Thanks for the ideas gals! I didn't even think about the predator flying off with the body. That would explain why there were no bones. duh. I think I've convinced myself it was an owl and that it happened during the night while the girls were safe and snug in the coop. 
I have things strategically placed around the yard for them to duck under for this very reason. The coop and run are in one corner, I've got a pallet up on cinder blocks in another, a little hoop house chicken tractor in another, and a couple of garden trailers in the other. I think they spend most of their day under the trailers, or in the hoop house if it's raining. But, I'm definitely thinking about them a lot more than normal today...  Not only because of the grouse, but when I pulled in the driveway yesterday my little trouble-making EE had jumped the fence and was out all by herself! She is such a turd!! Her name has actually changed from Peanut, because she was the tiniest chick, to Trouble because if ever one of them is causing trouble it's her! But I can't stay mad at her and those cheeks 
		
		
	
	
  LOL