Eiders are both migratory and residents in Iceland and very common along the coast. They feed on mussels, seasnails, crabs etc. which they swallow as a whole and then grind in their stomach. They also feed to some extent on sea weeds.
The common eider produces the eider down, which is harvested in colonies in protected areas by eider farmers. Eiders often nest in company with other birds, such as Arctic Terns. During the breeding period the female will stay on the nest, even when it is approached by humans. Once the chicks have hatched, the female leads the group immediately to the water where they are safer. In order to offer protection from predators (Gull, Skua etc.) the females with chicks form larger groups on the water.