Noticed yesterday that one one my hens had a bloody featherless patch on her chest. She, along with all of the other chickens, was pecking at it. I put her inside a cage and put it in the coop to isolate her till it healed. Went out this morning to check on her and found her dead. Her head was sticking out of the cage I had her in and her neck was picked bare. There is no evidence of anything getting inside my coop to begin with. Any ideas? Will chickens kill each other?