I have recently used DE (in the event mites or other parasites were causing this) on the ground, in the hen house and in the nesting boxes and I have added more protein to their diets. They are totally butt bare and also some are bare on their backs (saddle) before the tail feathers fan...
I am so glad to see your bare butt Girl. I have been frantically reading so many posts trying to learn about their molts. Neck, backs, yes, but mine have never had butt molt before. I'm relieved to see that it is not abnormal, or something I'm doing wrong. It looks so bad and so sad...