I have 5 chickens (RIR, Ameraucana, GL Wyandotte, Light Brahma and Barred Rock) that are about 1.5 years old. I bought them all together as cute little baby chicks and they have always been together. Last summer a few of them ganged up on my Ameraucana and plucked a spot off her back, but then left her alone after a day or two of this treatment. It also wasn't particularly violent, just grabbing a beak full of feathers as she walked by. Starting about 5 days ago, my Wyandotte and Ameraucana have decided they HATE my Barred Rock. They chase her down, pin her to the ground and viciously peck and scratch her. She's been doing an okay job evading them and hiding, so I've been trying to let them work out their issues. This morning, however, I noticed that the spot they have pecked her feathers away from on the back of her head now has a bloody spot about the size of a nickel. I tempted her to me with some sunflower seeds, examined it and treated it with the Blu-Kote I had on hand. She seems fine otherwise and I'm sure the wound looks worse than it is as I am not a fan of blood, but I figured it was time to consult the pros now that blood has been drawn. I do not think space is an issue. Their coop is sized for 12 chickens (we heard about "chicken math" before starting our flock) and it opens into their enclosed inner run that is about 8'x10' that has their food and water. In the mornings, we open the door to their outer run (~10'x40') that they have access to all day. The rest of the flock spends the day scratching around in the outer run, which gives the BR hen access to the food and water all day. She runs back into the coop and hides whenever the two bully chickens get close. They have obviously managed to catch her to give her the wound though. The RIR and Brahma are staying out of the chicken drama. They do not bother the BR and the BR does not run from them. What should I do?