The Common Eider (Somateria mollissima) is a large (35-45 cm body length) sea-duck, which is distributed over the northern coasts of Europe, North America and eastern Siberia. It breeds in Arctic and some northern temperate regions, but winters somewhat farther south in temperate zones, when it can form large flocks on coastal waters.

The eider's nest is built close to the sea and is lined with the celebrated eiderdown, plucked from the female's breast. This soft and warm lining has long been harvested for filling pillows and quilts, but in more recent years has been largely replaced by down from domestic farm-geese and synthetic alternatives. Nonetheless, eiderdown harvesting continues and is sustainable, as it can be done after the ducklings leave the nest with no harm to the birds.



The Common Eider is characterized by its bulky shape and large wedge-shaped bill. The male is unmistakable with its black and white plumage and green nape. The female is a brown bird, but can still be readily distinguished from all ducks, except other eider-species, on the basis of size and head shape. This duck's call is a pleasant "ah-ooo", described as being "like a bunch of gossipy old women, expressing surprise". The species is often readily approachable.

Drakes of the European, eastern North American and Asia/western North American races can be distinguished by minor differences in plumage and bill color.

This species dives for crustaceans and molluscs, with mussels being a favored food.

It is abundant, with populations of about 1.5-2 million birds in both North America and Europe, and also large but unknown numbers in eastern Siberia (HBW).

A particularly famous colony of eiders lives on the Farne Islands in Northumberland, Britain. These birds were the subject of one of the first ever bird protection laws, established by Saint Cuthbert in the year 676. About 1,000 pairs still nest there every year. Because St. Cuthbert is the patron saint of Northumberland, it was natural that the eider should be chosen as the county's emblem bird; the birds are still often called Cuddy's ducks in the area, "Cuddy" being the familiar form of "Cuthbert".

The Common Eider is one of the species to which the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA) applies.