I own and breed Red, Silver and Cross Color foxes and honestly my biggest chicken killers are my neighbor's dogs. They've gotten in my fence and killed my birds more than once. My foxes have even gotten out before (my fault, forgot to latch the pen) and I've found them in the chicken coop (after many hours of searching) without a single chicken harmed with the fox wagging their tail and squealing just tickled pink that I found them lol. I did have a coon come in a few winters ago and take chickens but he was easily captured and relocated.