One of my coops has six pullets who have been together since I brought them home last spring. All was well until about earlier this winter. I now have six bare-butt girls. When the first lost her back-end feathers and was bleeding, I thought it was a medical issue and took Lucille to the vet to make sure it wasn't illness or parasites. Nope.
The girls -- who all fancy the same nest box -- all lay with their heads against the back of the box and their butts exposed toward the center of the coop. Although it's not the only nest box, it's the only one they want to use. Often, two girls will try to wedge into the same box, leaving their backends as targets for whoever is in line next.
I agree, boredom may also have played a role. There were two serious blizzards in January, where it was impossible for them to go into their run. Now, with spring-like weather, the girls are out and about with the rest of the coops' residents, and I can see feathers coming back in.
Initially, I was applying Vetericyn to the featherless backsides daily. Lucille also got antibiotics because she was actually dripping blood from her wounded butt.
Hope you get your girls figured out!
