... humans ARE predatory mammals, though. I have been a vegan for eleven years and I have no qualms admitting that biologically, I am an omnivore and predator. We are not true carnivores, but that does not change the fact that we prey on other species just like a black bear or other predatory omnivore does. Our natural history confirms as much, and while we developed argiculture to have a constant availability of prey, that doesn't change biology. On a very literal level, the #1 predator of chickens is humans, because we kill and eat more of them than any other species does.
I also see a lot of talk about predators killing "for the fun of it," but realistically what we are seeing is an instinctive behavioral response gone haywire by being thrown into an unnatural context. In nature, opportunities like a massive group of confined and fairly helpless prey concentrated in one spot just doesn't happen. Predatory responses are elicited by certain behaviors and conditions, and a large ammount of easy prey flapping around squawking and panicking is really too much stimulus and typically results in a massive overkill. It's not much different than working your cat into a frenzy with the rapid movements of a laser pointer - they just can't help themselves! But very little of this could be attributed to a sense of "fun" as there is little to nothing in literature indicating that wild predators are flooded with pleasure chemicals when they kill - and really, those would be counterintuitive since most pleasure biochemicals tend to have effects like lowering heart rate, reducing aggression, producing calm behaviors, etc.
All that being said, I do agree that humans do not really fit this poll's intended purpose though, as I can assume it was asking what species people had their most losses attributed to. When I worked at an animal sanctuary, the big culprits were rats and mink; they seem very adept at getting into virtually any enclosure, and all it took was a weak hen staying on the ground... gone. I've never lost any of my chickens but my neighbors constantly lost hers to hawks as she did not contain them properly. I decided to vote "rat" on the poll because I feel they are the hardest to keep out. You can keep foxes, raccoons, coyote, etc. out with appropriate fences, you can deter hawks with a roof on your coop or run, but those darned rats seem to find ways to get into even the most secure coops.