Over the last 3-4 weeks i have lost four of my chickens, my BLRW roo, my lakenvelder pullet, my polish cockerel, and my black langshan pullet. There is snow on the ground, so EVERYTHING leaves tracks. The only tracks i have seen are rabbit tracks, and ground hog tracks. I have checked in the coop for predators, and cant find any openings for predators to get inside. What is it?