I think this is a male Shoveler coming out of 'eclipse' plumage, which is the female-like plumage male ducks take when moulting their feathers at the end of summer. Apparently Shovelers can retain this plumage into winter - see the attached note on eclipse plumage from the US Wildlife Service
"Nearly all drakes lose their bright plumage after mating, and for a few weeks resemble females. This hen-like appearance is called the eclipse plumage. The return to breeding coloration varies in species and individuals of each species. Blue-winged teal and shovelers may retain the eclipse plumage until well into the winter"
This is why it appears half-way between a male and a female.
