Whenever you introduce new chickens to an already established flock, you run into this. It's normal, however; you need to keep an eye on them daily. They can peck the new ones to death. It should work itself out within a couple of days. I had that happen to me and I feel sure they would have eventually made the one they were picking on so weak she wouldn't have survived it. My chickens are my pets so I removed her and got her a new friend a built a new coop for them seperately. Both coops live in harmony now.

I have had my chickens for a year and a half now and also have a poultry enthusiast club. Email me anytime!
cherrychickens@gmail.com