I have four chickens and noticed that one of them has lost feathers around her vent, about a 2-3 inch diameter. We checked for mites and didn't see any. Its not red or sore looking just kinda bald. she seems fine, but it has been real cold this week . there coop is filled with cedar chips for bedding and they do sit on their perches but I'm not sure how they sleep. Is there something I should be doing?