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The Great Northern Diver, known in North America as the Common Loon (Gavia immer), is a large member of the loon, or diver, family of birds.

Adults can range from 61–100 cm (24–40 inches) in length with a 122–152 cm (4–5-foot) wingspan, slightly smaller than the similar White-billed Diver or "Yellow-billed Loon". The weight can vary from 1.6 to 8 kg (3.6 to 17.6 lbs). On average a Great Northern Diver is about 81 cm (32 inches) long, has a wingspan of 136 cm (54 inches), and weighs about 4.1 kg (9 lbs).

The Great Northern Diver breeds in Canada, parts of the northern United States, Greenland, and Alaska. There is a smaller population (ca. 3,000 pairs) in Iceland. On isolated occasions they have bred in the far north of Scotland. The female lays 1 to 3 eggs on a hollowed-out mound of dirt and vegetation very close to water. Both parents build the nest, sit on the egg or eggs, and feed the young.

This species winters on sea coasts or on large lakes over a much wider range in Europe and the British Isles as well as in North America.

Breeding adults have a black head, white underparts, and a checkered black-and-white mantle. Non-breeding plumage is brownish, with the chin and foreneck white. The bill is black-blue and held horizontally. The bill colour and angle distinguish this species from the similar White-billed Diver.

This species, like all divers, is a specialist fish-eater, catching its prey underwater, diving as deep as 200 feet (60 m). Freshwater diets consist of pike, perch, sunfish, trout, and bass; salt-water diets consist of rock fish, flounder, sea trout, and herring.

The bird needs a long distance to gain momentum for take-off, and is ungainly on landing. Its clumsiness on land is due to the legs being positioned at the rear of the body: this is ideal for diving but not well-suited for walking. When the birds land on water, they skim along on their bellies to slow down, rather than on their feet, as these are set too far back. The loon swims gracefully on the surface, dives as well as any flying bird, and flies competently for hundreds of kilometers in migration. It flies with its neck outstretched, usually calling a particular tremolo that can be used to identify a flying loon.

The source: Wikipedia