I rescued 3 chickens from a farmer who no longer wanted his animals. That was just before Easter, so mid April. I never had chickens prior to that. They came with their coop. It was pretty obvious that they were not used to people, and I was pretty sure they had never been out of the coop. I have no idea how old they are, but they were definitely not young. Also, were visibly not well cared for. After a couple of weeks, one died in the coop. Not sure how/why. We got chicks & eventually I started letting these 2 adults free range. They started to look healthier & while they still don't run to me like the "babies" do, they will take treats out of my hand. None of the 3 I adopted ever had feathers on their butts. I thought it was due to malnourishment or stress- like a prolonged molt. I added vitamins to their feed, give them treats on the weekends, supplemented their feed with feather fixer & game bird/ show bird feed, & they free range all day every day. About a month or so ago, the skinny one, Bertha, FINALLY grew butt & tail feathers! She looks beautiful. Percy, the fat one, has only just begun to grow feathers on her butt- but she picks at them sometimes. I figured they must be itchy. These chickens' coop has been cleaned & dusted for mites. I have never seen a bug on either of them. Yesterday morning I woke to find Percy's butt covered in fresh red blood. It was from a tail feather that had been ripped out. I saw Bertha peck at it several times before I could get Percy out of the coop, I washed it off & treated it with a tea tree oil spray and with a blue lotion (I think called peck no more?). I culled her overnight. She appeared to be fine & happy & free ranged alone all day. I let Bertha out with her briefly & they were fine. As soon as they went in the coop for the night, Bertha started pecking Percy's butt again. I am culling Percy again tonight. Now I'm wondering if Bertha has been pecking at Percy all of this time. If that is the case, will I ever be able to stop it? They both eat an excellent diet and have several acres to roam every day. I wouldn't imagine that it could be boredom at this point- only a habit. Like I said, I have no idea how old they are or how long this could've possibly been going on. Does anyone have any experience with this? Any ideas? I don't want to keep Bertha in the coop by herself all winter, but she bullies all of my other chickens, and I definitely don't want her to introduce this behavior to them as well. ^this was probably in June. You can see neither has many butt feathers^ Percy is on the left in both pictures above. Berthas feathers starting to come in. Bertha has tail feathers. Percy still doesn't. Bloody butt. Purple butt.