Mallards and wood ducks are the two most common ducks to cross breed. Figures because they are both numerous. I find it interesting that most hybrids are infertile but about a quarter are not. Guess it depends on how closely related, how much common genetic material the parents have in common. There have been 400 hybrid combinations recorded according to DU so I expect most duck hunters have seen a hybrid but it was so minor a difference it went unnoticed.
Many years ago my late hunting partner came across a Gadwall hen with a broken wing shortly after seasons end. Being a doctor, a bit of an oddball some would say, he decided to amputate the bad wing, flap the surgical site, gave the girl an antibiotic and brought it home to nurse back to health. It ended up living several years on a small pond on his little farm. He said it raised several flocks of chicks which were all crossed with local mallards.
