I have a few hens that are missing neck and back feathers and it's actually the rooster getting aggressive during breeding. He never did that until he got a month or so older. I also have a hen that plucks the feathers out of the hens lower in the pecking order but only when they are in her space.
Mine started back in the winter before I picked up the roo. It's been getting worse started with a few hens - now I have 13 out of 17 hens with missing back or tail feathers. Time to put a stop to it... You can read more about it here http://www.backyardchickens.com/t/1093526/rir-tail-feather-loss#post_16807692
Edited by crealbilly - 4/5/16 at 3:39pm