I've been told that they do it to recoup protein, but seeing as how only two in my flock do it, I don't know. They seem to put just about anything in their beaks, so it's hard to tell what motivates them. XD
Anyway, yes, mine do it. They love feathers. They eat all that they find (except for the flight feathers) and have been doing so for two months without issue.
Mine did that a lot before I started giving them a little extra protein. I started feeding them yogurt and/or hardboiled and mashed egg yolk. After a few days of that, they stopped. Now I give them extra protein every 3-4 days. Problem hasn't recurred.