I have two BR hens that are about 1 1/2 years old now and one of them has begun to lose feather off of her bottom. The other hen has a nice fluffy rear but this one looks like she has diarrea because the feathers are clumped together even though she seems to always go to the bathroom with rather firm poo. My grandfather said it could be mites and that I may need to spray her but I would think the other hen would have them also because they sleep in the same roost at night. Anyone have some ideas?