The Canvasback is an North American duck related to the similar-looking Eurasian Common Pochard.
It is bigger than the Pochard with a longer neck, -- surprisingly long for a duck, a more angular head and all black bill. Both drakes have red eyes.
Female Canvasbacks, above, have brown eyes and plainer plumage, also similar to a large, long-necked, female Common Pochard.
The ducks shown immediately above and all below, photographed in London, have mixed heritage;
all but one of the drakes shown have a tiny patch of blue on their black bills, betraying hybridism with the Pochard.
The female is similar to a large female Pochard with all-black bill. The small blue spot on the bills above indicates a Canvasback/Pochard hybrid.
More of the Common Pochard hybrid female (not Canvasback); other parent unknown. (Long black angular bill reminiscent of Canvasback.)