Common eider

The common eider (Somateria mollissima), also known as St. Cuthbert's duck or Cuddy's duck, is a large sea-duck, measuring 50 to 71 cm in body length, found along the northern coasts of Europe, North America, and eastern Siberia. It breeds in Arctic and some northern temperate regions and winters farther south in temperate zones, where it often gathers in large flocks on coastal waters. It can reach flight speeds of up to 113 km/h.

The female builds the nest close to the sea and lines it with soft down plucked from her own breast. This eiderdown has long been collected for use in pillows and quilts, though in recent times it has largely been replaced by down from farmed geese or synthetic materials. Today, eiderdown products are rare and typically sold as luxury goods, but harvesting continues sustainably, as the down can be collected after the ducklings leave the nest without harming the birds.

Taxonomy: The common eider was formally named by Carl Linnaeus in 1758 in his *Systema Naturae*, where he placed it in the genus *Anas* with the binomial *Anas mollissima*. It now belongs to the genus *Somateria*, introduced in 1819 by English zoologist William Leach. The genus name comes from the Ancient Greek *sōma* (body) and *erion* (wool); the species name *mollissima* is Latin for "very soft." Both parts refer to its down feathers.

Subspecies: Six subspecies are recognized. *S. m. v-nigrum* breeds in northeast Asia and Alaska, wintering in the Bering Sea and Aleutian Islands. *S. m. borealis* breeds in northeast Canada, Greenland, and Iceland, wintering in the north Atlantic. *S. m. sedentaria* breeds in Hudson Bay and James Bay, Canada. *S. m. dresseri* breeds in southeast Canada and the northeast US, wintering around the northwest Atlantic. *S. m. faeroeensis* is endemic to the Faroe Islands. *S. m. mollissima* breeds in northwest Eurasia and locally in central Europe (Alpine lakes) and the northern Black Sea (Crimea), wintering in northwest and central Europe.

Description: The common eider is the largest of the four eider species, weighing 0.81 to 3.04 kg, with a wingspan of 80–110 cm. In the North Atlantic, 22 males averaged 2.21 kg, while 32 females averaged 1.92 kg. It is distinguished by its bulky shape and large, wedge-shaped bill. The male has striking black-and-white plumage and a green nape; the female is brown but can be identified by size and head shape. The male's display call is a strange, almost human-like "ah-ooo," while the female utters hoarse quacks. The species is often easily approached. Drakes of different subspecies vary slightly in bill color: the nominate *S. m. mollissima* has a yellowish-green bill; *S. m. dresseri* and the slightly smaller *S. m. faeroeensis* have greenish-grey bills; and the Arctic Atlantic *S. m. borealis* and Arctic Pacific *S. m. v-nigrum* have bright orange-yellow bills.

Ecology: This species dives for crustaceans and mollusks, favoring mussels. It swallows mussels whole, crushing the shells in its gizzard and excreting them. When eating a crab, it removes all claws and legs before consuming the body similarly. The common eider is abundant, with populations of about 1.5–2 million birds in both North America and Europe, and large but unknown numbers in eastern Siberia. Some populations are small and declining, notably the isolated Crimean group in the Black Sea, which numbers only about 700–1,100 pairs and is of conservation concern.

A famous colony of about 1,000 pairs nests annually on the Farne Islands in Northumberland, England. It has been claimed that these birds were the subject of one of the first bird protection laws and that the first wildlife preserve was established for them by Saint Cuthbert in 676, but this is unlikely. No mention of Cuthbert having an affinity with birds appears in documents until a story published about 500 years after his death, and those later tales do not involve habitat loss or modern conservation concepts. Because St. Cuthbert is the patron saint of Northumberland, the eider became the county's emblem bird, and the birds are still often called St. Cuthbert's ducks or Cuddy's ducks locally.

In landlocked Switzerland, a small population of about five pairs of this normally marine species has colonized some large lakes since 1988, enabled by the invasive freshwater zebra mussel, which resembles its natural diet. In Canada's Hudson Bay, important eider die-offs were observed in the 1990s by local populations due to rapidly changing ice flow patterns. The Canadian Wildlife Service has gathered updated population data, and preliminary results suggest a recovery. The common eider is the subject of the 2011 documentary *People of a Feather*, which examines the historical relationship between the Sanikiluaq community and eiders, along with aspects of their ecology. It is one of the species covered by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds.