Two piles of feathers and one missing altogether

Help! What would attack full grown Brahma chickens in the night/morning and leave nothing but a strewn out pile of feathers? I'm thinking Coyote or Fox. Three of my chickens disappeared yesterday afternoon as they were free-ranging. And, after searching for an hour with no sign of them, I figured they were whisked off by coyotes. But, this morning when I went looking again, I found piles of feathers around the outside of their pen and nothing else. The third is still missing altogether.

We've defied the odds in an area full of predators for an entire spring and summer. But, as the cold sets in and food is scarce, my flock has become fair game. I know that whatever it was it will return...the question is what would do this? I really don't want to lose anymore!