So, I have eleven 15-week old chickens with a 6 older hens. They been together for several weeks and everything has been fine. A bit of aggression, but that's normal. However, a couple days ago, I noticed that one of my Partridge rock pullets looked like she was missing neck feathers. I ignored it at first, but now it just looks odd. She walks around looking like a rooster about to attack, her feathers all up. Now, I'm not sure if she's missing feathers or they're all flattened, but she's totally fine except for that. Is it caused by the other hens, or possibly even a couple of the cockerels? Please help, how can I deal with it?