I am a newbie in growing hens and I have four 10 months old hens. I just noticed that my Black Laced Silver Wyandotte is losing feathers from behind her neck. The skin looks yellow (sorry the picture is the best I could take ... I will try to get a better one). She is active as usual. Since the ground is frozen, I have two trays of top soil for dust baths. The coop is clean and dry. What could it be? How can I help her?