To me, it doesn't look like the critter in the first pic has a tail. If so, it rules out any kind of cat or canine. My first thought was a small bear. The light patch of fur on its butt is common to bears, as they often sit on their butts like we do. I've seen a lot of pigs, and it just doesn't look like a pig. Bottom line.....regardless of what it is, you've got predator problems. All you can do it fortify your coop, and hope any of your birds who aren't inside at night can get up high. I'd consider an electric fence if things get bad enough. We've been lucky - we have lots of wolves, coyotes, skunks, and the odd bear, but we've never had any problems, aside from one skunk taking a few scratches at the ground around the girls' run at night, but he lost interest quickly.