Auk, a general name for certain swimming birds common in the polar regions. There are but two species of the auks proper, the great auk and the razor-bill. The great auk, a bird about three feet in length, was formerly plentiful in the northern regions and was known to visit the British Isles, but within the knowledge of man it has become extinct. In museums, however, there are some seventy skins, a number of eggs and the skeletons of still more individuals. The wings of the great auk were only about six inches in length and totally useless for flight, but were employed vigorously as fins in swimming, especially while the bird was diving. The tail was about three inches long and the legs of the bird were placed so far back that when on land the bird seemed to stand erect. The head, neck and upper parts of the bird were black, but a large spot under each eye and most of the under parts were white. The razor-bill is about fifteen inches in length and can use its wings in flight. Thousands of these birds are killed on the coast of Labrador for their breast feathers, which are thick and warm. Among the species grouped with the auks are the tufted puffin and the rhinoceros auklet of the North Pacific, the black guillemot of the North Atlantic, the murre or common guillemot, which migrates from Spitzbergen southward to the New England states, and the little auk of Greenland and northern Iceland. These birds spend the winter in the open seas, but in spring they come to land, where each pair claims its little space of ground on which is laid its single egg. There are localities on the north-eastern coast of North America where thousands of these birds, sometimes representatives of several different species, may be seen sitting close together, each protecting its own egg, which it holds upon its webbed feet and covers with its body.