I would watch that someone is pecking his feathers out. I have 1 that was picked on in that one spot--his name honestly as a chick was Baldie because he stood up in the incubator and shaved his head on the fan, seriously........ They did it worse when they were closer together, so try giving yours more space they they are not bored and pick feathers. If they have plenty of space, consider adding more protein to their diet. Or it could be a dominant male showing his dominance. Either way, Nustock is an ointment that is supposed to do wonders with feather growth. There may be some "bad tasting" ointments, too, but I don't know what they are called.