Rowly, I have had excellent results with Rouens and Swedish Blues. They both are large non-flying domestic Mallard variants. We don't get very cold here, mid 20's at night in the "winter" so freezing is not an issue. I don't provide any winter shelter and they have done fine for 3 years. They are excellent foragers and on my 2 acre pond do an excellent job of weed control. When I used to live in the Northeast, domestic Mallard variants survived quite nicely in some snotty conditions. They are quite easy to raise from day old chicks that are available by mail. Having an island for refuge will cut down on predation. You will still probably lose one now and then to a Great Horned Owl, Racoon, feral cat etc. Although they will lay eggs and attempt to brood them, the chances of any surviving are slim. Racoons and skunks love the eggs and Bass love whatever happens to hatch. So, you may have to add some birds each year or collect some eggs and hatch them yourself, which is what I do.
Good Luck
Jim
