Wood Duck x Pintail (Northern Pintail) Aix sponsa x Anas acuta
This duck stumped me! It seemed to have features of Mallard and of Wood Duck, but is quite different from photos of Mallard x Wood Duck hybrids (especially the bill) so I didn't think that coiuld be the correct ID. Various other species came into the frame for me, including Pintail, Wigeon, Teal and Aythya sp. but no combination seemed to explain everything. Thanks to Joern, Carl Gunnar and Lars for their insight into this ID conundrum - I don't think it's fully resolved yet but if it's not a trigen then the favourite ID seems to be intersex Wood Duck x Northern Pintail.
unidentified hybrid duck, possibly intersex Wood Duck x Pintail, Holkham Park (Norfolk, UK), 4th February 2012