I have 6 chicks 16 weeks old they have all been healthy until now. I noticed last week my nicest chick Judy,a buff orphington, had something red behind her ears. Upon further inspection i noticed the feathers were gone . She has been acting normal and sweet like always. She is the bottom of the pecking order and my other BO pecks her if she gets too close to the food. This morning I notice sparse feathers in the same area on my 2 RIRs and the orhter BO. It is not red but just looks likes the feathers are thinnning out. My 2 EE don't have any sigs of this. They are acting normal. What is wrong and what do I need to do?