Duck eggs are more nutritious and much easier to produce without  outside inputs. You can almost get away with feeding them cooked potatoes, corn, and cooked squash if they have ample forage opportunities. Chickens which I love are just not great foragers. 

 Sorry if I’m going on, just thinking out loud. I wonder how much space you would need for perennial wheat to feed the ducks. I know chimacum grainery grows it. But probably too much of a pain to harvest thresh and sift. 

 Great question