Could be a number of things. Not enough protein in their diet, need more space, cannibalism. One things for sure you need to find out whats what. Once they start this behaviour the whole flock could start feeding each other feathers & its hard to get them to stop. If your feeding alot of treats I would quit the treats for awhile. Add more protein to their diet such as meat , some eggs , even some GBS which is 28 % protein. Don't overload them with protein just up their protein some. Free ranging the birds will really help.
Well, they are eating the chick grower stuff. I don't toss much stuff out there, and when I do, the hens get it and the chicks don't really get any of it at all. The space, they have a large pen and plenty of space to run around. I dont' think that is it either. do you think it is a dominance thing? she is the dominant one of the 3 amigos hehehe. I have different groups of chickens in this pen. they all get along, but they definitely keep to their groups most of the time. these 3 hang out together a lot. they are all easter eggers.
Some of the feather eating is normal, even my free range chicks eat all but wing flight feathers as they come off. They do not pull feathers off each other though. I wonder why since thought is protien of feathers is hard to digest.
I wonder if it has anything to do with the fact that she had really bad coccidiosis a monthish ago. perhaps she is deficient from that in some regard? she's still doing it right now, I can hear the commotion. ugh.