I have five (various breed) hens in my yard. I got them from a backyard chicken person when they were 8 months old, and they're about 15 months old now. They have been in great shape until about a month ago, when one of them lost some feathers on the side of her neck. I thought she'd had an altercation or something. Then she apparently continued to lose feathers, because I would find them in the chicken coop. Today she seems to have lost all her feathers in a symmetrical pattern on her shoulders and the front of her neck, and is walking in a staggering, sometimes sideways gait. She is eating and foraging with the other girls, though. This afternoon she was shaking with cold, so I captured her and have her inside in a big dog carrier (with food and water). She has lots of new feathers coming in on the bald spots. I have many years of chicken experience, but I've never seen this before. They have no contact with other chickens. They forage in my fenced yard during the day, and spend the night in a coop with a run, fresh water, and layer crumbles in a raised feeder. Any ideas of what it is and how else I could help her? She's the smartest of my girls. Her name is Sharpie (my boys named her after the marker, because she's mostly black), and she may be part australorp.