What Not To Serve Buzzards For Lunch, A Glorious Science Experiment

By Robert Krulwich

Published June 26, 2014 at 1:48 PM EDT

OK, I'm doing great science experiments. We've done sex (see previous post). On to lunch!

This is the story of a bird, a puzzle, and a painting. The painting, curiously, helped solve the puzzle, which is: How do vultures find food?

In America, back in the 1820s, everybody knew the answer. Vultures are scavengers. They eat dead things. Dead things smell. Vultures flying lazily in the air presumably pick up a scent and follow their sensitive noses to lunch. That was just common sense.

But John James Audubon (soon to be renowned illustrator of birds) had a different view. He often walked in the woods, and when he'd encounter a buzzard, even if the bird should have smelled him coming, it didn't. He said he'd get very close, and only when in plain sight did the buzzard startle and fly off.

Why was that? Audubon suspected that buzzards don't smell very well. Maybe, even, they don't smell at all. So he designed a test.

He got some deer skin and wrapped it around some dry grass, creating a deer pillow. Then he sewed the whole thing together, fashioned a deer head, painted two eyes on round mounds of dried clay, and then dragged the "body" to the middle of a meadow and waited.

According to Benjamin Joel Wilkinson, in his 2013 book Carrion Dreams 2.0, a vulture very quickly appeared, dropping down from the sky. It approached the hump of straw, took a nip or two, then began to rip at the pillow, tearing the stitches apart until, as Audubon wrote, "much fodder and hay was pulled out." But, of course, no meat. The bird seemed puzzled.

This thing on the ground looked like lunch, but after searching through the hay, the vulture flew off. And then, as Audubon watched, it swooped down to grab a skinny garter snake (do live snakes give off odors?), and went off with its catch. That bird could clearly see. Its eyes were excellent. But its nose? Now Audubon was very interested.

So he tried a second experiment.

On a hot July day, he took a dead hog, dragged it into a meadow and covered it with cane stalks. It was smelly — very smelly — but invisible. Buzzards flying about in the sky never — not once — came down to eat. Dogs showed up, but no vultures.

From this, Audubon formed a tentative conclusion: that "the power of smelling in these birds has been grossly exaggerated, and that, if they can smell objects at any distance, they can see the same objects much farther."

On Dec. 16, 1826, Wilkinson tells us, Audubon gave a formal talk to a group in London. The audience, it turns out, was very interested. Vultures in those days were important garbage collectors on farms, and both America and Britain had lots of farmers with strong opinions about these birds. Some found Audubon's proposition daring, fascinating. Some thought him dead wrong — so wrong, wrote British writer Charles Waterton, he "ought to be whipped." Tempers flared. Waterton's supporters began calling themselves "Nosarians" and wrote to the newspapers about the times they'd seen vultures smell their way to meals. Audubon's experiments, they said, were clearly flawed. Audubon's supporters, now Anti-Nosarians, argued that Audubon's field work had raised serious doubts about the vulture's sense of smell. More experiments, they said, were needed.

So more were done. In Charleston, S.C., the town's most admired ornithologist, the Rev. John Bachman, appointed a group of local professors, doctors and members of Charleston's prestigious philosophical society to investigate the question: Does the vulture use its nose?

Charleston was rich with turkey buzzards and black vultures. In the winter of 1833-'34, some local boys killed a vulture and the adults took it, covered it with rice chaff, and placed it in a conspicuous place. It smelled. But it was invisible, and, as Audubon would have predicted, no birds came to eat.

Next they took a hunk of rotting meat and put it under a platform (where the air could pass through). The smell, they later reported, went "far and wide"; there were many birds in the vicinity, and yet, after 25 days, not a single vulture had visited. The dogs found the meat, but not the birds.

Then came the moment that I love. I don't know what inspired him to do this, but Bachman (not Audubon — it would be an even better story if Audubon had done it) arranged for a local artist to make a painting of the Perfect Vulture Meal.

It depicted a plump sheep, skinned and cut open, with hints of delicious entrails hiding within. Lunch-porn, if you like. The group then took the painting to a yard or meadow, and placed it on the ground, facing the sky. Right away the vultures noticed.

A group of birds swooped down, landed, and "commenced tugging at the painting." They could see the entrails, but for some reason, what they saw was and wasn't there. They pecked. They yanked, and "seemed much disappointed and surprised," Bachman reported. The whole thing, he confessed, "proved very amusing."

It really must have been, because they repeated the experiment more than 50 times; and they might have kept going, but the meat was getting stinkier, and, according to Bachman, he and his team "feared, if prolonged, they might become offensive to the neighbors."

But before they were done, just to see, Bachman placed the canvas "within 15 feet of the place where the offal was deposited." I'm imagining a pile of rotting meat covered by a skimpy cloth, all of it sitting within spitting distance of an oil painting, and all the birds are focused on the art.

Or, rather, on an artful version of food. Real food didn't make an impression. Not one bird, Bachman wrote, "evinced the slightest symptoms of their having scented the offal, which was so near."

The scholars in Charleston had seen enough. In March 1834, they sent London's Magazine of Natural History their paper, which found that vultures are "guided to their food altogether through their sense of sight, and not that of smell." So Audubon won. After these experiments people in America and Britain changed their minds about vultures, except for this ...

It turns out — because nature doesn't have to be all one thing or another — that some vultures do, indeed, have a sense of smell. Most of the birds Audubon and the Charleston team saw were probably black vultures, who hunt with their eyes, not their noses. Turkey buzzards, on the other hand, can smell and use that sense all the time. That discovery was made, oddly enough, by engineers who worked for the Union Oil Company in Texas. In the 1930s, they suggested putting fragrant organic chemicals in an oil pipe, so that if the pipe leaked, buzzards might gather above the leak, signaling, "Problem Here!" The oil company tried it, and it worked. Turkey buzzards, they learned, smell perfumed oil.

Good experiments, it turns out, aren't always done by professionals. Amateurs of all sorts — painters, doctors, ministers, bird-killing boys, oil engineers and bird watchers — can pitch in and discover secrets too. When it comes to nature's mysteries — even vulture mysteries — everybody wants to know.