As a family the Loons are relatively very old, two or more fossil representatives having been discovered in the lower Miocene of France and the Pliocene of England, but so far as we are able to determine they did not differ essentially from the modern representatives, showing that the latter have changed but little with time. They are birds of large size, ranging between twenty-four and thirty-eight inches in length, and are past masters in the art of swimming and diving. They present a very awkward appearance on land, since the legs are placed far back on the body, but the water is their natural element, and they are perhaps the most expert divers known among birds, diving so quickly that it is almost impossible to shoot one, when it is alert, even with a rifle. Although they have well-developed and rather strong wings, they rise from the water with more or less difficulty, but when once under way their flight is exceedingly swift and as straight as an arrow. The sexes are alike in plumage, although there is considerable difference between the summer and winter dress as well as between adults and downy young. They are blackish or slaty above and white beneath, becoming in summer thickly spotted or speckled with white, while the throat and fore neck are blackish or chestnut. In winter plumage and in the young the white markings are absent from the upper parts and the throat and fore neck are white like the remainder of the lower parts. They are circumpolar in distribution, the five recognized species being referred to a single genus (Gavia). Unlike their relatives the Auks, they are not at all gregarious or sociable, being usually found singly or in pairs, though occasionally in winter they are forced to crowd together when there is a limited surface of open water in which they can feed. They are found during the nesting season throughout the cooler parts of the northern hemisphere, even well within the Arctic circle, but during the win-ter they are widely spread throughout temperate regions, and especially along the adjacent oceans. Knowing that man is its mortal enemy, it is constantly on the watch. When it meets a passing boat it widens the distance by immediately sheering off, and prefers to escape pursuit by diving rather than flying, remaining under water so long and coming to the surface at so great a distance from its would-be captor, and in such unexpected places, that its pursuit is rendered tedious and often unavailing. In spring they repair to the more secluded lakes and ponds for the purpose of rearing their young. The nest is a rude affair of grass, moss, and often a little mud, placed on the ground at the edge of a marsh or lake, often on an abandoned muskrat “house,” a bog, or other slight elevation in shallow water. There is no attempt at concealment, but the nest is usually so placed as to permit of uninterrupted vision in all directions, so that the moment danger threatens the parent slips silently into the water and is gone. The eggs are, however, adapted for concealment, being dark brown or olive, speckled or spotted with brown or blackish, thus harmonizing with the grass lining of, the nest. The eggs, two in number, are elongate-ovate in shape and of large size. The cry of the Loon is exceedingly loud and melancholy, being likened by some to the howl of a wolf or the prolonged scream of a human being in deep distress. It is frequently uttered at night, or in early morning when nature is otherwise silent, and the effect upon the startled listener is often one of fright and horror. They feed entirely upon fish, which they are adepts in capturing. The following account is from the pen of Dr. Coues, and refers to the Pacific Loon (Gavia pacifica), which he once found surprisingly tame about the bay of San Pedro in southern California: “Now two or three would ride lightly over the surface, with neck gracefully curved, propelled with idle strokes of their paddles to this side and that, one leg, often the other, stretched at ease almost horizontally backward, while their flashing eyes, first directed upward with sidelong glance, then peering into the depths below, sought for some attractive morsel. In an instant, with the peculiar motion, impossible to describe, they would disappear beneath the surface, leaving a little foam and bubbles to mark where they went down, and I could follow their course under water; see them shoot with marvelous swiftness through the liquid element, as, urged by the powerful strokes of the webbed feet and beats of the half-opened wings, they flew rather than swam; see them dart out the arrow-like bill, transfix an unlucky fish, and lightly rise to the surface again.”
The characters upon which the species of Loon are based, although not very striking, are ordinarily sufficient for their ready identification. Thus the first four species to be mentioned agree in having the tarsus shorter than the middle toe without the claw, and in having the fore neck blackish in summer. In the so-called Common Loon (G. Imber) the bill in the mature bird is blackish and the head and neck are glossed with velvety green; the length is from twenty-eight to thirty-six inches. This bird is found throughout the northern part of the Northern Hemisphere. Its closest relative is the Yellow-billed Loon (G. Adamsii), so named from the fact that the bill is almost wholly yellowish white, while the head and neck are glossed with velvety violet-blue. It is also the largest species, ranging from thirty-five to thirty-eight inches in length, and in-habits western Arctic America and northeastern Asia. These two species have the head and neck black all around, while in the two following these parts are grayish. Of these the Black-throated Loon (G. Arctica) is so called from the blackish fore neck, this being glossed with velvety purple. It is smaller than either of those above mentioned, being from twenty-six to twenty-nine inches long. It ranges over the northern portions of the Northern Hemisphere, breeding in the Arctic regions. Very closely allied is the Pacific Loon (G. Pacifica), being distinguished by its smaller size and the paler color of the nape and back of the head ; it is confined to the Pacific coast of North America. In the remaining form, the Red-throated Loon (G. Lumme), the tarsus is longer than the middle toe with its claw, and the fore neck is a rich chestnut. It is widely distributed over the northern portion of the Northern Hemisphere, nesting well within the Arctic regions.