I just remember I had a small batch of chicks (about a month old) in a little fence with a topper. A weasle got in there and killed all but 2 of them one afternoon. And when we were kids a spruce marten got into our chicken coop and killed 25 hens in one evening. Both times just chickens dead with their heads missing :( Sometimes there is just no warning.
Whoever said humans were the only animals who kill for sport never met a weasel, wolf or big cat.