Hi, I have a rhode island red chicken that we have had since spring of 2020. Just yesterday I noticed that this particular chicken Gertrude was pecking at the rear of the other chickens (I have four total). I'm not sure what the intention was as I noticed she ate a feather that was on the ground earlier in the day. She did this several times while I was out in the run. This morning when I woke I checked the camera that I have in the run to make sure their pop door had opened. Three of the chickens was up on their gym in the run all crowded together which is unusual. I told my son to go out and make sure there was nothing in the run that had frightened them up there as only Gertrude was on the floor of the run. He said as soon as one of the chickens on the roost got down on the run floor, Gertrude like a missile went right for the other chicken and picked at the butt of the other chicken. This is all new behavior as these chickens were bought together as day old chicks. They have previous to this all gotten along together with no bullying behavior. Nothing new has been added or changed to their coop or run other than I moved one of their waterers out into the run as it started freezing and I bought a heated pad to put it on. That was about three days ago. The run is 10X10 feet and they have access all day to the run and the coop which is 4X7 feet. I don't notice any wounds on their butts as they usually run away from her before she gets a good peck. Does anyone have any ideas as to why she is doing this and how to break the habit? Right now she is in a dog crate with food and water in the run. The other chickens can see her and she can see them. I really don't want to have to get rid of her.