The red-throated loon (North America) or red-throated diver (Britain and Ireland) (Gavia stellata) is a migratory aquatic bird found in the Northern Hemisphere. The most widely distributed member of the loon or diver family, it breeds primarily in Arctic regions, and it winters in northern coastal waters. Ranging from 55 to 67 centimetres (22 to 26 in) in length, the red-throated loon is the smallest and lightest of the world's loons. In winter, it is a nondescript bird, greyish above, fading to white below. During the breeding season, it acquires the distinctive reddish throat patch, which is the basis for its common name. Fish form the bulk of its diet, though amphibians, invertebrates, and plant material are sometimes eaten as well. A monogamous species, red-throated loons form long-term pair bonds. Both members of the pair help to build the nest, incubate the eggs (generally two per clutch), and feed the hatched young. The red-throated loon has a large global population and a significant global range, though some populations are declining. Oil spills, habitat degradation, pollution, and fishing nets are among the major threats this species faces. Natural predators—including various gull species, and both red and Arctic foxes, will take eggs and young. The species is protected by international treaties.
Taxonomy and etymology First described by Danish naturalist Erik Pontoppidan in 1763, the red-throated loon is a monotypic species with no distinctive subspecies despite its large Holarctic range. Pontoppidan initially placed the species in the now-defunct genus Colymbus, which contained grebes as well as loons. By 1788, German naturalist Johann Reinhold Forster realized that grebes and loons were different enough to warrant separate genera, and moved the red-throated loon (along with all other loon species) to its present genus. Its relationship to the four other loon species is complex; although all belong to the same genus, it differs from the others in terms of morphology, behaviour, ecology and breeding biology and may be the sister group to all other species in the genus. Analysis of molecular data together with the fossil record suggests the lineage of the red-throated loon diverged from that giving rise to the other loon species around 21.4 million years ago in the Miocene, and that it may be most closely related to the fossil Pliocene species Gavia howardae. The red-throated loon is thought to have evolved in the Palearctic, and then to have expanded into the Nearctic. The genus name Gavia comes from the Latin for "sea mew", as used by ancient Roman naturalist Pliny the Elder. The specific epithet stellata is Latin for "set with stars" or "starry", and refers to the bird's speckled back in its non-breeding plumage. Members of the family Gavidae are known as loons in North America and divers in Great Britain and Ireland. The International Ornithological Congress uses the name red-throated loon for this species. "Diver" refers to the family's underwater method of hunting for prey, while "red-throated" is a straightforward reference to the bird's most distinctive breeding plumage feature. The word "loon" is thought to have derived from the Swedish lom, the Old Norse or Icelandic lómr, or the Old Dutch loen, all of which mean "lame" or "clumsy", and is a probable reference to the difficulty that all loons have in moving about on land. A local name from Willapa Harbor, Washington, was Quaker loon.
Description Like the other members of its genus, the red-throated loon is well adapted to its aquatic environment: its dense bones help it to submerge, its legs—in their set-back position—provide excellent propulsion, and its body is long and streamlined. Even its sharply pointed bill may help its underwater streamlining. Its feet are large, its front three toes are fully webbed, and its tarsus is flattened, which reduces drag and allows the leg to move easily through the water. The red-throated loon is the smallest and lightest of the world's loon species, ranging from 53 to 69 cm (21 to 27 in) in length with a 91–120 cm (36–47 in) wingspan, and weighing 1–2.7 kg (2.2–6.0 lb). Like all loons, it is long-bodied and short-necked, with its legs set far back on its body. The sexes are similar in appearance, although males tend to be slightly larger and heavier than females. In breeding plumage, the adult has a dark grey head and neck (with narrow black and white stripes on the back of the neck), a triangular red throat patch, white underparts, and a dark grey-brown mantle. It is the only loon with an all-dark back in breeding plumage. The non-breeding plumage is drabber with the chin, foreneck, and much of the face white, the top of the head and back of the neck grey, and considerable white speckling on the dark mantle. Its iris is carmine-red to burgundy in colour, its legs are black on the outer half and pale on the inner half, and the webs of its feet are pinkish-brown, with darker margins. Its bill is thin, straight, and sharp, and often held at an uptilted angle. One of the bird's North American folk names is pegging-awl loon, a reference to its sharply pointed bill, which resembles a sailmaker's awl (a tool also known as a "pegging awl" in New England). Though the colour of the bill changes from black in summer to pale grey in winter, the timing of the colour change does not necessarily correspond to that of the bird's overall plumage change. The nostrils are narrow slits located near the base of the bill.
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