Twice in the last month I have went into my chicken coop to find a dead chicken with it's head gone. I have a secure coop and there is no sign of a predator. Not really any blood or scattered feathers, just missing it's head. Could the other chickens be doing this? It is a one year old hen. I don't have any neighbors that could be messing with me or anything like that. There isn't any other sign of trauma and I'm very confused. Does anybody have any ideas?