A couple months ago I got a new, mean hen who terrorized my other two hens. They have since settled into an uneasy truce, with my first two hens avoiding the other as much as possible. At night when they go into the chicken house, the mean hen roosts, while the other two stay huddled on the floor underneath her. This doesn't seem healthy for them, and I worry that when it gets really cold, all three will need to stay together for warmth. Is there anything I can or should do to get these two hens to roost again?