The Common Eider, (Somateria mollissima) is a diving sea duck breeding in the Arctic and some temperate area of North America and Eurasia.  It winters south in large flocks. With the exception of the Muscovy Duck, it is the largest duck in North America.  They have evolved cooperative breeding, laying eggs in nests of relatives and sharing rearing of ducklings. Eiderdown is feathers the hen plucks to line the nest and is still harvested from nests when the ducklings leave.