How Animals Perceive the World

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Below is an excerpted article from The Atlantic written by Ed Yong whose new book An Immense World: How Animal Senses Reveal the Hidden Realms Around Us is available now.

Every animal is enclosed within its own sensory bubble, perceiving but a tiny sliver of an immense world. There is a wonderful word for this sensory bubble—Umwelt. It was defined and popularized by the Baltic German zoologist Jakob von Uexküll in 1909. Umwelt comes from the German word for “environment,” but Uexküll didn’t use it to refer to an animal’s surroundings. Instead, an Umwelt is specifically the part of those surroundings that an animal can sense and experience—its perceptual world. A tick, questing for mammalian blood, cares about body heat, the touch of hair, and the odor of butyric acid that emanates from skin. It doesn’t care about other stimuli, and probably doesn’t know that they exist. Every Umwelt is limited; it just doesn’t feel that way. Each one feels all-encompassing to those who experience it. Our Umwelt is all we know, and so we easily mistake it for all there is to know. This is an illusion that every creature shares.

Humans, however, possess the unique capacity to appreciate the Umwelten of other species, and through centuries of effort, we have learned much about those sensory worlds. But in the time it took us to accumulate that knowledge, we have radically remolded those worlds. Much of the devastation that we have wrought is by now familiar. We have changed the climate and acidified the oceans. We have shuffled wildlife across continents, replacing indigenous species with invasive ones. We have instigated what some scientists have called an era of “biological annihilation,” comparable to the five great mass-extinction events of prehistory. But we have also filled the silence with noise and the night with light. This often ignored phenomenon is called sensory pollution—human-made stimuli that interfere with the senses of other species. By barraging different animals with stimuli of our own making, we have forced them to live in our Umwelt. We have distracted them from what they actually need to sense, drowned out the cues they depend upon, and lured them into sensory traps. All of this is capable of doing catastrophic damage.

Photo by Diana Parkhouse

In 2001, the astronomer Pierantonio Cinzano and his colleagues created the first global atlas of light pollution. They calculated that two-thirds of the world’s population lived in light-polluted areas, where the nights were at least 10 percent brighter than natural darkness. About 40 percent of humankind is permanently bathed in the equivalent of perpetual moonlight, and about 25 percent constantly experiences an artificial twilight that exceeds the illumination of a full moon. “‘Night’ never really comes for them,” the researchers wrote. In 2016, when the team updated the atlas, it found that the problem had become even worse. By then, about 83 percent of people—including more than 99 percent of Americans and Europeans—were under light-polluted skies. More than a third of humanity, and almost 80 percent of North Americans, can no longer see the Milky Way. “The thought of light traveling billions of years from distant galaxies only to be washed out in the last billionth of a second by the glow from the nearest strip mall depresses me to no end,” the visual ecologist Sönke Johnsen once wrote.

At Colter Bay, Cole flips the lights from red back to white and I wince. The extra illumination feels harsh and unpleasant. The stars seem fainter now. Sensory pollution is the pollution of disconnection. It detaches us from the cosmos. It drowns out the stimuli that link animals to their surroundings and to one another. In making the planet brighter and louder, we have endangered sensory environments for countless species in ways that are less viscerally galling than clear-cut rain forests and bleached coral reefs but no less tragic. That must now change. We can still save the quiet and preserve the dark.

Every year on September 11, the sky above New York City is pierced by two columns of intense blue light. This annual art installation, known as Tribute in Light, commemorates the terrorist attacks of 2001, with the ascending beams standing in for the fallen Twin Towers. Each is produced by 44 xenon bulbs with 7,000-watt intensities. Their light can be seen from 60 miles away. From closer up, onlookers often notice small flecks, dancing amid the beams like gentle flurries of snow. Those flecks are birds. Thousands of them.

This annual ritual unfortunately occurs during the autumn migratory season, when billions of small songbirds undertake long flights through North American skies. Navigating under cover of darkness, they fly in such large numbers that they show up on radar. By analyzing meteorological radar images, Benjamin Van Doren showed that Tribute in Light, across seven nights of operation, waylaid about 1.1 million birds. The beams reach so high that even at altitudes of several miles, passing birds are drawn into them. Warblers and other small species congregate within the light at up to 150 times their normal density levels. They circle slowly, as if trapped in an incorporeal cage. They call frequently and intensely. They occasionally crash into nearby buildings.

Migrations are grueling affairs that push small birds to their physiological limit. Even a night-long detour can sap their energy reserves to fatal effect. So whenever 1,000 or more birds are caught within Tribute in Light, the bulbs are turned off for 20 minutes to let the birds regain their bearing. But that’s just one source of light among many, and though intense and vertical, it shines only once a year. At other times, light pours out of sports stadiums and tourist attractions, oil rigs and office buildings. It pushes back the dark and pulls in migrating birds.

In 1886, shortly after Thomas Edison commercialized the electric light bulb, about 1,000 birds died after colliding with illuminated towers in Decatur, Illinois. More than a century later, the environmental scientist Travis Longcore and his colleagues calculated that almost 7 million birds die each year in the United States and Canada after flying into communication towers. The lights of those towers are meant to warn aircraft pilots, but they also disrupt the orientation of nocturnal avian fliers, which then veer into wires or each other. Many of these deaths could be avoided simply by replacing steady lights with blinking ones.

Mareks Steins

“We too quickly forget that we don’t perceive the world in the same way as other species, and consequently, we ignore impacts that we shouldn’t,” Longcore tells me in his Los Angeles office. Our eyes are among the sharpest in the animal kingdom, but their high resolution comes with the cost of low sensitivity. Unlike most other mammals, our vision fails us at night, so we crave more nocturnal illumination, not less.

So is true silence.

It’s a sunny April morning in Boulder, Colorado, and I’ve hiked up to a rocky hillside, about 6,000 feet above sea level. The world feels wider here, not just because of the panoramic view over conifer forests but also because it is blissfully quiet. Away from urban ruckus, quieter sounds become audible over greater distances. On the hillside, a chipmunk is rustling. Grasshoppers snap their wings together as they fly. A woodpecker pounds its beak against a nearby trunk. Wind rushes past. The longer I sit, the more I seem to hear.

Two men puncture the tranquility. I can’t see them, but they’re somewhere on the trail below, intent on broadcasting their opinions to all of Colorado. Then I realize I can also hear faraway vehicles zooming along a highway beyond the trees. Denver hums in the distance, an ambient backdrop that I had all but blocked out. I notice the roaring engines of a plane flying overhead. After my hike, I meet up with Kurt Fristrup, who says he’s been backpacking since the mid-1960s. In that time, aircraft emissions have increased nearly sevenfold. “One of my favorite parlor tricks when friends visit is to ask, at the end of the hike, if they heard any aircraft,” he tells me. “People will say they remember one or two. And I’ll say there were 23 jets and two helicopters.”

Before he retired, Fristrup was a scientist at the National Park Service’s Natural Sounds and Night Skies Division, a group that works to safeguard (among other things) the United States’ natural soundscapes. To protect them, the team first had to map them, and sound, unlike light, can’t be detected by satellites. Fristrup and his colleagues spent years lugging recording equipment to almost 500 sites around the country, capturing nearly 1.5 million audio samples. They found that human activity doubles the background-noise levels in 63 percent of protected spaces like national parks, and increases them tenfold in 21 percent. In the latter places, “if you could have heard something 100 feet away, now you can only hear it 10 feet away,” Rachel Buxton, a former National Park Service research fellow, told me. Aircraft and roads are the main culprits, but so are industries like oil and gas extraction, mining, and forestry, which fill the air with drilling, explosions, engine noises, and the thud of heavy tires. Even the most heavily protected areas are under acoustic siege.

In towns and cities, the problem is worse, and not just in the United States. In 2005, two-thirds of Europeans were immersed in ambient noise equivalent to perpetual rainfall. Such conditions are difficult for the many animals that communicate through calls and songs. Scientists have found that noisy neighborhoods in Leiden, in the Netherlands, compel great tits to sing at higher frequencies so that their notes don’t get masked by the city’s low-pitched hubbub. Nightingales in Berlin are forced to belt out their tunes more loudly to be heard over the surrounding din. Urban and industrial noise can also change the timing of birds’ songs, suppress the complexity of their calls, and prevent them from finding mates. Noise pollution masks not only the sounds that animals deliberately make but also the “web of unintended sounds that ties communities together,” Fristrup says. He means the gentle rustles that tell owls where their prey is, or the faint flaps that warn mice about impending doom.

To perceive the world through others’ senses is to find splendor in familiarity, and the sacred in the mundane.

To truly make a dent in sensory pollution, bigger steps are needed. Lights can be dimmed or switched off when buildings and streets are not in use. They can be shielded so that they stop shining above the horizon. LEDs can be changed from blue or white to red. Quiet pavements with porous surfaces can absorb the noise from passing vehicles. Sound-absorbing barriers, including berms on land and air-bubble curtains in the water, can soften the din of traffic and industry. Vehicles can be diverted from important areas of wilderness, or they can be forced to slow down: In 2007, when commercial ships in the Mediterranean began slowing down by just 12 percent, which saves fuel and reduces emissions, they produced half as much noise. Such vessels can also be fitted with quieter hulls and propellers, which are already used to muffle military ships (and would make commercial ones more fuel-efficient).

We could regulate industries causing sensory pollution, but there’s not enough societal will. “Plastic pollution in the sea looks hideous and everyone is worried, but noise pollution in the sea is something we don’t experience so directly, so no one’s up in arms about it,” Lamont says. And as we desecrate sensory environments, we grow accustomed to the results. Our blinding, blaring world becomes normal, and pristine wilderness feels more distant.

But the majesty of nature is not restricted to canyons and mountains. It can be found in the wilds of perception—the sensory spaces that lie outside our Umwelt and within those of other animals. To perceive the world through others’ senses is to find splendor in familiarity, and the sacred in the mundane. Wonders exist in a backyard garden, where bees take the measure of a flower’s electric fields, leafhoppers send vibrational melodies through the stems of plants, and birds behold the hidden palettes of ultraviolet colors on their flock-mates’ feathers. Wilderness is not distant. We are continually immersed in it. It is there for us to imagine, to savor, and to protect.

In 1934, after considering the senses of ticks, dogs, jackdaws, and wasps, Jakob von Uexküll wrote about the Umwelt of the astronomer. “Through gigantic optical aids,” he wrote, this unique creature has eyes that “are capable of penetrating outer space as far as the most distant stars. In its Umwelt, suns and planets circle at a solemn pace.” The tools of astronomy can capture stimuli that no animal can naturally sense—X-rays, radio waves, gravitational waves from colliding black holes. They extend the human Umwelt across the universe and back to its very beginning. The tools of biologists are more modest in scale, but they, too, offer a glimpse into the infinite. Scientists have used night-vision goggles to show that nocturnal bees can see in extreme darkness, clip-on microphones to eavesdrop on the vibrational songs of leafhoppers, and electrodes to listen in on the pulses of electric fish. With microscopes, cameras, speakers, satellites, and recorders, people have explored other sensory worlds. We have used technology to make the invisible visible and the inaudible audible.

No creature could possibly sense everything, and no creature needs to. Evolving according to their owner’s needs, the senses sort through an infinity of stimuli, allowing through only what is relevant. To learn about the rest is a choice. The ability to dip into other Umwelten is our greatest sensory skill. A moth will never know what a zebra finch hears in its song, a zebra finch will never feel the electric buzz of a black ghost knifefish, a knifefish will never see through the eyes of a mantis shrimp, a mantis shrimp will never smell the way a dog can, and a dog will never understand what it is like to be a bat. We will never fully do any of these things either, but we are the only animal that can try. Through patient observation, through the technologies at our disposal, through the scientific method, and, above all else, through our curiosity and imagination, we can try to step into perspectives outside our own. This is a profound gift, which comes with a heavy responsibility. As the only species that can come close to understanding other Umwelten, but also the species most responsible for destroying those sensory realms, it falls on us to marshal all of our empathy and ingenuity to protect other creatures, and their unique ways of experiencing our shared world.

Header photo by Marek Piwnicki on Unsplash

This article has been adapted from Ed Yong’s latest book, An Immense World: How Animal Senses Reveal the Hidden Realms Around Us. It appears in the July/August 2022 print edition with the headline “Our Blinding, Blaring World.”


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