CHAPTER THREE
The Organized Sound of
Life Itself
It was my third day at the late Dian Fossey’s camp in Karisoke, Rwanda—a remote place where one quickly acclimates to contact with the nonhuman animal world. At that time, a few years before the political turmoil that devastated the country in the 1990s, some protected biomes in the Virunga Mountains—despite occasional poaching and deforestation pressure—existed at a high level of viability, and still do today.
When I visited in 1987, the mountain gorillas had begun to slowly increase in numbers, and poaching in general had enjoyed a period of moderation, with the sometimes uneasy truce between government and outside agencies such as Fossey’s Digit Fund. I was eager to be in that world, and a couple of hours into a short, half-day orientation, my ADHD kicked in and I convinced myself that I had absorbed all I needed to know about the rhythms of the forest creatures. Most notably, I thought, I had sufficiently learned to avoid the danger of contact with forest elephants and Cape buffalo, and how to behave around the gorillas.
Confidently secure in my new knowledge, I assured the other researchers and guides that I knew the field protocol and could be left alone with the study animals and my gear. They went off to do their own observations, and I sat quietly in one spot. Juvenile mountain gorillas played all around me as the adults tenderly groomed one another, resting between periods of daytime foraging while constantly reassessing the status of male hierarchies.
It was obvious by the look of the vegetation that there had been a fight. Torn up bamboo and scrub lay all around, and the general soundscape—filled with a combination of nearby shrikes, bulbuls, cuckoos, parrots, turacos, orioles, flycatchers, and multiple insect species—telegraphed a palpable tension, as did the pungent scent of the alpha male and the body language of the other apes. The richly defined soundscape of the Virungas had left an initial impression, but it soon became apparent that I had missed some subtle yet crucial signals provided by the location’s fabric of animal voices. In a fraction of a second, the avian section of the chorus became tentative and quiet. Many of the insects abruptly stopped stridulating. A hush came over the forest, as if it were trying to avoid involvement with something that was about to happen. At the edge of my field of vision, almost behind me, I could just see the juvenile male Pablo as he crouched, skulking some distance from the others—partially hidden in a cluster of dense vegetation. Evidently he had been caught trying to mate with one of Ziz’s favorite females, and Ziz, the alpha male of the group, had battered Pablo with the clear intention of reminding him who was in charge.
My stereo microphones were mounted on top of my San Francisco Giants baseball cap, and my recorder was running. Unfamiliar with the individual characters, I had absentmindedly positioned myself between Pablo and Ziz. And then I missed another important shift in the intensity of the surrounding bioacoustic fabric—something I might have caught had I been more present. It wasn’t until later, when listening to a playback of the tape, that I recognized the signal’s message.
Quite literally out of nowhere, a quick succession of chest beats from one of the apes broke the spell of the remaining ethereal ambience. Because stereo signals only reveal right and left perspectives in a set of earphones, I was only capable of perceiving sound sources coming from either side of the acoustic field. Pablo, really pissed, hammered out a rapid-fire exchange on his thorax with cupped fists, like a series of rim shots on a snare drum. There was a deafening scream and an explosive crash of vegetation as he cleared a path between himself and his more dominant rival—altogether an overwhelming sonic burst that overloaded my recording. It was impossible to tell that the terrifying uproar was coming from behind and rapidly getting closer. While others in the area obligingly got out of the way, I remained seated, awkwardly weighed down with more than forty pounds of equipment. Then a massive, hairy black hand tightly gripped my right shoulder. In one effortless motion, Pablo picked me up—recorder, backpack, and all—and flung me fifteen feet through the air in a blur of sky, vegetation, and whooshing Gore-Tex. The flash of weightlessness ended when I landed facedown on top of my equipment in a patch of stinging nettles, gasping for air that had been knocked out of my system. My body and recorder somewhat unscathed, I was lucky to walk away. All the warning signs were there, had I known to listen more attentively.
• • •
When I was growing up in Detroit, and my parents and their friends and family listened—really listened—to something that was outside the ritual buzz of their daily lives, they mostly turned to music. And, when I was present, they usually chose forms within a very narrow range of expression deemed appropriate for young, impressionable ears, a rather pretentious mix of the classics and a wee bit of jazz. Tolerated but never really acknowledged were all the extraneous noises that also penetrated our environment.
So with either certain kinds of music or irksome noise as my early listening template, imagine my sense of wonder when I discovered for myself—lying alone in my room during those spring and summer evenings—that all the living organisms outside my window were singing melodies that merged into parts of a much larger choir. The joy was a secret that I was certain no one else would understand.
It was only a good deal later that I recognized all living organisms generated a unique sound signature. For instance, when viruses let go from a surface they’ve been attached to, they create a detectable sonic spike—a sharp, quick change in amplitude measurable by only the most sensitive instruments. Then there are the low-frequency moans and clicks—far below what humans can detect unaided—of the largest living animal on the planet, the blue whale.
For one of my first jobs in Hollywood, I was hired as part of a sound crew during the filming of a B movie. Trying to encourage me to quit, the film director exiled me to Iowa in August and charged me with recording the sound of corn growing. He wanted me off the set, he explained, because he didn’t need two sound recordists and, as I was working under union contract, I couldn’t actually be fired. So off I went, ever dutiful and on a mission. Like Brer Rabbit in the briar patch, I obediently sat in the middle of a cornfield about fifty miles west of Des Moines all night long with my microphone held up to a stalk of corn, waiting for some event to occur—I had no idea what. It turns out that corn makes a sound as it expands telescopically, the staccato-like clicks and squeaks reminiscent of rubbing dry hands in quick, jerky movements across the surface of a well-inflated rubber party balloon. The sound of corn growing.
And the sounds little things make! The first time I heard ants “sing,” I was nearly fifty years old. I was speechless for hours. Ants “sing” by stridulating—rubbing their legs across their abdomens. While working on a project in the American Southwest desert, my team and I were filmed by National Geographic as we recorded fire ants attempting to remove a pair of small lavalier microphones I had placed over the entrance to their nest. The ants’ actions—the command signals to workers to remove the impediment from the entrance—were communicated entirely by sound.
I’ve often heard people say that the voice of a creature depends on its size—that small creatures have tiny, soft voices, while larger animals are somehow louder. But careful listening will quickly explode this myth. The Pacific tree frog outside my bedroom window is about the size of my little fingernail. Its voice can be heard more than a hundred yards away. One evening this spring, it registered 80 dBA at ten feet! Baby vultures in the forests of Ecuador have bodies so small that they would fit neatly in the palm of your hand, yet their roar is so loud and fierce that it would be great in a horror movie. On the other hand, many large animals have relatively soft voices—for example, the giraffe (except for its low-frequency sounds), the California gray whale, the tapir, the capybara, and the anteater. When it comes to natural sounds, there are few rules. Our preconceptions are almost always trumped by the incredible diversity of life on earth.
Anemones produce unusual sounds, although we have no idea how or why o
r what the sound might mean to other organisms in the vicinity. On a soundscape trip around Southeast Alaska, my group found a tide pool filled with barnacles, rockfish fry darting from place to place to hide, small crabs, clams, and some brilliantly colored anemones. One, whose mouth part (the center cavity) had grown to nearly five inches in diameter, looked particularly inviting for an experiment. I gently lowered a hydrophone into the cavity. Immediately the fleshy core of the creature sucked the instrument deep into its middle while the tentacles engulfed the rest of the object, searching for something of nutritional value. Finding none, the anemone expelled the hydrophone with a couple of loud, obscene grunts. If anemones create sounds, what about other creatures we’ve overlooked?
For instance, why would insect larvae create sound signatures? Some do. In marine environments, where many larvae appear to vocalize, is there already a climate of competition at such an early stage?
What would motivate hippos to vocalize underwater, and how close are those utterances to those of some species of whales? In muddy river environments, it’s important to remain in contact with other members of the bloat. Like gray whales, hippos are social animals that like to stay in contact, producing similar grunts and other sounds.
What causes giraffes, until very recently thought to be rather quiet, to vocalize in frequencies so low that we can’t hear them with our ears alone? Is that the only bandwidth in the biophonic structure open to them? Are they taking advantage of an empty channel so that their voices can be heard by other giraffes?
Generally we have only partial answers to questions like these and are just now realizing that we have much to gain by listening critically to the natural sounds of the earth and its nonhuman inhabitants. When I’m in the field observing animals up close, I try to imagine what they hear, and how the shapes of their ears might collect sound. I want to know how they perceive acoustic information. Cup your hands behind your ears and slowly turn around. The sounds gathered by the ear extensions make the sound appear louder and more focused. You’ll hear more because your ears just got bigger.
Once, while working in Sumatra, I watched amazed as a rarely seen clouded leopard circled right in front of where I was sitting, changing the direction of its ears every few seconds, then directing them straight ahead to where it was looking. I went back to our campsite and cut out some paper ears that were similar in shape to the pinnas (outer ears) of the leopard. Then I mounted a pair of small microphones on them and clipped each ear to the stems of my glasses. The difference between what I heard with my ears alone and with the faux cat’s ears was impressive. I tried to listen as might some animals with proportionally large ears—such as bats, many felids (cats), and canids (foxes, wolves, coyotes, dingoes, jackals, and others)—and to understand how ear shapes and sizes help creatures locate the direction from which a sound comes and make out its nuances. Increasing the size of the sound-gathering pinnas greatly enhanced the detail of what I heard and recorded. Bird and insect sounds were brought into much closer range, and the acoustic features were much sharper. Watch how a cat navigates by sound, catching every detail with focused attention by controlling the aim of each ear or both ears together. Make a pair of cat-shaped ears for yourself. You’ll get the idea.
The way an animal detects sound depends on the specific creature, its habitat, and what it has evolved to listen for. Complex listening is one of the few operations that advanced life forms can do simultaneously with other functions—the organisms interpret information that conveys complex data, can change the coding of the signal instantaneously, and perform other tasks such as determining the usefulness of the received information relative to aspects of their survival.
At first, when their numbers were relatively small, acoustically sensitive organisms merely needed to filter out the geophonic background in order to perceive other sound-producing organisms within their habitats. As the number of species increased and became more complex, they had to be able to hear and process the particular sounds that were relevant to their well-being. Over the course of many glacial periods, especially the recent ones, the total number of creatures multiplied exponentially—species filling available biological niches. Complex habitats arose that supported robust varieties of life-forms whose behavior and survival—both individually and collectively—were determined to a large extent not only by visual, olfactory, and tactile cues but by sound.
The mechanisms for hearing vary from species to species—and they depend, of course, on whether the creature lives on land or in water. Many fish, for instance, detect changes in pressure through the lateral line, a bundle of nerve cells that stretches from the gill to the tail, usually about midway between the dorsal and pectoral fins. When schools of fish suddenly veer off in one direction or another as a group, they are responding to pressure waves that strike their individual lateral lines at the same time.
Terrestrial mammals share to some degree consistently developed ear structures across species. Their ears consist of an outer ear, or pinna, as well as a middle ear, which is the air cavity behind the eardrum that includes the stapes, anvil, and malleus, or hammer. Sound—a wave of pressure traveling through the air—causes the eardrum to vibrate. The structures in the middle ear transfer these vibrations to the fluid-filled inner ear. Within the inner ear is the cochlea, which contains hair cells—cells with protruding hairlike structures that determine the frequency range the listener will be sensitive to. Some groups of cells are more sensitive to low-frequency signals, while others specialize in the higher end of the spectrum. Hair cells serve as both detectors and amplifiers—the motion of the cells is converted into signals that are transmitted from nerve to nerve until they reach the brain and are processed into useful information.
In marine mammals, however, because there is no need to create an impedance match with air, there is also no need for an intermediate organ—the marine mammals’ physical structure allows sound to be detected in the throat, which is then directly conveyed to the inner ear. Some toothed whales, such as dolphins, actually perceive sound through their jaws. The common seal can detect sound through its vibrissae, or whiskers—shorter ones pick up higher frequencies; longer ones, lower signals.
Insects detect sound in one of three ways: Some—such as crickets, grasshoppers, and cicadas—sport a kind of eardrum that is exposed to the air and that can be located, depending on the species, anywhere from the thorax to the front legs. Others hear through tiny hairs—called a Johnston’s organ—that reside on their antennae. Then there are insects such as hawk moths that can detect, through a hearing-specific organ on their heads, the incoming 50 kHz to 70 kHz echolocation signals of bats seeking them out as meals. (And some nonsinging insects, such as the mountain pine beetle, don’t hear at all, although they are likely to sense vibrations transmitted through the ground, air, trees, or other vegetation.)
Reptiles, in general, have a tympanic membrane that is either visible on the surface of the skin or slightly recessed. It’s connected directly to the middle ear, which in turn transmits vibrations to the inner ear and then on to the brain. Crocodiles produce and receive very low-frequency sounds, suggesting that this so-called infrasound is detected by their half-submerged bodies. Like reptiles, frogs perceive sound through an external tympanic membrane located directly behind their eyes. And also like many reptiles, they probably pick up vibrations through the ground and water as well. Many times, as I’ve silently tried to approach the shore of a pond, frogs sitting on a log will detect the motion either visually or through the ground transmission of my advancing footsteps, and will quickly disappear into the water or shoreline grasses.
Except for owls, which have the highly developed hearing and sound-processing skills necessary for sonically locating prey in dim light and dense habitats, birds don’t have obvious ears. But they do have ear holes in their heads, which are located just below their eyes and are covered with feathers. This makes sense: wind noise (in flight or even while roosting) can cause interference wit
h reception, and feathers help mediate the problem. Aside from lacking pinnas, a bird’s hearing mechanism is remarkably similar to that of a human. In fact, most birds hear within the same frequency range as humans, but the way they process sound is geared to the intricacies of the songs and calls of their own species.
Animals handle sound in enough ways to fill multiple books on that subject alone. There is a gopher that burrows under the surface of our vegetable garden, nibbling at the tender roots of our organic plantings. It will pay no attention to the sounds of our cat’s padded footfalls or swishing tail raking over the ground—but it sure as hell will respond to the slithering vibrations of the five-foot gopher snake that lurks about, seeking openings to the gopher’s subterranean labyrinth. The mule-deer doe and its twin fawns that graze alongside our country road each evening are unresponsive to the sound of our car as it slowly drives by. But if I am on foot, approaching them from a hundred yards away, they’ll quickly bolt into the woods and out of sight. Even though this is a hunt-free zone, there must be something in their acoustic DNA that signals to them: “Humans on foot mean serious danger.” But the reassuring sound of a passing automobile—as long as it doesn’t stop—registers little or no consequence.
The ultrasound signals produced by bats and toothed whales—such as dolphins, killer whales, and sperm whales—are used to send and receive information related to echolocation. These high-pitched bursts of sound, from around 18 kHz to in excess of 200 kHz, are thought to provide imaging not unlike the ultrasound scan machines used in the medical profession. Some of these creatures receive an acoustic image of an object so detailed that they can distinguish between two quarter-size coins, one made of wood and the other of plastic, from twenty-five yards away underwater.
The Great Animal Orchestra Page 6