Very odd duck(?) with disc-shaped head

I saw this guy paddling along with a bunch of ordinary looking ducks, and I was boggled. What is it please please please?

is beautiful Hooded Merganser Drake

Thank you so much! What a stunning bird. I've been yearning for a 300mm lens, and my need today increased considerably. He was moving fast, and I had to run to get downstream, but never got any closer. Thanks again for your quick reply. I have some Facebook friends waiting breathlessly for my next post.

They are very leary in the wild. I used to hide behind a tree in areas here I saw them by the waters edge and wait for them to come closer to get pics.
Here is a short video of mine with the drakes doing their mating dance.These are legally purchased and I have Federal Permit to have them. http://www.youtube.com/watch?v=2A_N9nUAmJM

Thanks so much for the video. What fun it must be to spend time around them. I see Grebes sometimes in this area as well, so I consider myself blessed by the Birdwatching spirits.