We have a hen in our flock of 4 who picks at the bottoms of the other hens. She sneaks up from behind to do this and tries to pluck out the feathers from the other hens' bottoms. She pecks/plucks and runs. She seems very aggressive about this except for the fact that she is at the bottom of the pecking order -- so is chased off by the picked-at hen when she is caught. Has anyone seen this behavior before? What could be causing it or why would she do this? I have seen her her picking up feathers in the coop and eating them. She is fed the exact same diet as the other hens which is scratch and layer pellets. Our hens are all 20 weeks old, except for her -- she is about 16 weeks old and barely noticeably smaller than the others due to her age. None are laying yet. Help!