HELP !! I have one of 5 of my hens that is acting wierd.. usually a friendly bird, she has been sitting in the nest box for 2+ days... I take her out and she goes back in... I was checking her today and notices that her breast bone area is bear ... when she puts up her "tail" bald there too .no feathers.. BUT no sores either... these are my first chickens.. they are about 6 months old... WHAT's going on ???