July 19, 2024

The two lappet-faced vultures had been together for just a few months, yet the massive birds, with their watchful, featherless gargoyle faces and their dark mottled body plumage so plush it looks like fur, had already mastered the avian version of monkey-see-monkey-do.

Kenya, the female vulture, hopped onto a tree stump in the middle of their outdoor enclosure at the Maryland Zoo. Shredder, the male vulture, hopped onto another stump nearby. Kenya jumped back to the ground. Shredder waited a beat and did likewise. He lumbered over to a corner of the enclosure and spread his wings wide to their nearly seven-foot span, exposing fluffy white feathers that covered his legs like a pair of bloomers. Kenya positioned herself a few inches behind him and added novelty to the mimicry, unfolding first one wing, then half of the other, then the second half: Ta-da!

It’s called mirroring behavior, Jen Kottyan, the zoo’s bird curator, said, and it was a promising sign. Lappet-faced vultures, native to Africa and named for the flaps of skin, or lappets, that dangle from either side of their head, are among the world’s most endangered birds. In 1991, the Maryland Zoo became one of the first in the United States to successfully breed the vultures in captivity, and Ms. Kottyan predicted that the newly installed pair, now 2-and-a-half years old, would prove similarly obliging.

“They’re doing really well, and they seem to get along,” she said. “So we’re hoping things will go easy when they hit sexual maturity in another three or four years.”

Brandon Jones, an animal keeper who worked closely with the vultures, threw the birds a piece of raw meat. They ripped it apart and swapped pieces of it back and forth.

“I think she’s a little smarter than he is,” Mr. Jones said.

“All vultures are smart,” Ms. Kottyan said. “I haven’t met a vulture that wasn’t.”

To the general public, vultures may seem vaguely repulsive, Edward Gorey-type characters that skulk in bare trees waiting for something to die. But to researchers who study any of the 23 species in today’s vulture consortium, the birds brim with intelligence born of their exceptional vocation.

Many animals feed on carrion opportunistically, when the occasion arises. Alone among vertebrates, vultures have taken scavenging professional. In lieu of hunting live prey, they seek out dead meat. That may seem easy — after all, everything dies. But because the time and place of an animal’s death are rarely predictable, the vulture’s reliance on carrion has forged, along with a flexible neck for poking into corpses and a featherless head for easy self-cleaning, a creative, cunning and wide-ranging mind.

“It makes sense that an animal that depends on scarce resources can really benefit from being intelligent,” said Thijs van Overveld, a vulture researcher at the Donana Biological Station in Seville, Spain.

Vultures, their fans insist, rival the famously brainy parrots and corvids in the use of tools and artful maneuvers to secure their needs and desires. Egyptian vultures, for example, have been shown to throw stones at ostrich eggs to crack through the shell, but only after an experimenter revealed to the birds that the giant eggs contained food.

Egyptian vultures have also been observed wielding twigs to rake up tufts of wool from sheep shearing pens and repurposing the wool as nest insulation.

The vultures are vain about their appearance and during breeding season will use makeup. They roll around in mud to paint their body feathers red and eat herbivore dung to extract the carotenoid pigments that will turn their white faces gold.

Black vultures in Northern California have learned to play midwife to sea lions, snipping the umbilical cords of newborn pups and then feeding on the placenta.

To explore problem-solving in turkey vultures, researchers applied the classic string-pulling test. They dangled chunks of quail and chicken meat from 24-inch nylon strings attached to a wooden platform and then challenged a half-dozen vultures to step onto the beam and try to retrieve the hanging prizes. In previous trials with ravens and parrots, successful birds relied on foot power, pulling up a bit of string with their bill, tucking it under a talon, and then pulling up more. But the flat, webbed feet of the turkey vultures proved ill-equipped for grasping, so three of the cannier vultures took a different tack: They sucked up the nylon thread like a strand of spaghetti and then appeared to stash it in the throat crop that serves as their all-purpose food storage device, until at last they could seize the meat and expel the string.

“Vultures are masters of innovation when it comes to scrounging for food,” Dr. van Overveld said. In a 2021 paper in Animal Cognition, he described vultures as “as an overlooked model in cognitive ecology.

Also impressive is what might be called the vulture’s wide-angle intelligence, the way it scouts for scarce and fleeting resources across vast panoramas of land and sky Researchers who track the bird’s movements with satellite transmitters have been astonished to see just how far vultures fly, sometimes nearly 20,000 miles per year. “They educate you about the landscape,” said Corinne Kendall, a vulture expert and conservationist at the North Carolina Zoo in Asheboro, N.C. “By making these big movements all the time, they show you where connectivity might exist between one place and another.”

Airborne vultures seek not only carrion but also the next source of uplift. Many vultures are big birds. The king vulture of Central and South America, for example — its head and neck so brilliantly festooned with patches of red, blue, yellow, purple and orange that some consider it the reigning beauty of vultures — can weigh 10 pounds or more, whereas an average American crow is 21 ounces.

Vultures need the bulk to help weather carrion scarcity, but their heaviness makes active flying, with wings flapping, especially costly. Vultures have addressed the contradictory demands by becoming some of the world’s finest gliders. They stay aloft for hours on breezes and thermals — columns of hot rising air — and as one thermal degrades, vultures move on to the next.

Emily Shepard of Swansea University in Britain and her colleagues studied flight performance in Andean condors, which at an average of 24 pounds are among the most massive soaring birds in the world. The scientists learned that the costs of gliding for condors were extremely low, barely twice the caloric expense of resting on the ground. Flapping, by contrast, burned about 30 times more energy than doing nothing. “For a bird as big as a condor, flapping is really like a sprint,” Dr. Shepard said, and condors in flight do it just 1 percent of the time, a far lower flapping rate than is seen in other long-distance gliders like albatrosses and shearwaters.

Vultures may find fresh thermal columns by watching cloud patterns, revisiting reliable updraft hot spots and, above all, by spying on other birds, tuning in to a kind of aerial Waze. “Just as any glider pilot will tell you: If you see birds circling, that’s where you fly next,” Dr. Shepard said.

To scan widely, vultures rise high, climbing 10,000 feet or more into the air. With eyesight as sharp as that of an eagle or falcon, vultures can detect tiny variations in the landscape that might signal current or soon-to-be carrion, like displacements in the grass as a predator disembowels its prey. Some vultures add a keen sense of smell to their surveillance. A high-flying turkey vulture can detect a single odor molecule wafting up from old meat. “Turkey vultures probably have the best sense of smell of any animal that’s ever existed,” Dr. Kendall said.

When vultures spot a potential meal, they drop earthward at dizzying speed, plunging thousands of feet in a matter of seconds. “They sound like little rocket ships when they land,” Dr. Kendall said. They attack a carcass vigorously, different species stepping in as their skill set and brazenness permit. If a wildebeest dies in Tanzania, for example, large-billed behemoths like lappet-faced vultures or white-headed vultures will make the first pass, tearing into the tough hide and exposing the cavity, followed by midsize white-backed vultures that crowd in for their share of flesh, fat and viscera. Finally, smaller hooded vultures will go for the bones. After an hour or two, the remains of the 450-pound herbivore won’t be enough to stock soup. Predators eat just 30 percent of available meat; vultures take care of the rest.

“It’s such an industrious and well-layered system of clearing away carcasses,” said Aaron Nicholas, a vulture conservationist with the Wildlife Conservation Society. “There’s nothing to compare with it.”

The sanitation benefits run deep. Vultures reduce the greenhouse gases that decomposing corpses emit, and remove from the environment a host of potentially pestilent microorganisms found in rotting meat. The bacteria behind anthrax, tetanus or botulism? A vulture’s idea of spices.

New research suggests that vultures have evolved an array of defenses to counter pathogens and bacterial toxins that would sicken or kill other animals. Not only are their stomachs famously acidic, but the vulture microbiome, the set of microbial communities that populate the bird’s gastrointestinal tract, throat, face and other body parts, clearly plays a protective role, too. In preliminary assays of vulture fluids and tissue samples, researchers have identified beneficial microbes that block Yersinia pestis, the bearer of plague, and listeria, the cause of food poisoning. They have found an army of phages — viruses that can attack pathogenic bacteria — and genetic instructions for the production of antibiotics, antiparasitic compounds and insecticides. And they have detected tiny invertebrates called rotifers that feed on bacteria and protozoa. There is good reason, Mr. Nicholas said, “that vultures are often referred to as the soap of the savanna.”

That microbiomic soap likewise keeps a vulture’s mouth clean. Lauren Pharr Parks, a vulture expert and forensic consultant, recalled the time she was radio-tagging turkey vultures as a graduate student in Louisiana. One bird bit down hard on her finger, puncturing the skin. “It hurt so bad, I thought I’d lose the finger,” she said. “I thought I’d get rabies.” For hours she was too busy to stop and clean the wound, and when she finally got around to it, she was amazed to find that the injury had disappeared. “I’ve had paper cuts that last for days,” she said. “But in this case there was no redness, no swelling or tenderness, no pus, no infection.” she said. Vulture saliva, she suggested, could hold medicine’s next blockbuster drug.

For all their importance to the smooth running of nature’s threshing machine, vultures themselves are being mowed under at an alarming rate. Sixteen of the 23 vulture species are listed by the International Union for the Conservation of Nature as threatened or endangered, four of them critically.

Among the biggest menaces to vultures today, experts said, is poisoning, both incidental and intentional. Wherever there is conflict between people and carnivores, vultures often end up as collateral damage. The standard scenario is this: Farmers who lose livestock to predators like lions or hyenas will fight back by setting out a carcass laced with pesticides. But while the lion may return and take the bait, Dr. Kendall said, “30, 40, 50 vultures will come in and also die.”

Or many more: In the last few years, single poisoned carcasses have led to the deaths of over 1,000 hooded vultures in Guinea-Bissau, and close to 800 in Botswana. In Mendoza, Argentina, in 2018, 34 Andean condors died after feeding on a poisoned carcass. “This could be 10 percent of the condor population in that area,” said Sergio Lambertucci, who studies condors at Argentine Research Council and the National University of Comahue.

Poachers will also kill vultures deliberately, to prevent the birds from blowing their cover while they are extracting valuable tusks or horns from the mammals they have slain.

By far the most devastating case of accidental vulture slaughter took place in India in the 1990s, when tens of millions of vultures died after feeding on the carcasses of cattle that had been treated with diclofenac, an anti-inflammatory drug. By the time experts figured out what was happening, the Indian vulture population had collapsed by more than 99 percent. Hard-hit species like the white-rumped, long-billed and slender-billed vultures may never recover.

Scientists and conservationists are working fiercely to stem vulture declines, through community outreach and education; negotiating with government officials, farmers, ranchers, anybody who lives in the vicinity of vultures and has clout; basic research and captive breeding programs to keep vulture stocks going. Captive-bred animals are rarely released into their natural environment, but Ms. Kottyan, of the Maryland Zoo, has some hope for the descendants of Shredder and Kenya.

“If we can tackle all the problems that lappet-faced vultures now face in the wild,” she said, “maybe we can get some of our birds back out there, too.”

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