RE: Do hawks eat ducks?
From your description I would say it was a Marsh hawk also sometimes called a Harrier. One of the worst avian predators is the great Horned owl. They will take a mallard sized duck a day if their territory includes a wetland with an ample supply of ducks. They will kill birds up to a Mute swan in size and also Canada geese. Larger birds like this they do not tackle normally but they can and will when they feel up to it.