About hawks...yes, the bigger ones will eat your ducks if they want to. So will eagles. And owls, if your ducks are out at night.
Right now my juveniles go out int he backyard during the day. Its fenced but not covered. They are learning to take naps under the hammock instead of out in the open which makes me feel a lot better about their safety. We also have been cultivating the good will of a medium size group of crows. Between them and the swallows no hawk or eagle has been left unmolested when flying over our airspace. The sheer number of things that can cause death and mayhem to a group of ducks is enough to give a person heart palpitations.