The common eider is a master of survival that turns invasive species into dinner

Nature · Published 3 October 2026 Swipe more like this →

In short: The common eider is the largest sea duck in the Northern Hemisphere, famous for the insulating down that lines its nest. While typically a marine bird, this resilient species has adapted to inland life by feasting on invasive mussels, proving that even strict specialists can thrive in changing environments.

The common eider, or Somateria mollissima, is a heavy-set sea duck measuring up to 71 cm in length. Named by Carl Linnaeus in 1758, its genus name reflects its unique biology: Somateria combines the Greek words for 'body' and 'wool,' a nod to the exceptionally soft down feathers females pluck from their breasts to line their nests. This down, once a staple for luxury quilts, is still harvested sustainably after ducklings depart, as the process causes no harm to the birds.

These ducks are highly specialized predators, diving to depths to swallow mussels whole, which are then crushed within their gizzards. While they are strictly marine birds by nature, they demonstrate remarkable behavioral flexibility. In Switzerland, for example, a small population has successfully colonized large lakes since 1988, sustained entirely by the presence of invasive zebra mussels. This ability to exploit new food sources highlights their adaptability, even as some populations face threats from shifting ice patterns in regions like Canada's Hudson Bay.

Socially, eiders are colonial breeders that exhibit strong natal philopatry, with females frequently returning to their birthplace to nest. This behavior fosters close-knit, kin-based social structures, which researchers believe may have driven the evolution of cooperative breeding. In these colonies, which can range from fewer than 100 to over 15,000 individuals, females may share the labor of rearing ducklings through a practice known as crèching. Despite their abundance—with millions of birds across North America and Europe—certain isolated groups, such as those in the Black Sea, remain of significant conservation concern.

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