Two of my ducks have gone missing within about a week and a half. The first dissapeared and the only trace was tons of feathers on the ground. The second it left the body and very few feathers were on the ground. The neck didn't feel broken at all, and there were no bite marks or traces of blood. We have had no predator problem before and have only lost three ducks, a long time ago, and they were spaced months apart. What do you think is doing it?