desirable because it gives greater brilliance to the plumage.

Fig. 2. White Leghorn chicks (ten days old)

Growth and molting of feathers. The first covering of a young bird is down. The young of birds which nest on the ground have the down covering when hatched; others acquire it in a few days. In small land birds which feather quickly, as Leghorn and Hamburg chicks, the largest wing feathers may have started to grow before the chick leaves the egg. In most kinds of poultry, however, the young show no signs of feathers for some days. The down is gradually replaced by small feathers, and these by larger feathers as the bird grows. As feathers in all stages of growth are found on the young bird at the same time, it is not known whether all feathers are molted the same number of times. In cases where some feathers were marked and watched, or where the colors changed with the changing feathers, it appeared that after the down three sets of feathers were grown in succession, the third and last making the adult plumage of the bird. This coat remains until the following summer or fall, when it is molted and replaced by a new one.

Flight. The habit of flying is objectionable in domestic birds because it makes them more difficult to control. It has no direct use except in pigeons kept for flying. There is, however, a very important connection between development for flying and the value of birds for the table. The muscles of the wings furnish the greater part of the edible meat of most birds. The most desirable birds for food purposes are those which have the wing muscles well developed, yet not quite strong enough to enable them to fly easily. In such birds the breast meat remains comparatively soft through life, while in birds that fly well it becomes hard in a very short time. That is why the breast meat of the pigeon is relatively tougher in an old bird than the breast meat of a fowl or turkey.

The balance between capacity for flight and neglect to use it, which is desired in birds grown for the table, is secured by giving them opportunity to exercise their wings moderately but not for progressive practice in flying, which would soon enable them to fly easily over the fences used to confine them. To regulate such exercise the perches for birds that roost are made low, or in an ascending series in which each perch after the first is reached from the one below it, while fences are made so much higher than the distance the bird is accustomed to fly that the failures of its first efforts to go over them discourage it. Ducks and geese, which do not roost, flap their wings a great deal, and if they have room often exercise them by half running and half flying along the ground.

Mechanism of the wing. In its structure and in the muscular power that moves it, the wing of a bird is a wonderful piece of mechanism. A bird in flying strikes the air with its wings so rapidly that the movements cannot be accurately counted. The heron, which is a slow-flying bird, makes from one hundred twenty to one hundred fifty downward strokes of its wings a minute. As each downward stroke must be preceded by an upward stroke, this means that the wings make from two hundred forty to three hundred separate movements a minute. In such swift-flying birds as the pigeon the movements of the wings can be distinguished but cannot be counted. The fastest movements of the wings are not made by the swiftest fliers. In order to fly at all some land birds with comparatively small wings have to move them so fast that the movements make a blur and a whirring noise. The partridge is an illustration of a bird of this class.

If the supporting surface of the wing of a bird were made of skin, like the web of the foot of a swimming bird, it would be necessary to fold the wing for each upward stroke. It is here that the structure of feathers adapts itself to the rapid action required for movement in the air. The wing is not one surface but a series of narrow surfaces lapping in such a manner that they unite to form one broad surface when the downward stroke is made, and with the upward stroke are separated so that the air passes between them. Greater power in the downward stroke and less resistance in the upward stroke are also secured by the curvature of the wing. The under side is concave, the upper side convex. Thus in the downward stroke the wing gathers the air under it and so increases the pressure, while in the upward stroke it scatters the air and reduces the pressure.

If the wing were equally rigid throughout, the movement of the bird would be mostly upward. The bird in flying moves forward because the front of the wing is rigid and the tips of the feathers, which are directed backward, are flexible. So the air compressed by the wing in the downward stroke escapes backward, and in doing so propels the bird forward. The principle is the same that is applied in the screw propeller of a boat or an airship, except that the wing vibrates while the propeller revolves.

The most important function of the tail in flight is to balance the bird. It is of some assistance in steering, but a bird steers its course mostly by manipulation of the wings.

Scratching. With the exception of the aquatic birds and the ostrich, all the species of poultry belong to the group called by naturalists Rasores or Scratchers. Birds of this class have legs of moderate length and very strong, with toes terminating in a stout claw. Normally they have three toes upon which the foot rests when they are standing on a flat surface, and a fourth toe, like a thumb, which assists the other toes to grasp a perch. Some individual birds and some races of birds have the fourth or hind toe double. The leg of a bird is so constructed that when it is bent as the bird sits on a narrow support the toes contract and grasp the support and hold it without any effort on the part of the bird. Thus the bird is as secure in its position on a limb when asleep as if wide awake and looking out for itself.

In proportion to their ability to scratch, birds are able to find seeds and insects concealed among dead or living vegetation on the surface of the ground, and also to dig below the surface. Scratching capacity is most highly developed in the fowl. Compared to it the other land birds are very feeble scratchers, and do little damage by scratching if free to roam about. For ages the scratching propensity of fowls was regarded as a vice in them, but since people began to give special attention to poultry they have learned that fowls are much more contented and thrifty in confinement if their food is given them in a litter of leaves, straw, or shavings, in which they must scratch for it, and have also found that to some extent fowls may be used to cultivate crops while destroying insects and weeds among them.

Swimming. Capacity for swimming has an economic value in domestic birds because it adapts those possessing it to places which land birds rarely frequent. It will be shown when the different kinds of aquatic birds are described that each has its special place and use in domestication.

The swimming faculty in these birds is of further interest because of its relation to the development of the body plumage. If a land bird is placed in the water, the feathers are quickly saturated, the water penetrating to the skin. A duck or other swimming bird will remain in the water for hours without the water penetrating the feathers. This is commonly supposed to be due to the presence of a large amount of oil in the feathers, but the difference in the oiliness of the feathers of