I hope this is the right place to post this question. I have a beautiful white and salmon colored Easter Egger named Birdie. By all evident measures, Birdie is very healthy. She's a good weight and she eats and drinks well. She's active and curious, and she routinely lays 5-6 pretty blue eggs each week. However, starting several weeks ago, I've noticed that her hind end is filthy all the time. Here's a photo I snapped of her walking away from me so you can see what I mean. I keep a scrupulously clean coop and run, including nest boxes, and Birdie is also allowed plenty of free range time in our fenced backyard. Yet her bum remains super dirty. I have one other white chicken, a Silkie, and she is never dirty like that around her vent and hindquarters. I'm worried that something is wrong with Birdie that I'm not aware of, and so I can't address it. Any ideas as to what could be causing her to remain filthy in her tail area like that? Many thanks.