My six hens have been together since day 1. Once they were out of the brooder into their new coop they roosted together. Lately when I have gone out to lock them up I noticed they havent been letting their sister up on the highest roosting bar. I keep putting her up on the top because it is getting chillier at night and I dont want here to freeze. She doesnt appear to be sick. She is still laying, eating and free ranging. She has always had a lighter red comb than the rest on one side so I dont know if that causes a problem or not.