Legend holds that the ancient Greek playwright Aeschylus, fearing a prophecy that a falling object would kill him, spent an inordinate amount of time out in open spaces. So naturally an eagle picked up a tortoise and killed the playwright by dropping it on his noggin, having mistaken the man’s bald head for a rock that could break open the prey.
The story is almost certainly not true (that would have been one hell of a shot), but eagles will indeed drop tortoises on rocks like that. There's even another kind of bird that does the same, only it doesn't bother with live prey. The beautiful bearded vulture feeds almost exclusively on skeletal fragments, swallowing bones whole when possible. What pieces it can’t swallow it takes into the air and drops onto rocks, shattering them into manageable pieces.
That’s all kinds of clever. Like any other vulture, the bearded variety---which typically flies over mountainous regions of Africa, Asia, and Europe---provides an indispensable service to the ecosystem, checking the spread of disease by consuming corpses. But the bearded’s diet is 95 percent bone. It can wait for the other scavengers to strip the body clean, then stroll in at its leisure to take its fill.
Typically it’s after small to medium ungulates---the hoofed mammals. (It’s also known as the lammergeier, literally “lamb vulture.”) “Anything that's the size of a domestic sheep,” says ecologist Sonja Krüger of South Africa’s Maloti-Drakensberg Park. “They can swallow the bones of that sized animal quite easily.”
But the bearded vulture isn’t about to pass up the bones of larger animals. Its beak and claws are too weak to break these into small bits, so instead it grabs a bone and hitches a ride on a rising column of air called a thermal. With its supreme vision the vulture targets a patch of rock and lets loose. If its aim is true, it will kill a Greek playwright---or the bone will shatter to pieces on the rock. The bird then swoops in and swallows the shards whole. If it misses, or the bone bounces on impact, the vulture will try again and again until it succeeds.
What it gets is a surprisingly nutritious meal. The bone itself of course is packed with calcium, but the real prize is the bone marrow. Fatty, energy-rich bone marrow.
For pretty much every other creature on Earth, bone is indigestible. Hyenas will chew through the odd bone here and there with their powerful jaws, but that’s by no means their main source of food. Owls, which eat things like mice whole, have to regurgitate the bones. Bearded vultures find this unacceptable: They dig bone so much they’ve been known to eat owl throwup.
You might expect that the bearded vulture’s gut would have a problem working through all of this stuff. But its solution is a metric crap-ton of powerful acid. The bird’s digestive system isn’t even elongated to handle the load, nor is there any special grinding going on. Thanks to all that acid, it only takes 24 hours for a bearded vulture to turn solid bone into poop.
And all it eats is bone, day in and day out---save for when two bearded vultures fall in love and have babies. Them feeding their sensitive young ‘uns bone would be like you feeding yours … well, bone, I guess. So “you'll find adults picking pieces of meat at certain times of the year, and even pieces of fat, off the carcass to get [the chicks] into breeding condition,” says Krüger.
But if the bearded vulture is clearly capable of eating meat, why go through all the trouble of eating bone? Two reasons. For one, nothing else, save for the occasional hyena, is going to bother with the stuff, and that’s a huge advantage when it comes to survival. And secondly, unlike other scavengers that have to consume a corpse before it spoils, the bearded vulture can and does return to skeletons time after time to cart away bones. So in effect it keeps pantries scattered across the mountains.
From all these photos of the bearded vulture you may have noticed that the bird actually has feathers on its noggin, which vultures normally don’t, and that those feathers are a beautiful red hue, or burnt sienna if you don’t have problems determining subtle colors like me.
Those feathers are there because they can be. The bearded vulture just doesn’t eat like other vultures. “The others don't have feathers on their heads so they can get into the carcasses and it won't get matted with all the liquid or blood,” says Krüger. That helps spare them the inconvenience of carrying around diseases. Because the bearded vulture swoops in later to pick up the bones, it can afford keeping a luxurious head of feathers.
As for the color, they actually apply it by rubbing themselves against cliffs and rolling around in the mud. “It's that iron oxide in the soil that gives them that color,” says Krüger. “Birds that are in captivity for a long time that aren't provided with the facility to have a mud bath, they're basically snow white.”
So what’s the point? One theory holds that it’s a signal of strength---well, at least it's a roundabout signal. Theoretically, the birds with the most deeply stained feathers spend the most time rolling in the mud. This would signal to potential mates that they’re more fit because they’re feeding well enough to have the time to fart around.
But a more likely theory, according to Krüger, is that the mud helps keep parasites at bay. An additional bonus may be that the vulture picks up minerals from the mud as it preens itself, like it's wearing a coat of multivitamins.
No amount of minerals, though, can save the bearded vulture from---yeah, you guessed it---humans. The bird faces severe threats, particularly in Africa, from hunting and poisoning.
And it’s not even the birds that the poisoning is targeting. To retaliate against predators that have killed their livestock, farmers may poison the corpses in the hope that the killers will return. Unfortunately, the scavengers are the ones who show up. On top of that, practitioners of traditional medicine prize vultures for their fantastic vision---these people think they give you the power to see the future, which more than likely isn't true.
Accordingly, the populations of vultures of all kinds are taking a nosedive. In South Africa, the bearded vulture has declined to critically endangered status. But in cooperation with the government, Krüger and her colleagues have mounted a public outreach campaign to educate farmers on the harm they’re causing. And “if we're worried there's a food shortage in certain areas, we're creating feeding sites for the birds,” she says. “Poisoning really is the biggest issue we need to deal with.”
Let’s hope it works. If the bearded vulture isn’t around to keep playwrights in check, who will?
Browse the full Absurd Creature of the Week archive here. Know of an animal you want me to write about? Are you a scientist studying a bizarre creature? Email matthew_simon@wired.com or ping me on Twitter at @mrMattSimon.
