The latest edition of the BTO's journal Bird Study includes the following paper: Subspecies status of Common Eiders Somateria mollissima in Shetland based on morphology and DNA by Robert W. Furness, Barbara Mable, Fiona Savory, Kate Griffiths, Stephen R. Baillie and Martin Heubeck.
Using DNA from specimens of Eider found dead in Shetland, and biometric data collected from a cannon-netted sample ringed in the 1980s, it is concluded that Shetland Eiders are closely similar to birds from the Faroe Islands, subspecies faeroeensis , and distinct from the nominate mollissima to which all Scottish Eiders
have been conventionally assigned.
Interestingly, Eiders from southern Iceland are more similar to faeroeensis according to DNA, despite differing in plumage and being assigned to a different subspecies borealis. As has been suspected for a while, they conclude that the taxonomy of the Common Eider group may be in need of revision.
The allocation of the Shetland Eider population to a new taxon, found nowhere else in the UK, has clear implications in conservation terms, especially as the population is in long-term decline.