I have 10 assorted hens, between the ages of 14 to 10 wks. Lately, one of the older EE chicks started missing feathers on her back, just above her tail feahers. No blood, but there is a patch about the size of a quarter. I think she is being picked on, but can't find the one who is doing it. Also, how do I treat the picked on hen? Thanks in advance for your help!