I have a mixed breed flock of 15 hens. For a month or so now I have noticed mild aggression by the rest of the flock toward one barred rock. The last day or two the aggression has become much more pronounced. Today I isolated the hen which has had feathers pecked and I suspect been pushed around aggressively for some time. When I picked her up I noticed she was very thin. I suspect the flock has kept her from food and water with their aggressive action. I will keep her isolated with her own food and water for a while. My question is what causes this sudden flock behavior and what can I do about it? Will this outcast recover and be able to rejoin the flock?