I give them pedigree, the kind I give my dog... see, it helps them stay warmer, gives them a nice heat boost, plus, if I don't give it to them, they try to steal it from the dog, which is a bad idea, and gets them nipped at. I usually give all my birds (6 ducks and a goose) about a cup and a...
I live in the mountains of vermont, and it gets seriously cold here. My ducks do just fine in their uninsulated, plastic wrapped shed. I give them warm water in the morning, refresh it with cool water mid-day, and give them a handful of dog food and a bowl of warm water (not IN the water)...