Clangula hyemalis
A small, elegant diving duck with highly variable looks depending on sex and time of year. Several moults with transitional plumages. Males with long, pointed tail and pink banded bill in most plumages. Females with grey bill. In all plumages note: small head, steep forehead and short bill with high base. Wings always all dark (also underside). Only diving duck with dark wings and light body. Flies with wings hardly raised above horizontal plane on upstroke.
Very vocal and distinct. Male: a pleasant resonant melodic "ahh-aaooee" in a yodeling, breaking triad. Starting with an accented first note (ahh), then gliding from first through second and third note (-aaoooeee). Far carrying. Female: calls often, but less musical and distinct than male.
Wikipedia: map (se also Xeno-canto below)
Birdlife ecology
Sounds:Recorded by Ian Cruickshank,http://www.xeno-canto.org ,CC license
