A couple of my chickens have lost their feathers on their tails. I thought it was just birds picking on each other. But now Ive noticed that a lot of them have feathers missing. At the base of the tail where the feathers are missing the skin is scaly looking and white with sore looking red patches. Their feathers are not too good looking either. IE some of the fibers are broken. I thought it was mites or fleas or something, however I cant find any. Any thoughts?