The Thing with Feathers (3 page)

The homing ability of birds can be positively eerie, which has led generations of researchers and psychologists to wonder whether an ambiguous sixth sense might be involved. In 1898, one Captain Renaud, a French specialist in charge of the military pigeon service, called this the sense of orientation—distinct from sight, hearing, smell, touch, and taste—and attributed it to some organ in the canals of the inner ear. More recently, the controversial biologist Rupert Sheldrake, known for his compelling investigations of telepathy, crystals, and Chinese medicine, has suggested “the existence of a sense of direction as yet unrecognized by institutional science” in birds and other animals. Sheldrake operates on the fringes of science
and belief—the journal
Nature
called his first publication “a book for burning”—but the bestselling author attributes his distrust of hard-nosed science to years of keeping homing pigeons as a boy. When he bicycled far from his house to release his pigeons, they’d always beat him home, and scientists couldn’t explain how. Years later, Sheldrake continues to ask questions inspired by those birds, and scientists are still working on the answers.

It’s easy to see why Renaud, Sheldrake, and others became so mystified by the navigational ability of birds; their sense of direction sometimes seems like magic. But we actually know a lot about how birds navigate. Over the past few decades, researchers have demonstrated that birds can orient themselves based on visual landmarks, the sun, and stars, and even by sense of smell, just like we can. Increasingly sophisticated research now shows that birds are also able to find their way using methods unimaginable to humans, such as magnetic fields, polarized light, echolocation, and infrasound. You can blindfold a bird, cover its nostrils, cover its ears, transport it far from home in a magnetized cage, and, more often than not, it will still manage to find its way home. With so many techniques at their disposal, the question becomes not how birds find their way, but how they ever manage to become lost (a rare occurrence). Yes, we can learn a lot from pesky pigeons.

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PIGEONS WERE FIRST DOMESTICATED
at least 5,000 years ago, even before chickens, probably near Mesopotamia. Egyptians were apparently training carrier pigeons by 1000 B.C., and some of the world’s most influential leaders, including Genghis Khan and Julius Caesar, used them for long-distance communication.

For a while, homing pigeons were most notable for their use in military operations. When Napoleon was defeated at Waterloo in 1815, a swift-flying carrier pigeon delivered the message from present-day Belgium across the English Channel to Count Rothschild, of the Rothschild banking dynasty, who was apparently the first person in England to hear the news. The quick-thinking count made several critical financial decisions and amassed a considerable fortune based on his advance knowledge of the outcome of Napoleon’s last campaign.

During the four-month siege of Paris in the Franco-Prussian War, in 1871, the French military used hot-air balloons to transport carrier pigeons over enemy lines, fitting the birds with microfilm that could accommodate hundreds of notes at once. The birds carried more than a million messages into Paris from points as distant as London.

Historians have estimated that half a million pigeons were used by the combined armies of World War I. The U.S. Army Signal Corps used thousands of birds, including one named Cher Ami that saved two hundred U.S. soldiers in 1918 by delivering a message despite a direct shot to the breast that took out one eye and shattered a leg. The heroic bird was later awarded the French Croix de Guerre (War Cross) for her service; she died after retiring to the United States in 1919, and was mounted for display at the Smithsonian Institution. During World War II, the British military alone employed some 250,000 carrier pigeons. Though radio was already widespread, pigeons were ideal for situations requiring radio silence, and they were embraced by both sides of the conflict. Military pigeon programs were eventually disbanded in the 1950s.

The civilian sport of pigeon racing, meanwhile, took off in Belgium in the early nineteenth century when fanciers began to focus on speed and endurance. From there, the pursuit spread
to the rest of the world. With the invention of a “rubber countermark” device to measure finishing times in the 1880s, breeders were eager to pit their birds against one another in local races. Military pigeons may have been phased out, but pigeon racing remains as popular as ever. Not much has changed since the early days, except that the stakes are now higher in international events.

Taiwan boasts the most racing events of any single country, with more than half a million Taiwanese enthusiasts participating. Belgium remains a pigeon powerhouse, and racing is popular across most of Europe. The United States has its own racing union, as do most developed countries, with tens of thousands of registered lofts across North America. It’s likely that right now, as you read this, pigeons are competing in an event somewhere in the world.

In a typical pigeon race, owners bring their birds to a common starting area, then the pigeons fly to their respective homes—so each bird covers a different distance, depending on its destination. Winners have the highest average speed. Recently, “one-loft” races have gained momentum: young pigeons are shipped to a single location, where they are trained months ahead of time to return to the same loft with all the other entrants so that on race day the group starts and ends together, more like a traditional marathon. Because all birds receive the same training, these races measure the quality of the birds themselves.

Some pigeons have more natural ability than others. Feral city pigeons seem to have a poor sense of direction, as do the doves in pet shops. (The white “doves” sometimes released at weddings and funerals are usually specialized homing pigeons. Untrained birds are apt to get confused, flutter in circles, and fall victim to cats and hawks, not something anyone wants to
see at a dignified or romantic ceremony.) Among hundreds of domestic pigeon breeds, most are hopeless navigators; for instance, the Birmingham roller excels at spectacular aerial backflips, and the tippler has extraordinary endurance—the record is twenty-two hours of continuous flight, circling its loft—but neither one is very good at orienting itself. Only one breed, the Racing Homer, is used for serious pigeon racing. Because homing appears to be partly inherited, breeders select the best individuals over many generations. Other birds, like Lockley’s shearwaters, also have the characteristic, but pigeons are the only birds trained by us to exploit it. Since we can lure them with food and shelter, pigeons make ideal study subjects, and they have taught us some surprising things.

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TO BE ABLE
to find their way home from an unfamiliar place, birds must carry a figurative map and compass in their brains. The map tells them where they are, and the compass tells them which direction to fly, even when they are released with no frame of reference to their loft.

Researchers have gone to great lengths to confirm that pigeons don’t merely memorize their outward trip. In one experiment, birds were transported in sealed containers filled with purified air, mounted on tilting turntables between coils that varied the magnetic field, and exposed to loud noises and flashes of light, so that, unlike a blindfolded person in the backseat of a taxi who might remember the twists and turns of the journey, they had no external cues. In another study, pigeons were anesthetized and unconscious during the outward trip. They still made it home, proving the existence of an intrinsic map and compass system.

The most basic map is visual. Birds have excellent sight and
use landmarks to navigate, just like us. Pigeons learn their local area during short training flights close to home. On longer flights, they have even been tracked following roads, making abrupt ninety-degree turns over intersections. When they are on familiar ground, pigeons use their surroundings as a giant map, just like we do.

It’s when the birds are over unfamiliar territory that things get really interesting. Because they don’t know the landmarks, they must use other, more refined methods of navigation—the inner compass. Unlike our compasses, birds use several methods to determine direction. If one method doesn’t work for some reason, they’ll switch to a backup.

Many birds orient based on the sun. In experiments, captive starlings exposed to a movable lamp in place of the sun shift their direction according to the position of the lamp. The sun moves, and birds compensate by the time of day. Starlings that have been artificially conditioned to a different day length, again using indoor lamps, also shift their direction when exposed to real sunshine and orient the wrong way. Pigeons may use the sun as their main compass, but they still make it home on cloudy days—so other, more advanced orientation techniques must kick in.

At night, some birds are able to navigate by the stars, apparently not by using specific constellations but by watching the rotation of the entire sky. When placed in a planetarium, buntings (a type of small songbird) orient themselves based on whatever star the sky revolves around, whether the North Star or a fictitious point. Many songbirds migrate at night, and this might help explain how they navigate after dark. Pigeons are diurnal and don’t do as well at night, when they’d rather sleep; they typically rest after the sun goes down and wait for dawn.
For this reason, most pigeon races are held during the day, in clear weather. But the birds do occasionally reach their home loft in the wee hours of the night, confirming that they can fly after dark if they have to.

Cover a pigeon’s eyes and it will probably still get home by using its other senses to navigate. One owner fitted his birds with frosted glasses and described them blindly “helicoptering down” out of the sky to reach their loft. In the 1970s, a series of experiments seemed to show that pigeons (as well as a variety of invertebrates and possibly other animals) can sense the linear polarization of sky light and thus interpret the sun’s position even on cloudy days, though the importance of polarization remains unclear. Even more interesting, researchers in Europe tried individually covering the eyes of migratory robins and found that the birds could navigate well without using the left eye but got lost when the right eye was blocked. The birds might be using some kind of photomagnetic receptors, processed by the left side of the brain, which has stronger ties with the right eyeball. In other words, the birds could “see” earth’s magnetic field, but only in one eye—a bizarre sense that humans can’t relate to at all.

There is plenty of evidence that pigeons and other birds use natural magnetic fields just like a traditional compass. How they detect the fields is up for debate—perhaps it’s the heavy iron content of cells in their inner ears or specialized receptors in their eyes—but robins have been shown to orient to powerful magnetized coils in captivity, although they can’t tell the difference between north and south, and other experiments have confirmed similar sensitivities. Recently, researchers have isolated groups of neurons in the brain stems of pigeons that become active according to the birds’ orientations in an
artificial magnetic field; the brain stem had been linked previously to activity in the inner ear. Again, we humans don’t share this sensitivity.

The map is harder to explain than the compass. How can a bird have a map of a place it has never visited? It must use a coordinate system. Pigeons may cue in to minute variations in the earth’s magnetic field to figure out their position on a worldwide grid, but nobody knows for sure. And recent experiments have raised other possibilities.

In one study, researchers isolated the nerves associated with magnetic receptors and sense of smell in the brain. Pigeons made it home just fine when their magnetic nerves were clipped, but they got lost when the nerves relating to smell were cut. Those pigeons apparently used an olfactory map of their environment, literally following their noses to get home. Though birds are usually said to lack a potent sense of smell, this idea is shifting; seabirds, particularly, are now known to find their nest burrows and even recognize their mates by smell alone, and others (like vultures) can pick up on minute concentrations of airborne particles. It’s possible that pigeons can sniff their way across the landscape much like a dog does.

In 2011, another group of researchers, in Italy, went a step further when they tested their idea that pigeons may rely on one nostril more than the other while navigating. They inserted rubber plugs into either the right or left nostril of thirty-one pigeons, attached global-positioning-system tags to their backs, and released the birds about twenty-six miles away from their home loft. The birds with their right nostril blocked took significantly more circuitous paths on their homeward journey. Olfactory information is processed in the left hemisphere of the pigeon brain, which connects more strongly to the right nostril, so it makes sense that the right side of their noses would
be critical if the birds used smell to navigate. This connection isn’t limited to birds, either; though humans, on average, can smell better with the left nostril than the right, we tend to find odors more pleasant when inhaled through the right nostril. The yoga breathing discipline of Swara holds that the right nostril is hot and solar, the left cool and lunar—you decide whether that might carry over to pigeons, but there does seem to be a measurable difference between the two sides of the nose.

The latest research also indicates that pigeons can sense infrasound, the low-frequency noise of the ocean and air currents, and orient themselves accordingly. These sound waves, below the range of human hearing (and near the frequency of earthquakes and whale songs), are so long that they pass through the ground, sometimes traveling hundreds of miles. They also change with atmospheric conditions, so the sounds may travel farther on some days than others. In the 1990s, one geologist speculated that the supersonic boom of the Concorde was interfering with pigeon races because the birds seemed to lose their way more often on clear days when the plane was flying. That was never confirmed, but it’s possible; a 2013 study from New York found that homing pigeons got lost on days when infrasound from their home loft didn’t reach the point where they were released. In other words, the birds needed to hear the sounds of home to get there.