When I opened the coop this morning one of our new hens was on her back on the floor dead. She was perfectly fine last night as we do a head count and check them all before locking the coop for the night. Everyone else seems fine, and I don't see any visible injuries, although the ladder to the nesting box was busted off and lying near her. Could a simple fall have killed her? It's only about 2 feet off the ground.