Sibley has a brief explanation of the drab plumage I saw in male wood ducks at Gazzam Lake yesterday. It's called eclipse plumage and correlates with an early molt in which they are flightless from molting their flight feathers; they will molt again in the winter because that's when they pair up and they need the bright plumage for that. It's thought that eclipse plumage is worthwhile to male ducks despite the investment of energy in two rapid-succession molts because it's cryptic at a time when they are vulnerable because of their flightlessness. This was news to me and I thought it might be interesting.
Stephen Hubbard