I'm assuming it's because she's bored. They free range normally, but have refused to come out of their coop for days because of the snow. It is a very large coop, and there are only 6 of them, so crowding is not the issue. So a couple days ago, I noticed in the morning, one was following another around picking at her fluffy butt feathers. By the end of the day, that one was totally bald on her butt! So the next day, I stuck the trouble-maker and a friend under the deck so they could be out of the snow, but not in the coop. This morning, the one was back to feather plucking, so I put her and a friend out under the deck again. But we keep getting more snow! Does anyone have ideas other than separating them like this every day?