I have 12 hens (no rooster). They all live in a 8'X12' unheated coop.and have not been out much because of the weather(Northern Pa.) Everyone seems to be healthy and productive (they are nine months old). I noticed yesterday that one of the RIR's had a round bare spot about 3" in diameter just below her vent. She is acting normal. I am clueless on this...can anyone help?