I've been looking all over, besides BYC (because of the board issues tonight). A few hens in the coop are missing their feathers on the back end above the tail. Our coop holds up to 24 birds, but we only have 12 in there. We checked the birds for mites, lice, etc and found none. We also spray the coop regularly. While out looking over the birds I saw the roo mount one of the hens, I could see where he was standing on her it looks like his feet may be causing the damage. There also looks like there may be some picking going on. Although we were not sure, we removed that roo from the coop. He is the largest of all our birds and also the most agressive. I just wanted to double check other peoples opinions. Here is a pic of the worst hen.