Canvasback Aythya valisineria
This North American species is an extremely rare vagrant to the UK. I saw the bird at Wissington Beet Factory in 1997 and then again when it reappeared at Welney in 1998, but I did not have a suitable camera back then. The only wild birds I've seen are a couple in Canada, including this muddy-faced bird.
Canvasback, Reifel Migratory Bird Sanctuary (British Columbia, Canada), 8th September 2006
The species is sometimes found in captivity as was the case with this one.
captive Canvasback, Blakeney Quayside collection (Norfolk, UK), 18th January 2004
captive Canvasback, Blakeney Quayside collection (Norfolk, UK), 7th November 2003