This bird was swimming with 4 Common Eiders on Duxbury Bay and was seen just once (I had only 5 minutes – it didn’t fly) and is recorded in these photos pending identification. Based on head shape and overall giss I guessed it was a partially leucistic 1st year King Eider with a darker than normal bill. Thought possibly it might be a Surf Scoter with somewhat aberrant plumage (relative to books I have available) as it has a similar flat head and look and is supposed to have white on the head (though in a different pattern). I see numerous scoters and eiders during the winter, and here the tendency I note is for the very uncommon to rare King Eider to stay close to Common Eiders (as this bird was doing even when scoters were nearby). At this point, my overall impression led me to leucistic King Eider (note: An unmistakable adult male King Eider has been present since about a mile from this location since at least April 7).
I will route these pix to more experienced birders for their thoughts and update this gallery when I have more inputs to share.

I routed the photo to other more experience birders and have received word that it is a Surf Scoter.