This Common Merganser was foraging in the Willamette River below our house. It is probably a female, but I can’t be sure since the males change their feathers this time of year and look a lot like the females. I suppose this is similar to what male mallards do, though it may be for different reasons.
Mergansers are diving ducks, which means they dive into the water looking for food. When they dive, all they leave remaining on the surface are ripples like these.