How old were they? Were they in a secure coop where even tiny predators could not squeeze through? Weasels can get through 1 inch chicken wire or the tiniest hole. What did the bodies look like and where were they located? Can you look at their feed to note if there is any off odor or mold? If you have the bodies, you can refrigerate them and get a necropsy by your state vet. Sorry for your loss.