...especially mallard hybrids. It is all explained here, but even after that thorough explanation and gorgeous photos, could you always identify a mallard duck hybrid?
In Swedish, mallards are called 'gräsand', which means grass duck. Ni idea why, I guess they like grass.
(PS. It seems the Manky Mallard website is down right now (link above, so if it doesn't load, try again later.)