Red-throated loon

Appearance

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 in length with a 91–120 cm wingspan, and weighing 1–2.7 kg. 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, 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 color, 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. 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.

Distribution

The red-throated loon breeds primarily in the Arctic regions of northern Eurasia and North America, and winters in northern coastal waters, sometimes in groups of considerable size. More than 4,400 spend the winter in a loose concentration on the eastern part of the German Bight, for example. Unlike other loons, it regularly uses very small freshwater lakes as breeding sites. Its small size renders it more versatile, but it is less able to feed on deeper prey. The increase in size and diversity of the remaining species of loons suggests that the benefits of larger size outweigh the limitations.

Status

Although the red-throated loon is not a globally threatened species, as it has a large population and a significant range, there are populations which appear to be declining.

Behavior

Because its feet are located so far back on its body, the red-throated loon is quite clumsy walking on land, but it can use its feet to shove itself forward on its breast. Young use this method of covering ground when moving from their breeding pools to larger bodies of water, including rivers and the sea. It is the only species of loon able to take off directly from land. If frightened, it may submerge until only its head or bill shows above the surface of the water.

The red-throated loon is a diurnal migrant, which travels singly or in loose groups, often high above the water. In eastern North America , it tends to migrate near the coast rather than farther offshore; Siberian populations travel for hundreds of miles over land en route to their southern European wintering grounds.

It is a strong flier, and has been clocked at speeds between 75 and 78 kilometres per hour. Like all members of its family, the red-throated loon goes through a simultaneous wing moult, losing all its flight feathers at once and becoming flightless for a period of three to four weeks. Unlike other loons—which undergo this moult in late winter—the red-throated loon loses its ability to fly sometime between late summer and late autumn.

Reproduction

The red-throated loon is a monogamous species which forms long-term pair bonds. Both sexes build the nest, which is a shallow scrape lined with vegetation and sometimes a few feathers, and placed within a half-metre of the edge of a small pond. The female lays two eggs; they are incubated for 24–29 days, primarily by the female.

The eggs, which are greenish or olive-brownish spotted with black, measure 75 mm × 46 mm and have a mass of 83 g, of which 8% is shell. Incubation is begun as soon as the first egg is laid, so they hatch asynchronously. If a clutch is lost before the young hatch, the red-throated loon usually lays a second clutch, generally in a new nest.

The young birds are precocial upon hatching: downy and mobile with open eyes. Both parents feed them small aquatic invertebrates initially, then small fish for 38–48 days. Parents will perform distraction displays to lure predators away from the nest and young. Ornithologists disagree as to whether adults carry young on their backs while swimming with some maintaining that they do and others the opposite.

In the wild, the oldest known red-throated loon lived for more than two decades; it was found, oiled and dead, on a beach in Sweden 23 years and 7 months after it had been ringed.

Food

Like all members of its family, the red-throated loon is primarily a fish-eater, though it sometimes feeds on molluscs, crustaceans, frogs, aquatic invertebrates, insects, fish spawn or even plant material.