Cold-blooded baby bird killers.
Cold-blooded baby bird killers. Max Pixel/Public Domain

Mallard ducks don’t seem like particularly vicious animals. Their chicks are adorably awkward and fluffy, and they stick their butts in the air while they’re looking for food. But not all ducks are content to look for plants on the bottom of a pond. Some ducks, such as some mallards in Romania, for example, have developed a taste for other birds.

The ducks were spotted by researchers from the University of Cambridge and Romania’s Veterinary and Food Safety Authority at a reservoir last summer. They noticed one adult and ten juvenile mallards along the shore, “vigorously shaking” the vegetation. But then the adult started shaking its head and squishing whatever was in its beak. It turned out to be a fledgling Grey Wagtail. After a struggle with the fledgling’s wings, the adult managed to gulp down the poor wagtail whole.

But the mallards weren’t done. They went back to the vegetation and flushed out another bird, this time a Black Redstart fledgling, and the juvenile mallards either drowned the fledgling or ate it. Then, the researchers write, they “emerged onto a floating tree trunk for basking and preening as the group entered a phase of rest.”

Ducks are known omnivores that sometimes eat fish or crabs when they can’t get enough protein in their diet otherwise. But this is the first time they’ve been documented as cold-blooded killers. “The fact that these individuals seem to have learnt how to hunt birds is pretty extraordinary,” Silviu Petrovan, a coauthor of the report, told the BBC. “Potentially there is quite a lot of pressure for those fast-growing juveniles to get animal protein intake, and therefore they are looking at opportunities to supplement that.” Ducks haven’t evolved to eat other birds, which is why it was so hard for the adult to get that wagtail down. Also, said Petrovan, “digesting bones and feathers – that’s not something that mallards have really evolved to do.”