I used to have a fox problem with my flock. The worst time was when a fox dug under my chicken wire and somehow got into my coop and killed my 17/21 chicks. I walked out in the morning and saw few feathers and 4 headless, dead chicks in the run. The rest were no where to be seen. I'm guessing it probably was a coyote because I've heard coyotes don't leave anything behind...