The great northern loon (Gavia immer), is a large member of the loon, or diver, family of birds. The species is known as the common loon in North America and the great northern diver in Eurasia; its current name is a compromise proposed by the International Ornithological Committee.
The great northern loon is one of the five loon species that make up the genus Gavia, the only genus of the family Gavidae and order Gaviiformes. Its closest relative is the other large black-headed species, the yellow-billed loon or white-billed diver, Gavia adamsii.
The genus name Gavia was the Latin term for the smew (Mergellus albellus). This small sea-duck is quite unrelated to loons and just happens to be another black-and-white seabird which swims and dives for fish. It is not likely that the Ancient Romans had much knowledge of loons, as these are limited to more northern latitudes and since the end of the last glacial period seem to have occurred only as rare winter migrants in the Mediterranean region. The specific name immer is derived from North Germanic names for the bird such as modern Icelandic "Himbrimi". The term is related to Swedish immer and emmer, the grey or blackened ashes of a fire, referring to its dark plumage; or to Latin immergo, to immerse, and immersus, submerged.
The European name "diver" comes from the bird's habit of catching fish by swimming calmly along the surface and then abruptly plunging into the water. The North American name "loon" is a reference to the bird's clumsiness on land, and is derived from Scandinavian words for lame, such as Icelandic "lúinn" and Swedish "lam". Having large webbed feet, the loons are efficient predators, powerful swimmers, and adroit divers.
Adults can range from 61 to 100 cm (24 to 39 in) in length with a 122–152 cm (48–60 in) wingspan, slightly smaller than the similar yellow-billed loon (or "white-billed diver"). The weight can vary from 1.6 to 8 kg (3.5 to 17.6 lb). On average, a great northern loon is about 81 cm (32 in) long, has a wingspan of 136 cm (54 in), and weighs about 4.1 kg (9.0 lb).
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 yellow-billed loon.
Bone structure: A number of solid bones (unlike normally hollow avian bones), which add weight but help in diving.
The great northern loon breeds in North America, Greenland, Iceland, and Great Britain. This species winters on sea coasts or on large lakes of south Europe and North America, and south to north-western areas of Africa.
