I've read several similar questions here, but I'm curious if anyone can give me some insight. My chickens are all about 8 or 9 months old, so they are not molting. One of the hens, a silver-laced wyandotte, has lost most of her neck feathers, though the quills are still there. I see no sign of mites or lice, and I've never noticed any aggression from the other 5 hens. Is there any other possibility I'm not thinking of? She seems perfectly healthy otherwise. Thanks in advance!