I have 9 barred rocks that are the oldest of my 33 chicks/chickens. The BRs are 16 months old. Last week I noticed one of the BRs (Merida) in the nest box at night. Her comb was kind of pale and she seemed a little thin but otherwise okay. The next day when I was on my way home from work my husband told me when I got home to come to the coop. It was dusk and the other chickens had gone in but Merida was lying in the run. When he picked her up and set her on her feet she started walking. So he brought her to me and I noticed that the feathers just past her comb were missing and her comb had obviously been pecked a lot. Put her in the garage brooder for a couple of days. She seemed okay. Put her in a coop with 3 young silkies and a young frizzled Easter egger for a couple of days. She did okay but seemed to be keeping them from the food. So I put her in the main coop again and the other barred rocks immediately started attacking her. What could be the cause? She is now in a coop by herself.