http://www.birdpix.nl/album_page.php?pic_id=84086 (http://www.birdpix.nl/album_page.php?pic_id=84086)
I Think the left bird has some genes from Aythya nyroca, but is unlikely to be a first generation hybrid.
I´d think this could be a backcross of a hybrid ferina x nyroca to a ferina.
Can you rule out a backcross of a hybrid Tufted Duck x Common Pochard to Common Pochard? With the pure black breast and undertail coverts, I don't see much of a Ferruginous Duck in this bird.
No , I can´t ...
but on my monitor the eye looks more whitish than yellow and the head is a deep reddish-brown, and the head has this very peaked appearance...
That´s why my first thoughts were this bird involves A.nyroca genes...