This morning I found my 6-month-old female mallard beheaded and with an empty chest cavity in a well-fenced goat pen where she liked to hang out. No other damage except to her upper torso that I could see. We have snakes in the area: racers, rat snakes, and I saw my first rattlesnake in nearly 5 years near the pen a couple of weeks ago. I can't think of another predator that would do that kind of damage. I'm leaning toward the rattler as I had a racer and a ratsnake living in the chicken coop this past summer with nothing more than the loss of a few eggs (at least until the hens started laying outside and we started losing a lot more eggs!). I have mainly standard-size chickens, which are bigger than the sweet little mallard was, but I also have 4 bantams that are smaller. The other frequent predators in the area are hawks and owls and coyotes, though I'm pretty certain it wasn't any of them because there weren't feathers or other marks save for a ripped-up shoulder. I know snakes will generally swallow prey head first, so that fits, but would they be able to decapitate a duck if they couldn't swallow it whole? I have the little mallard's mate to watch out for as well as four Pekin ducks and a rooster in my backyard, and a flock of 27 chickens that free-range nearby.