What leaves heads behind?

We have had a predator lately killing our smaller chickens, ones which were too big for brooder and recently introduced to flock. This was ultimately our fault, as we put them on the roost at night but did not check to make sure they stayed in the chicken houe. We have since placed our dogs on chains outside of the chicken pens and closed the chickens up at night. But anyway..several mornings in a row we found only the heads of a few of the chickens left in the chicken yard and we were trying to figure out what animal leaves the heads. The main types of predators we have around here in this part of Louisiana are bears, foxes, owls, coyotes, and bob cats. There have been no feathers left behind, just heads. One larger chicken was outside of the pen one morning with only its head removed, and one of the small chickens whose head was left behind, we actually found its wing in a different chicken pen than its head. It was really weird. Any ideas? Dogs are keeping whatever it is away, but we are curious.