It's a mystery that has plagued scientists for ages: When new puddles and pools form, or a dry and isolated pond suddenly gets revived through rainfall or snowmelt, where do the fish that live in these waterbodies come from? Now, a new study might have finally found the answer: duck poop.⁠ Hungarian researchers fed live eggs of Prussian and common carp—both invasive fish species wreaking havoc in North America’s waterways—to Mallards and looked to see whether any came out the other end. They found that 0.2 percent of eggs endured the journey through the bird’s digestive tract and showed up in their fresh feces. Three of those 18 recovered eggs hatched into baby carps, the team reported on June 22 in Proceedings of the National Academy of Sciences, suggesting that Mallards, and possibly other waterfowl, ferry fish eggs between waterbodies near and far.⁠ ⁠ _____⁠ ⁠ Because Mallards are abundant and widespread, even with that low percentage, “they can move a lot of eggs because of their h...