I 1st saw this bird when it was asleep, and washed-out Surf Scoter was what came to mind, but there were several problems with this ID as well. Harlequin Duck was the next thing I thought of, and I tried for this for a while. The facial pattern isn't sharp enough, and the pale rear flanks and undertail don't fit. Finally, after seeing a little white at the undertail area, Long-tailed Duck started to cross my mind, and once it raised its head and I saw the stubby bill, it fit.

This is the darkest Long-tailed that I have seen, granted I've only seen maybe a dozen. This dark face on this presumed juvenile bird (though the flanks are pretty pale?) isn't shown very well in any of the North American field guides, except in National Geo on the plates of flying ducks. However, some of the European Guides, such as Birds of Europe (Mullarney, Svensson, Zettersrom, Grant) does show it, and the Waterfowl Guide in the Helm Series doesn't show it, but does discuss the variability of these birds. I didn't realize how dark these birds could look.

Ironically, this is the exact location I found the much whiter female-type Long-tailed Duck which is posted in this same gallery, a few days previously.