Feather picking is usually considered due to too little protein, too little space, boredom, or a combination of the above. I would say it's normal for a chicken to pull a feather occasionally, but you shouldn't see it very often, and you shouldn't see bare spots. Some people give so many non-protein treats that they end up reducing the chickens' total protein intake by accident. If they live in a small space, sometimes adding a hiding place or an extra roost will help a bit. Flock block type treats or a hanging cabbage that they can work on for a while are another approach (you can make your own.)
