Decoding The Hidden World Of Nonhuman Sound, With New Biotech

The following is an excerpt from of The Sounds of Life: How Digital Technology Is Bringing Us Closer to the World of Animals and Plants by Karen Bakker.

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The Sounds of Life: How Digital Technology Is Bringing Us Closer to the Worlds of Animals and Plants

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Compared with our cousins on the Tree of Life, humans are poor listeners. Below the lower end of human hearing lies deep infrasound: the realm of thunder and tornadoes, elephants and whales. Many creatures can sense and communicate in infrasound, which travels long distances with ease, passing through air and water, soil and stone. In one of the animal kingdom’s most famous mating rituals, male peacocks transmit powerful infrasound with their raised tails; what humans perceive to be a visual display is, in fact, a sonic summons.

The deepest infrasound is generated by our planet itself. If you could tune into the Earth’s infrasound, you might hear the rumblings of calving icebergs, the howl of a volcano, or the roar of a typhoon halfway around the world. Lowest of all, the Earth’s periodic infrasonic pulse resonates below our feet and through the air. As ocean waves collide over continental shelves, they vibrate the Earth’s crust in a rhythmic fashion—the drumming heartbeat of our planet. When earthquakes convulse our planet’s surface, they create airborne infrasonic tremors—ringing our atmosphere like a quiet bell.

The planet’s infrasonic chorus is continuously sounding all around you. Many animals—rock doves and snakes, tigers and mountain beavers—are able to hear these low-frequency sounds, but not humans. Our hearing is typically confined to a relatively narrow band of frequencies, between 20 Hz and 20 kHz, a range that narrows as we age. At best, we can sometimes sense infrasound as a throbbing in the chest, or a troubling feeling of unease.

At the other end of the spectrum, above the upper threshold of human hearing, lies the ultrasonic: high-frequency sounds that vibrate too quickly for us to hear. A surprisingly diverse array of species—mice and moths, bats and beetles, corn and corals—emit ultrasonic sounds imperceptible to humans. Our ancestors may once have been able to hear these high-pitched sounds, and our smaller primate cousins—tiny tarsiers and dwarf lemurs—can still communicate in ultrasound. But contemporary humans have lost this ability.

Still other species use ultrasound to visualize their world: to navigate, find mates, and follow prey. By using what is known as echolocation, bats and toothed whales create images of their surroundings by sending out beams of ultrasound and analyzing the returning echoes. Biosonar (as echolocation is also known) functions somewhat like an acoustic flashlight, honed by evolution to be as accurate as our finest medical devices. Simpler forms of echolocation are also used by cave swiftlets and oil birds, nocturnal shrews and rats; they, too, see the world through sound. Yet although these calls are some of the loudest ever recorded in the animal kingdom, they are inaudible to us. Attuned humans can occasionally hear the subtle clicks at the lower end of animal echolocation; rarely, blind people even develop the ability to echorange themselves. But for most of us, even the loudest ultrasonic sound blown directly into our ears would feel like nothing more than an empty, ghostly breath of wind.

As Blackfoot philosopher Leroy Little Bear says, “The human brain is like a station on the radio dial; parked in one spot, it is deaf to all the other stations… the animals, rocks, trees, simultaneously broadcasting across the whole spectrum of sentience.” Our physiologies—and perhaps our psyches—limit our capacity to listen to our nonhuman kin. But humanity is beginning to expand its hearing ability. Digital technologies, so often associated with our alienation from nature, are offering us an opportunity to listen to nonhumans in powerful ways, reviving our connection to the natural world.

In recent years, scientists have begun installing digital listening devices in nearly every ecosystem on the planet, from the Arctic to the Amazon. These microphones are computerized, automated, and networked with digital sensors, drones, and satellites so powerful they can hear a mother whale whispering to her calf in the depths of the ocean. Researchers have attached tiny microphones to honeybees and turtles, and affixed listening posts to coral reefs and trees. When interconnected, these listening networks may stretch across entire continents and ocean basins. Amateurs are also listening to nature’s sounds, using inexpensive listening devices, like the AudioMoth (an open-source device the size of a smartphone); the cheapest build-it-yourself version now costs well under $100. Combined, these digital devices function like a planetary-scale hearing aid: enabling humans to observe and study nature’s sounds beyond the limits of our own sensory capabilities.

This book tells the stories of the scientists who are using these digital technologies to decode the hidden world of nonhuman sound, and the surprising sounds they are hearing. Recent scientific breakthroughs have revealed that a vast array of species makes an astonishing assortment of sounds, mostly beyond the range of human hearing—and so, until recently, unsuspected and unappreciated. (In writing this book, I surveyed research on more than 1,000 species, a small fraction of the scientific findings on bioacoustics—the technical term for the science of listening to nonhuman organisms.) Dolphins and belugas, mice and prairie dogs use unique vocalizations (like signature whistles) to refer to one another, much as we do with individual names. Baby bats “babble” at their mothers, who speak back to their young in “motherese,” just like humans do. Turtle hatchlings—previously thought to be mute—coordinate the moment of their birth by calling to one another through their shells. Animals use sound to warn, protect, and lure one another; to teach, amuse, and name one another.

Carefully listening to the nonhuman world reveals complex communication in a broad range of species and challenges the claim that humanity, alone, uniquely possesses language. These claims might seem plausible when discussing primates or birds. But what digital technologies reveal is the vast extent of sonic communication across the natural world. Using digital bioacoustics, scientists have documented the ability of species without ears, or any apparent means of hearing, to interpret and respond to complex information conveyed through sound. When dispersed in the open ocean, fish and coral larvae (creatures only a few millimeters in size, with no central nervous system) distinguish the sounds of their home reefs from the cacophonous ocean, and then swim back home to settle. Plants emit distinct ultrasonic noises when dehydrated or distressed. In response to the sound of buzzing bees, flowers flood with sweetened nectar, as if in anticipation. The Earth is in continuous conversation. Now, digital technologies provide a new way for humanity to listen to the vivid soundscapes all around us, opening our ears to the resonant mystery of nonhuman sound.

Excerpted from The Sounds of Life: How Digital Technology is Bringing Us Closer to the Worlds of Animals and Plants. Copyright © 2022 by Karen Bakker. Reprinted by permission of Princeton University Press.