Did you figure out what this is? I have the same balding with 4 out of 6 hens, 9 months old. I don't have a roo. They are fed organic egg layer pellets, oyster shell, and veggie scraps( usually in a hanging ball, sunflower meats with yogurt or cottage cheese, all organic. I brought one hen into ICU (intensive chicken unit) because it looked like she was developing some raw spots and I was afraid the others would pick at her thinking it was blood. She loved her warm bath and didn't notice hydrogen peroxide and I put tiny bits of neosporin on the raw spots. I cleaned their coop twice, fresh bedding, didn't find mites and took 2 of them to the vet and she didn't find any either and commented on how lovely their feathers and health in general seemed to be, and she ran a fecal sample for worms and it was fine... so in other words, an expensive shrug about what it is. They have a sandbox with play sand and DE and I sprinkled a small amount of DE under fresh bedding ( I used to use aspen shavings, but the vet suggested I switch to pine to see). I haven't seen them pecking each other, but I have put a drop of oregano oil at the base of all of their tails to help discourage it. Our weather has been 62 one day and 10 the next and lots of rain. They are all eating and drinking. I added a teaspoon of vinegar to their water and couple drops of garlic oil on their scraps. They have one tiny 7watt red bulb night light with a cover in their coop... I'm afraid of night predators and was told this might ward them off. I still get 2-3 eggs/day.