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.

The common eider was formally named by the Swedish naturalist Carl Linnaeus in 1758 in the tenth edition of his Systema Naturae.

[6] Six subspecies are recognised:[5] The common eider is both the largest of the four eider species and the largest duck found in Europe, and is exceeded in North America only by smatterings of the Muscovy duck, which only reaches North America in a wild state in southernmost Texas (and arguably south Florida where feral but non-native populations reside).

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.

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).

In Canada's Hudson Bay, important eider die-offs were observed in the 1990s by local populations due to quickly changing ice flow patterns.

This can lead to a high degree of relatedness between individuals nesting on the same island, as well as the development of kin-based female social structures.

Examples of these behaviours include laying eggs in the nests of related individuals[17] and crèching, where female eiders team up and share the work of rearing ducklings.