Hello everyone, I have something strange happening with one of my hens. She is two years old (not sure if age makes a difference) but I notice that her tail feathers have all come out and I noticed that her wing and butt feathers are thin and this morning I noticed what looked like grey stuff all around her top of head. She is active and runs around with the other girls and she is eating and drinking so Im not sure, should I be concern or is this normal? please help me understand