The bodies started arriving in 2005—dead birds, dozens of them, ferried in coolers. Cedar waxwings, grey-brown birds about the size of a person’s hand with vivid red dots on the tips of their wings and a yellow, raked-back crest, were dying by the flock in suburbs across Los Angeles. They seemed to be committing suicide, throwing themselves at windows and walls like something out of Hitchcock. Animal Control would show up, and the dead bird would end up in San Bernardino, about half an hour east of downtown LA by freeway, in the lab of a diligent veterinarian named Hailu Kinde.

Kinde, a sort of animal coroner, worked for UC Davis and the state of California. His job was to figure out what killed animals—not just birds, but livestock, horses, whatever. The point was to figure out if there was an ongoing threat, a disease that might jeopardize the local economy or people’s lives. Over the next couple of years, Kinde took delivery of almost 100 waxwings.

A bird necropsy starts at the throat. Kinde uses scissors to cut downward, to the top of the chest, and then he cuts off the legs—he prefers the word “disarticulate.” The next step is to peel the skin and feathers upward, exposing the muscles of the breast. “Once you have the breast muscle, on each side you go with the scissors,” Kinde says. “And then you have the thoracic and abdominal organs open to you.”

The first thing Kinde noticed in the birds was damage, bits of bleeding and bruising to the muscles. No surprise—they’d run into buildings. In most of the birds, the liver had also burst, another hallmark of collision. But it was the throat that took Kinde by surprise. Cut open, the esophagus of each was packed with tiny red berries. “And then we go down to the stomach, the gizzard, and it’s engorged, too,” Kinde says. That’s not weird by itself; cedar waxwings are frugivores. They live mostly on fruit. But it started Kinde thinking. “The immediate cause of death in these birds was trauma,” he says. “But why?”

Kinde sent samples of the birds’ tissue for the usual tests—heavy metals like mercury and arsenic, organophosphate pesticides, West Nile virus, avian influenza, bacterial infection. And he hit the books. Cedar waxwings sometimes get disoriented because of heat, but only at a certain time of year, so that wasn’t the answer. The fruit, though, was interesting. They were from an invasive ornamental pepper tree that grows clusters of bright red berries, inducing animals like cedar waxwings to eat them and spread the seeds via droppings. When the fruit ripens and animals don’t get to it right away, yeast moves in. Pepper fruit can ferment right on the tree.

So next Kinde sent the intestinal contents of one of his birds out for an ethanol screen. He got a major hit—226 parts per million. “It was much, much higher than the amount of alcohol that would make a person intoxicated” Kinde says. Cedar waxwings get anywhere from 85 to 100 percent of their calories from fruit, and the pepper berries seemed to be the only thing available to them. Kinde concluded that the birds were stuffing themselves on fermented berries and trying to fly while intoxicated. Disoriented, they’d fly right into a building.

In other words, the pretty birds got smashed, and then they got smashed.

You’d think that a fruit-eating bird would be ready for that eventuality, right? Like most toxins, ethanol gets processed in the liver, and in fact cedar waxwing livers are, as a matter of ratio, larger than in other birds. Some ornithologists initially disputed Kinde’s claim—they couldn’t imagine the birds eating enough fermented fruit to overwhelm their ability to handle it. So Kinde sent them his pictures of sliced-open birds stuffed with whole berries from beak to gizzard like something sent down from the kitchens of ancient Rome. The ornithologists shut up.

The literature records other instances of cedar waxwings getting drunk and failing at flying. In fact, pretty much every animal in the wild occasionally partakes. In 2010 Indian elephants got into homemade rice wine intended for a village celebration and went on what newspapers described as a “drunken rampage,” killing three people. Egyptian fruit bats sometimes have trouble flying after eating fermented fruit. Now, it’s more controversial to say that non-human animals seek out fermented fruit for its psychoactive effects. As far as I can tell, most of the recorded instances of animal boozing are accidental, or take place when non-humans would starve if they didn’t eat the fermented stuff—as was the case with the cedar waxwings.

But what about human animals? What about primates? It’s hard to tell without falling into an evolutionary just-so story, but Steven Benner—a researcher who does a lot of work on the origins of biological processes like fermentation—has a hypothesis. At a recent scientific meeting, he talked about some work he was doing on the ancient antecedent of the enzyme we humans use to digest ethanol. He said that by inferring its structure back along evolutionary time (looking at commonalities among primate species today and working backward) he’d found a point about 10 million years ago where that enzyme got 50 times as efficient. That would’ve been about when some common ancestor of humans, chimps, and gorillas got more terrestrial, climbing down from trees. Maybe the fruits that had fallen to the ground were more likely to be fermented than the ones our great-to-the-nth-power grandparents picked fresh.

And maybe at that point they started to enjoy it.

Homepage image: Randen Pederson/Flickr