In 2015, Harold Greeney trained his camera on a mourning dove nest stitched into the crook of a cactus. As an ornithologist, Greeney studies the love lives of birds—cooperative breeding in nightingale-thrushes, parenting strategies of spotted barbtails, breeding biology in speckled hummingbirds, you name it. His goal today was to capture the breeding habits of doves in an urban setting. Instead, he captured perhaps the most horrifying bird-on-bird behavior the world has ever seen.

The video opens on what appears to be a lovely day in Tucson, Arizona. Birds chatter in the background, and a pair of mourning dove chicks warm themselves in the day’s new rays. For six glorious seconds, the scene is full of beauty and promise. Then another bird lights upon the edge of the nest. This bird is no Mother Dove returning with a breakfast of seeds and crop milk: It’s a Gila woodpecker, with wings of barred black and white and a long, sharp beak. And it's come in search of a meal of its own.

What happens next may upset you (and in fact, if you’re sensitive to bird-on-bird violence, you may want to stop reading here). Before the chicks even realize there’s an enemy at the gates, the woodpecker cocks its head back and starts to peck … their skulls. The Gila’s head moves like a pneumatic hammer, up and down, up and down, drilling into flesh and bone with the force of 1,000 G’s. Soon both chicks’ skulls have been opened up like coconuts. At this point, the woodpecker begins extracting brain and blood with its long, sticky tongue.

The whole assault lasts less than three minutes. Then one of the adult doves returns to find the avian equivalent of Hannibal Lecter carving up its young, one of which has already tumbled from the nest in a braindead daze. At no point does the woodpecker appear to deal the chicks a death blow. Yet while each continues to thrash and cower throughout the affair—which almost makes it worse for the viewer, and doubtlessly the chicks—their doom is abundantly clear.

It’s a profoundly disturbing, vicious scene. But from a scientist’s perspective, it’s also an amazing find. As far as Greeney can tell, no one has ever filmed this behavior before.

Greeney has a possible explanation as to what’s happening—but it probably won't make you feel any better. When Gila woodpeckers get thirsty, he speculates, they crack open a couple of nestling heads like you or I might open a six-pack. “My guess is that these woodpeckers, like most birds in the Sonoran Desert, are fluid or water stressed,” he says. “This woodpecker appears to me to be clearly targeting the heads of the nestlings, and thus purposefully opening them to drink fluid—and this may be something that happens more often than is documented.”

Yep, you heard that right.

Most of us assume that woodpeckers use their prodigious powers primarily to open up tree bark and deal death blows to insects. But to see how unusual this behavior truly is—and how surprising it would be to other ornithologists—I reached out to one of the most experienced birders you’ll find anywhere: Geoff LeBaron, an ornithologist and director of the National Audubon Society’s Christmas Bird Count. “I’ve never seen anything like this,” LeBaron told me over the phone while he watched video of the woodpecker’s attack in real time. “It’s kind of gross, actually.”

Without any personal experience, LeBaron checked the Gila’s species profile on the Birds of North America Online—an extensive Rolodex of all the known birds in North America—for clues. He found that Gila woodpeckers have been known to have a taste for flesh: They’ve been observed accepting suet meat (the fat found around cows’ or sheep’s kidneys) at feeding stations, and have also been seen chowing down on beef bones and bacon rinds. Furthermore, the birds have been recorded preying on earthworms, small lizards, nestlings and eggs.

But there was no mention in the literature of predatory lobotomies.

Those who have studied these birds specifically tell a different tale, however. Jerome Jackson, a lifelong woodpecker expert known for his work on the ivory-billed woodpecker, says he’s witnessed this gruesome behavior occasionally in red-bellied and red-headed woodpeckers, both species closely related to the Gila. “They do generally go for the skull and the brains,” says Jackson. “A young bird's skull is very soft, sometimes parts of it not becoming hard bone until well after the bird leaves the nest. This feeding behavior is essentially the same that the woodpecker would use to feed on a large fruit with a tough rind, only the pulp inside is brain tissue.”

The thing is, woodpeckers aren’t picky. They’ll eat any part of a carcass they can access—including breast meat, lungs, heart and fat deposits, says Jackson. So eating brains may be a seasonal feeding strategy, since nestlings are only really around for a few weeks of the year before they fledge, says Clifford Shackelford, an ornithologist with Texas Parks and Wildlife. In this way, dove brains are like the fresh, local peaches you find at the farmer's market at the height of ripeness. Yum.

But how could such a brutal behavior have evolved? Remember that natural selection results in specialized appendages that are adapted for their immediate environment. The woodpecker’s anatomy, of course, is built for drilling neat little holes into things and then drawing out what’s inside with their long, tentacle-like tongues. So it makes perfect sense that they could easily learn to exploit another food source using essentially the same strategy.

If you think about it, a nestling skull isn’t all that different from an egg, points out James Kellam, a downy woodpecker expert at Saint Vincent College in Pennsylvania. (Though Kellam does admit that this doesn’t make the behavior any easier to watch. In his words: “Oh my goodness, it is gruesome. You didn’t warn me that it’s R-rated!”)

But perhaps no part of a woodpecker’s specialized anatomy is more impressive than its tongue. Not only is it long, sticky and perfect for slurping up insects. It's even more well-adapted than that: Like the beaks of the Galapagos finches, different woodpecker species have different types of tongue tips. For those that eat ants, like the northern flicker, it’s long and flat, but in grub-eaters, like the pileated woodpecker, it’s barbed—all the better for raking those juicy larvae out of their hidey holes. For woodpeckers that prefer to milk trees of their tasty liquids, like the yellow-bellied sapsucker, a brush-shaped tongue tip acts like a mop.

Moreover, the woodpecker’s tongue has another feature that would make this bird a great football player. That tongue is a crucial component of its anti-concussion apparatus: As you can see in this video, the tongue actually forks once it enters the bird’s mouth, then wraps all the way up and around the back side of the skull before meeting again on the bird’s forehead.

In some species, like the gray-faced woodpecker, all this hidden bonus tongue can actually stretch longer than the bird itself—you know, if you were to cut it out and lay them side by side. In addition to the hyoid bone, the tongue helps secure the woodpecker’s skull as it strikes its target—be it birch tree or baby bird.

My point: Woodpeckers are beautiful, brilliantly-adapted birds that have found a way to thrive across a diverse range of habitats by eating whatever they can get their clever little tongues around. You can call them needle-nosed zombies because they eat brains and babies, or you can call them survivors. Either way, if Hitchcock’s The Birds ever comes to pass, you may want to invest in a motorcycle helmet.