I noticed it yesterday, one of my 18 week old Wellies is picking out her neck feathers under her chin. Then she was gaping so I thought it could be in reaction to crop distress. I massaged her crop and it feels hard but I can't say it feels unusual. Is it possible that she has eaten too much of the granite grit I recently put out? My chickens have a large yard but most of it is grass covered so I put out some grit just in case.