Decoding the hidden world of non-human sound, with new biotechnology

The following is an excerpt from The sounds of life: how digital technology brings us closer to the world of animals and plants by Karen Bakker.

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The sounds of life: how digital technology brings us closer to the animal and plant worlds

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

The deepest infrasound is generated by our planet itself. If you could tune into Earth’s infrasound, you could hear the rumble of calving icebergs, the howl of a volcano, or the roar of a typhoon halfway around the world. Lowest of all, Earth’s periodic infrasonic pulse echoes beneath our feet and through the air. When ocean waves collide on continental shelves, they cause the earth’s crust to vibrate rhythmically – the heartbeat of our planet. When earthquakes shake the surface of our planet, they create airborne infrasonic tremors, ringing our atmosphere like a silent bell.

The infrasonic chorus of the planet constantly resonates all around you. Many animals—rock pigeons and snakes, tigers and mountain beavers—are able to hear these low-frequency sounds, but humans cannot. Our hearing is usually confined to a relatively narrow band of frequencies, between 20Hz and 20kHz, a range that narrows with age. At best, we can sometimes experience infrasound as a throbbing in the chest or an unsettling feeling of unease.

At the other end of the spectrum, above the upper threshold of human hearing, is ultrasound: 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 have already been able to hear these high-pitched sounds, and our smaller primate cousins ​​- tiny tarsiers and dwarf lemurs – can still communicate using ultrasound. But contemporary humans have lost this ability.

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Still other species use ultrasound to visualize their world: to navigate, find mates and track prey. Using what is called echolocation, bats and toothed whales create images of their surroundings by sending out beams of ultrasound and analyzing the echoes that return. Biosonar (as echolocation is also known) works much like an acoustic flashlight, evolved through evolution to be as accurate as our best medical devices. Simpler forms of echolocation are also used by cave swallows and oilbirds, night 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. Attentive humans can occasionally hear the subtle clicks at the lower end of the animal echolocation; rarely, blind people even develop the ability to echo themself. But for most of us, even the loudest ultrasonic sound blown didirectly to our ears would sound like nothing more than an empty, ghostly puff of wind.

As the Blackfoot philosopher Leroy Little Bear says, “The human brain is like a station on the dial of the radio; parked in one place, it is deaf to all other stations…animals, rocks, trees, simultaneously broadcasting across the spectrum of sensitivity. Our physiologies – and perhaps our psyches – limit our ability to listen to our nonhuman relatives. But humanity is beginning to develop its ability to hear. Digital technologies, so often associated with our alienation from nature, offer us the opportunity to listen to non-humans in powerful ways, rekindling our connection to the natural world.

In recent years, scientists have begun installing digital listening devices in almost 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. The researchers attached tiny microphones to bees and turtles, and attached listening posts to coral reefs and trees. When interconnected, these listening networks can span entire continents and ocean basins. Hobbyists are also listening to nature sounds, using inexpensive listening devices, such as the AudioMoth (an open-source device the size of a smartphone); the cheapest build-your-own version now costs well under $100. Combined, these digital devices work like a hearing aid on a planetary scale: allowing humans to observe and explore the sounds of nature beyond the limits of our own sensory abilities.

This book tells the stories of the scientists who use these digital technologies to decode the hidden world of non-human sound and the startling sounds they hear. Recent scientific breakthroughs have revealed that a vast array of species produce an astonishing assortment of sounds, most beyond the range of human hearing. until recently, unsuspected and misunderstood. (In writing this book, I researched over 1,000 species, a small fraction of scientific discoveries in bioacoustics – the technical term for the science of listening to non-human organisms.) Dolphins and beluga whales, mice and prairie dogs use unique vocalizations (like characteristic whistles) to refer to each other, much like we do with individual names. Baby bats “babble” about their mothers, who respond to their young in “mother tongue”, just like humans do. Turtle hatchlings, once thought to be mute, coordinate the timing of their birth by calling to each other through their shells. Animals use sound to warn, protect and attract each other; to learn, have fun and name.

Close listening to the non-human world reveals complex communication across a wide range of species and challenges the claim that humanity alone uniquely possesses language. These claims may seem plausible when dealing with primates or birds. But what digital technologies are revealing is the vast expanse of sound communication across the natural world. Using computational bioacoustics, scientists have documented the ability of species without ears, or any apparent means of hearing, to interpret and respond to complex information transmitted through sound. When scattered 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, then return home to install. Plants emit distinct ultrasounds when they are dehydrated or in distress. In response to the buzzing of bees, the flowers flood with sweet nectar, as if in anticipation. The Earth is in continuous conversation. Today, digital technologies offer humanity a new way to listen to the living soundscapes around us, opening our ears to the resonant mystery of non-human sound.

Extract of The sounds of life: how digital technology brings us closer to the animal and plant worlds. Copyright © 2022 by Karen Bakker. Reprinted with permission from Princeton University Press.

Meet the writer

Karen Bakker

About Karen Bakker

Karen Bakker is a researcher in digital innovation and environmental governance, professor and author ofThe sounds of life: how digital technology brings us closer to the world of animals and plants.

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