A common sight around the more northerly shores of the British Isles, the Common Eider is the largest duck in the northern hemisphere. The eider is particularly well adapted to cold-water environments; the insulating properties of eider down are iconic. The species is taxonomically interesting, with a range of well-marked subspecies reflecting the patterns of ice coverage during ancient glaciations, and these ducks have also provided the focus for a number of important behavioral studies, especially on feeding ecology and energy budgets.

Eiders have a long association with humans,...