I made a feeder for my ducks that I put out when they free range. It is a 2 gallon pail that I cut holes out of sides about 2" up from bottom of pail. Then I used one of those water jugs for a water cooler to hold food and placed it upside down into pail so it auto feeds. It has worked great for...
I use a auto feeder because my ducks free ranged around our 1/2acre pond and spent most of their time foraging so that way there was not a lot of wasted food. But I do give treats manually.
I have a variety of brown egg layers at the moment. I did have some khaki Campbell ducks but unfortunately the neighbors dog got to them while free rangeing. I am currently trying to hatch some muscovy but it's harder than I thought.