At a cruising altitude of 30,000 feet, an airplane pilot doesn’t expect to hit roadkill. After all, Mount Everest, the world’s tallest mountain, is 29,029 feet above sea level, and the paper-thin air at its peak is hardly substantial enough for any animal to breathe for long. If you’ve ever been on a plane, you know what 30,000 feet looks like: far above the clouds, you can’t see cars on the road, but you can see the ends of the Earth. Imagine, then, the surprise of that pilot flying over Côte d’Ivoire in 1973 on a transcontinental trip, breathlessly calling in to air traffic control, Abidjan, this is TWA Flight 498 at a cruising altitude of 11,000 meters. And I think… I think we just hit a bird.
Rüppell’s Griffon Vulture is the highest-flying bird in the world, reaching a world-record 36,100 feet above sea level — 14 miles high. (The first-place reward for that particular vulture was to be sucked into a jet’s turbines. No capes!) It can achieve this dizzying height because of its unique blood, which contains a special hemoglobin agent called alpha-D which bonds with oxygen extremely efficiently. But it’s one thing to know how it survives in the upper troposphere, and another to know why any animal would remove itself so far from the Earth.
The vulture was named for Eduard Rüppell, a German naturalist on tour in Northern Africa in the 1820’s and 30’s. Rüppell, being from a wealthy and educated family, was supremely comfortable back at home, yet chose one of the most uncomfortable places for a Northern European to explore: the Sahara and the deserts of Saudi Arabia, Israel, Ethiopia, Sudan, and Egypt. Essentially, he was sauerkraut on toast. But his contributions to zoology opened up the study of a region heretofore unknown to Western science: the desert ecosytem. Rüppell was the first biologst to speculate on why the desert fox has enormous ears (in, of course, a pre-Darwinian way) and observe the scimitar oryx in situ. And watching those minute specks wheeling above him in a blindingly blue sky until they disappeared from sight, he considered the vulture.
As an avid lifelong birdwatcher, I’ve always felt that vultures get a bad rap. They terrify us with their black plumage (which they have to keep sun-warmed at those cold heights) and repulse us with their baldness (which only serves to keep their heads clean of blood). We hate them for their associations with death, and we don’t respect them because they don’t kill what they eat. To me, this makes them like most of us. I am a consummate carnivore, but I have never killed anything I’ve eaten. I rely on butchers and slaughterhouses for that, and in all likelihood, so do you. But unlike us, they keep the world clean. New World vultures — unrelated to the Rüppell’s — are in the family Cathardidae, as in catharsis. They are the purifiers.
In the Old World, such as ancient Greece, vultures picked at Prometheus’ liver, but in ancient Egypt, they were symbolic of both mothers and lovers. (Having observed vultures in the wild with some frequency, I can tell you that they are surprisingly affectionate with one another when they’re not feeding, and are very devoted to their young.) And in Tibet, the recently deceased are traditionally cut up and left on a mountain for the vultures to consume in what is called a “sky burial.” To the Tibetans, vultures are angels, consuming the now useless flesh and transporting it to Heaven. It is apotheosis, the transmutation of the base into the divine. Like a bear flung into the starry night to become a constellation, or the Viking warrior lifted to Valhalla by winged valkyries, vultures render matter into airborne energy, flesh into spirit. They transform. They elevate. They purify.
Not for the weak of stomach, though.
But back to the science. As I said, vultures are caring and social creatures, and Rüppell’s vultures are the most social, gregarious vultures of all, nesting with dozens of others in high cliffs where take-off is easier. There is a good reason for their sociability: it means more eyes on the ground. Rüppell’s vultures can cruise up to 90 miles a day in search of carcasses, and at a height of several miles, they’re still apt to miss things, even with their almost unimaginably keen eyesight. It is the scarcity of large, uneaten carcasses in the arid lands that has forced the Rüppell’s higher and higher, broadening its visual field to over fifty miles each. With each vulture in the colony spaced out by several miles, and watching both the ground and each other, they can create a dragnet surveilling hundreds of miles of savannah.
Airplanes have an optimum cruising altitude of 30,000 to 40,000 feet, below which the air is still thick enough to create massive resistance, and above which they cannot maintain enough speed to generate lift — they stall. Likewise, the optimum cruising altitude of bird with an 8-foot wingspan is between 15,000 and 20,000 feet. Rüppell’s vultures will gorge themselves on both flesh and bone — they have backwards-facing spines on their tongues for licking their plates especially clean — until they cannot even achieve lift-off, and have to peck at angry hyenas to burn off calories. But once they are able to catch a thermal, they use that fuel to find their optimal cruising altitude, a matter of weight and speed. A fattened bird, lacking a jet engine to power it through the feeble air of the upper troposphere, will fly lower. It is a thin and starving bird that can reach those exalted heights that humans have reached. Relieved of its flesh, it reaches the altitude of angels.