We currently have 6 RIR, one Rooster and three other unknown breed hens. Recently one of the RIR was found almost pecked to death. We isolated her and took care of her wound. Her back head feathers were plucked completely off. We have kept her isolated from the other hens and rooster. One time we decided to let her free range with the others and two of the hens charged at her and started attacking her. We decided to keep her away from them and partitioned a small area in the chicken run for her. The other hens are on the other side and when the injured hen (Rhonda) gets too close to the fence they still try to attack her, and more especially the rooster. Lately we have noticed that another Red has been bullied by the Rooster. She runs away from him and gets up as high as she can to get away from him. He doesn't mess with the other hens, just her. Today as my husband was checking on them he noticed that the red hen was inside the nesting box which was very unusual. He had a flashlight on her and saw that she was bleeding from her comb. Looks like the rooster or the other hens tore off part of her comb. My question is why are they picking on her and what should we do? Cull the rooster or isolate him from the rest of the flock. We have separated the hen and have put her with the other injured hen Rhonda in the chicken coop. We need advice.