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 fowls and of ducks is not great enough to account for the difference in resistance to the penetration of water. The peculiar quality of the plumage of swimming birds is its density. If you take up a fowl and examine the plumage you will find that it is easy to part the feathers so that the skin can be seen. It may be done with the fingers, or even by blowing gently among the feathers with the mouth. Now try to separate the feathers of a duck so that the skin will be visible. You find it much harder, because the feathers are so thick and soft and at the same time so elastic. The familiar phrase "like water from a duck's back" is not especially appropriate. The feathers on the back of most birds are a very effective protection against rain. The feathers all over a duck are such poor conductors of water that it is hard to remove them by scalding. The structure of the plumage of swimming birds adds to their buoyancy in the water. They do not have to exert themselves to remain on the surface, but float like cork.