If you notice the lack of feathers and baldness on the back of her head, that is from a roo, usually. Also, the saddle area missing feathers is typically a roo. However, once the bareness starts, of course all the other hens pluck at the redness, too. A friend of mine who has raised chickens for years (she is in her 80's) SWEARS by putting Vaseline on any bare exposed skin. She says it helps the skin to heal, and the chickens won't peck it because they don't like it on their beaks. Of course, here in Texas I worry about sunburn from the Vaseline. But she says it's the best thing to stop pecking chickens and heal the area. Also, Apple Cider Vinegar in their water (2 to 4 tablespoons per gallon of water) promotes good feather growth and good health.