Since introducing a flock of 20 free-ranging ducks, I've seen a sharp drop in voles and mice in my fields. Ducks are omnivores and eat whatever they can catch and swallow: slugs, bugs, worms, weeds, and seeds. I've also watched them hunt out mouse and vole nests and eat the young, which knocks the population down fast. It's not something people talk about much, but I've seen it firsthand.
