My ducks free-range on dry land all day. I am about to start housing them at night. While I realize I may have to bribe them indoors at night with food, I really don't want to feed them before bed because of the extra mess - and I don't mean spilled food. I plan to hang some sort of waterer inside their house. How much feed do ducks really need, and how often do I have to give them their Purina?