I've read this post with Great Interest... This is our first year with ducks, One Pekin hen, and One Runner/Mallard mix drake.... they are in a roofless enclosure approx 16'x16' on one end of our pond. (Our Pond is approx 70'x30' about 8' deep) There is a small shelter (old dog house) for them but they rarely if ever use it... they have a small grassy patch... they are in the water almost constantly!! we placed the feeder in the shelter for them to keep the feed somewhat dry... last few nights the water on the ducks end of the pond froze over, with just a small "puddle" that both ducks are happily doing laps in !! they plop up on the ice and tuck their heads under their wings and sleep in the sun... the pond has an aerator but it's in the center of the pond and the water doesn't circulate into the duck pen...so we are going to find a small submersible sump pump to help keep the ducks water open...
Wild Ducks roost, sleep and eat in the water ... All ducks have oil glands that they use to "Waterproof" thier feathers.. we have wild ducks, Mallards, Gadwells and Black Ducks, in the river during the coldest of temps.. I would be concerned about the smaller breeds keeping warm... but the bigger breeds should be fine..