That looks very similar to my roosters butt right now. He is about 10 months old, and started losing tail-feathers last week. I had to remove him from the flock because the girls were pecking him terribly. I kept him in for about 3 days and then applied Blue Kote. Unfortunately, the day after his return to the coop, they were at him again. I don't know why the Blue Kote didn't deter them, but I have him in a cage in the house right now. Does anyone have any other suggestions or an idea about how long I should keep him separated? Also, I am wondering why they're doing this to him, yet they don't do the same to each other... (3 of them are Golden Comets I got at auction; they're older and 2 have been molting...)?