Does anyone know why my chickens would be getting bare spots on their stomach's/butts? I have one chicken with a lot of feathers missing and another that is looking similar but not as big a spot. The chickens were hatched in June and have been laying since December and seem healthy overall. I did not see any mites or missing feathers elsewhere on their bodies. The other two chickens seem unaffected. The vents are still feathered and look okay.