Q: My flock is pecking one another! What should I do?
A: Pecking, also called picking, is almost always the result of high stress levels. When that happens, the birds will sometimes pluck each others' feathers out, and can really hurt one another. Those lowest in the pecking order may have bare spots on their backs or their heads.
Here, feathers have started to re-grow on a bare back.
Many "experts" recommend you de-beak birds with this behavior problem (trim the pointy end of their beaks so they can't injure one another), but we don't. BAD idea! First of all, it's cruel, because it prevents the birds from preening naturally, and from being able to properly forage for small bugs and tasty plants, since they can no longer perform precision pick ups with the tips of their beaks. It can be painful, too, and that will absolutely increase their stress levels. Lastly, it only addresses the symptoms (picking) but not the underlying problem (stress).
Happy chickens don't pick one another! So, to deal with this problem, you have to figure out why they're not happy. Do they have sufficient space? Are there enough feed and water containers to go around? Are there enough nesting boxes? Could they have worms, lice or other parasites? Sometimes even a nutritional deficiency--not enough protein!--will cause them to try eating feathers in an attempt to get what they need for their bodies. Make sure they have plenty of good, high protein layer feed--NOT scratch. (Scratch is too low protein; a diet high is scratch/corn is likely to cause picking.)
Try buying a higher protein feed to see if that helps. Try letting your chickens free range, and see if that solves it. Check for mites, lice and worms. Give them additional feeder space so they don't have to compete for food. Make sure you are letting them eat free choice--don't restrict the amount of food they get every day, or only those highest on the pecking order will get to eat. Talk to your vet if you can't figure out what's going on. If you don't take care of the problem, you run the risk of escalation to the point of cannibalism (seriously).
While you are solving your mystery, it would be a good idea to purchase or make a saddle or apron to help protect your hen's bare spot and give her time to heal. These products also prevent the type of feather loss due to excessive mating.