Two days ago I happened upon about a dozen Buffleheads involved in their annual courtship rituals at the refuge. Male Buffeheads court their future mates by a vigorous exercise of head bobbing, diving, running on water, and flying over the head of the female ducks.
Sometimes, a female Bufflehead chased a male away.
The courtship also took place underwater, perhaps with the males trying to prove they could be good foragers. I saw them dive and spend a minute or two submerged, but unfortunately was not equipped to take photos under water.