There are feather shafts in the picture where they have not been broken off. Some chickens will pull out feathers of meeker hens, and sometimes while sitting on a roost. The biggest bump looks like where the preen gland is located. Feathers can become ingrown causing bumps. Mareks disease can sometimes cause skin lesions. You might try exploring one or more of the lesions with a sterilzed needle to see if there is pus or an ingrown feather inside. A hen saddle or apron may be tried to cover the bare area to see if the feathers will grow back in.