From what I gained from the beginning post is that if the loses occurred in daylight it is likely a hawk, if the loses occurred after dark a varmint like a possum is likely responsible. The catch is that we don't know the age and size of the killed birds, but by them hiding in the coop and one hen taking a powder by hiding out somewhere else I will say that you are dealing with a hawk. There is also the possibility that a hawk lets' say made the first kill and some other varmint scavenged the body.