Im new to being a chicken owner and have had my flock since august/October. Up until 2 weeks ago everything was paradise. My chickens were allowed free range while I was home and in the pen when I wasn't. I've lost two hens in two weeks due to eagles, so I've not allowed my chickens to be free in the yard since. The size of the pen not including the coop is 40x16 with 1/3 of it separated for my 11 week old chicks that I bring out into the yard during the day. Today I caught my Americana hen going after my RIR hen. I separated them for a while and thought everything was ok and then I saw the rooster going after the RIR. Separated het from them for awhile and then put them back together after a while. Well a neighbor came over to being them some fresh vegetables and mentioned the rooster wouldn't leave my RIR along thinking they were loving one another. I found the RIR in the coop with the rooster and the americana hen on top of her. Once I got them off of her she had been pecked to the point that there was blood on all sides of her comb, around her eyes, ears and feathers ripped out on her head and neck. I've put her in separate quarters for the night even though she was distressed to be separated from the flock. My questions is, what caused it in the first place? Initially my RIR was the head of the hens. I have a total of four hens and the rooster. The chicks live in the garage at night and I'll put them together when they are the same size A's the adults. Also, how can I keep them from attacking the RIR again once she heals? Im baffled, upset and not sure what to do. Can't understand how there was such peace and harmony and now all this. I've heard of other hens attacking each other but never a rooster. Up until today he was the kindest, loving rooster anyone could ask for. Please help me know what caused this, how to fix it and what to do to make sure it doesn't happen again. Thanks!