In the lab, Vincze and her colleagues fed thousands of eggs from two invasive carp species to eight mallard ducks. About 0.2 percent of ingested eggs, 18 of 8,000, were intact after defecation, the team found. Some of those eggs contained wriggling embryos and a few eggs hatched, the team reports June 22 in the Proceedings of the National Academy of Sciences. It’s not clear yet whether eggs survive in this way in the wild.

Most of the viable eggs were pooped out within an hour of being eaten, while one took at least four hours to pass. Migratory ducks could travel dozens or possibly hundreds of kilometers before excreting those eggs, the scientists suggest.

Though the surviving egg count is low, their numbers may add up, making bird poop a possibly important vehicle for spreading fish. A single carp can release hundreds of thousands of eggs at a time, Vincze says. And there are huge numbers of mallards and other water birds throughout the world that may gorge themselves on those eggs.