Eiders are large seaducks in the genus Somateria. Steller’s Eider, despite its name, is in a different genus. The three extant species all breed in the cooler latitudes of the Northern hemisphere. Two undescribed species are known from fossils, one from Middle Oligocene rocks in Kazakhstan and another from the Late Miocene or Early Pliocene of Lee Creek Mine, USA. The former may not actually belong into this genus.
The plumage of the Common Eider varies considerably. It passes through several stages while the bird is growing to maturity, and after the bird reaches adulthood at about three years old, the plumage alternates between two colours each year as a result of moulting, or the replacement of old feathers with new. In addition, the male’s plumage differs from the female’s.
Between the ages of three weeks and three years, male Common Eiders moult their feathers eight times, changing their colour from a juvenile blackish brown to an adult olive-brown and white in winter and a striking black and white, with a small area of light emerald green on the back and sides of the head, during the breeding season. Changes in female plumage are less dramatic: from a juvenile blackish brown, the duck becomes rusty-to-tan. The female’s summer colours provide good camouflage in the vegetation and rocks of the offshore islands on which she breeds.
Common Eiders can live 20 years, one of the longest lifespans among sea ducks. However, the expected lifespan for eider populations which are heavily harvested may be much shorter.
Listen to the sound of Eider
Copyright remark: Most sounds derived from xeno-canto
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The seven races of Common Eiders have different breeding ranges. In North America the southern race Somateria mollissima dresseri breeds from Maine to Hamilton Inlet on the Labrador coast; the northern race Somateria mollissima borealis breeds from northern Labrador to Ellesmere Island in the eastern Canadian Arctic; the Hudson Bay race Somateria mollissima sedentaria remains all year within Hudson Bay; and the Pacific race Somateria mollissima v-nigra breeds from Coronation Gulf in the MacKenzie District of the Northwest Territories to the south side of the Alaskan peninsula. Three subspecies are found outside North America: one in northwest Europe, one in Iceland and a third in the Faeroe Islands north of Great Britain.
The Common Eider belongs to the sea duck tribe (Mergini), which contains closely related ducks, all of which use marine habitats to some degree. The King Eider Somateria spectabilis, Spectacled Eider Somateria fischeri, and Common Eider all belong to the same genus, and hybridization is known to occur between Common and King Eiders.
Eider ducks are gregarious, travelling and feeding in flocks numbering from tens to thousands.
Some female eiders may breed in their second year of life, but males do not breed until they are three years old. Many females will not breed in some years. Common Eiders breed mainly on small offshore marine islands or isolated spits and points that are free of mammalian predators. Within a couple of weeks of arriving at the breeding grounds, the birds make prospecting flights and visits to choose a suitable nesting place. Often females will use the same nesting site for a number of years, while others choose new nest sites each year. They nest in early summer in dense colonies of tens to 10 000 or more; nesting starts progressively later as one proceeds farther north. There is one brood per season.
Only the female prepares the nest. In some races, the male stays with the female for a while; in others, he does not. When he remains, the male defends the female from other eiders and from gulls and ensures that she does not mate with other males.
The female begins laying the eggs a couple of days after the nest is ready. There are usually four or five eggs per nest, and generally, one egg is laid per day. When the second or third egg has been laid, the female lines her nest with down plucked from her body. While laying the egges, some females will leave the nesting colony, possibly to feed before they return to the nest to incubate, or sit on the eggs, continuously. Once incubation begins, the female only leaves the nest for a little as five minutes every two or three days to drink, but not to eat. During early egg-laying, if the male is still in the vicinity, he accompanies the female on her breaks. By mid-incubation, most males have left the colony on their moult migrations. Incubation lasts from 21 to 24 days, and about 50 to 70 percent of the eggs hatch successfully.
The downy newborns leave the nest within 24 hours, and they feed themselves. Within one hour of entering the water, they can dive competently. Young first fly when they are 60 days old. Generally, few survive to fly; many are lost to predators, exposure, or starvation in their first week of life. In good years, one duckling per adult pair may survive for the fall flight. On the other hand, adults are often long-lived, and estimated annual survival rates vary from 80 to 95 percent. This low reproductive success, which is compensated by high adult survival, is very characteristic of eiders and other sea ducks such as scoters and Long-tailed Ducks. Most other ducks breed more successfully but lose 40 to 50 percent of adults each year.
The mother’s relationship with her ducklings ends when she leaves for the moult migration in the autumn. In the fall migration, groups of young may travel together and arrive before the adults on the winter range.
In winter, when daylight is short, more than half the daytime hours are spent in feeding. The ducks feed in shoal waters off headlands and offshore islands and skerries. Flocks move together at the same rate, the ducks at the front of a flock diving first and the rest following sequentially. After 15 to 30 minutes of intensive feeding, flocks move offshore to rest, preen, and digest the contents of the gullet. The feeding sequence is then repeated.
During spring migration, and when the eider ducks arrive near their breeding places, much time is spent feeding, and the birds accumulate fat. These stores are particularly important for the breeding females, or hens, which rely on the reserves through the incubation period. Unlike many ducks, the hen does not feed once she starts sitting on her eggs.
The young apparently eat insects during their first week of life.
This mainly marine species is breeding on arctic islands, in the north-west and extreme east of Eurasia and in North America. Some populations are sedentary. Others are migratory, wintering mainly in Denmark, northern Germany and the Netherlands, but reaching the Atlantic coasts of France. A few birds are seen in Central Europe and the western Mediterranean. The population of north-western Europe is totalling 1.7 to 2.3 millions of individuals (Scott & Rose). A few birds also reach Greece. They probably belong to a small population inhabiting the Ukrainian shores of the Black Sea
Breeding populations of south-east Europe mainly sedentary, flocking in winter, moving only if bad weather. Those breeding Volga area and Ural steppes migrate to Caspian, where join resident breeders. South of main wintering areas, small numbers occur fairly regularly Iberia, Mediterranean basin east to Nile valley and Middle East.