeletons were found in Europe of a birdlike creature which had wings and feathers, but also teeth and a lizardlike tail. From these fossil remains and certain structures (as scales) and habits (as the egg Common tern (Sterna hirundo) and young, showing nesting and feeding habits. laying habits), scientists have concluded that birds and reptiles in distant times were nearly related and that our existing birds probably developed from a reptilelike ancestor millions of years ago. CLASSIFICATION OF BIRDS DIVISION I. Ratitæ. Running birds with no keeled breastbone. ostrich, cassowary. DIVISION II. Carinatæ. Birds with keeled breastbone. Examples, Beak stout. ORDER 1. Passeres. Perching birds; three toes in front, one behind. One half Hooked beak. Strong claws. Exam Long neck, beak, and legs. Examples, snipe, crane, heron. |