Well I am only really familiar with coyotes and raccoons being threats in my area with the occasional skunk or possum but one thing I've noticed about raccoons is they don't wipe your flock out.   A friend of mine was losing on average one chicken a night for about four days until he trapped the raccoon and fortified his chicken coop.  I lost one of my birds to a raccoon attack on their forth night out in the coop and the very next night, as soon as it got dark, maybe 9:15pm or so the raccoon was back and there to get another, had already pried part of my wire back and was about to make his attack.   Luckily I was able to find him in a tree and take care of him.    But my vote is raccoon, they like to pick them off one at a time.. but there could be other predators that follow the same MO.