Canvasback
Aythya valisineria

I keep running into canvasbacks in the same spots every year, and every year I think I’ve worked them out. I haven’t.
In my experience, sex differences show up more reliably in the field than any field guide suggests; the plates always look cleaner than the bird.
Regional occurrence notes: I usually catch this species in the north america part of its range.
One winter I had a pair stay on the same river bend from November into late March and I wasn’t sick of them at the end.
Anyway: not a rare bird, not a hard bird, but one I want on every trip.