I have a pekin hen, roughly 1 year old, who has black, watery poop. She has been like this for a week now and none of the others penned with her seem to have it. It is so bad that it is all over the feathers surrounding her butt (almost like pastey butt on a chick). However, her appetite and behavior are normal. Any ideas as to what this could be and what I can do for her?