I'm still having a suspicion that they're scooting under a fence or doing something to wear those feathers out faster... I have 2 BRs that like to dig out of the run, and they squirm under the fence when they do it. The damage is on their shoulders and tails from dragging under the fence.
But...
I've had that happen to my hens that roost on the top bar in the coop. It was because their tails were rubbing the wall ;)
Is it ALL feathers, or are they just in a certain area?
Do you have a rooster? They can tear feathers...
What feed do they get? Some BOSS van help keep feathers shiny...