We've had this inherited flock for a bit over a year and a half, and this is the first predator loss. There is a small hen house (4x8') which sits in a old dog (30x80') run which has 6' tall chain link fence around it. We lock the door to the hen house each night. Up until today it has been fairly predator proof. Things were fine this AM when I opened the door and refreshed their feed. When I went to lock the house door this evening, no one was in the coop, and there were a bunch of feathers in the coop and outside too. It was about 25F and lightly snowing, so the hens should have been inside. I did some searching and found two live hens huddled in a corner of the run. I picked one up and put it back in the coop and the other followed, they were obviously shaken up and one seemed to have lost some feathers, no blood or injuries that I could see but I did not subject them to a thorough inspection. Still 3 hens missing, but the two live ones were safe in the coop with the door locked. I searched the pen and outside. I found two dead hens, in opposite corners of the pen. Both were whole, and appear to have broken necks. No blood on the ground or signs anyone had started eating them. I searched but could not find any trace of the 3rd missing hen. Also inspected the perimeter fence of the pen, and there were no signs of a hole dug underneath. Nothing that would allow a skunk or fox through, and certainly nothing big enough to fit the missing hen through.There is some snow on the ground still although it is fairly hard, but I have been seeing occasional canine paw prints around the pen, probably a fox as one has been seen around. My first question is, what critter did the killing here? There are bobcats and mountain lions in the area, certainly one of those could have climbed the chain link fence in and out, but does their killing pattern match what was found. A fox maybe, I have heard that they can climb fences. Lots of neighbor dogs, but none that could have gotten into the locked fence (unless a neighbor let it in and then back out, very unlikely). House cat? There are a few around but they don't travel much due to coyote pressure. And what would have killed 3 hens but only taken away one? Thoughts ideas? And of course, how to prevent this in the future?