Does anyone know what this duck is???

ducks in water.
Here is its size relative to the tame mallards in the pond (on the El Macero golf course in Davis).
duck.   duck.   duck.
It looks a lot like a bird we saw at a hotel in Hawaii — which I was told was a "RED-HEADED POUCHARD". But that one's not in my field guide, so I can't confirm it. Any suggestions would be appreciated.

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