The Odd Couple of Ducks

As I stood on the bridge, a pair of mergansers shot from underneath it, borne by the main current of the Ottauquechee, down some from past days, yet still flowing well.  They are an odd male/female combination.  The male has a black head and black top to his frame, while the rest, at least while swimming, is pure white.  The female seems mostly brown, with a tuft of feathers pointing backwards, like hair in a hurricane.  They do not look like they belong together.  They rode the fastest part of the river, traversing from left to right with the flow, the female behind the male by a foot or two, until they entered the rippled white water around the bend and sped out of sight.