The physiological systems that have evolved to receive sound are only the first stage in the hearing process. The organism must then decode the received signals into something of value—an acoustically sensitive creature’s life depends on being able to interpret the slightest nuances of complex acoustic information to determine if the environment is safe or if danger is imminent.
Like all sentient beings that sonically navigate through the world, we, too, receive a range of signatures. Some contain useful information that we call signal; some feature unwanted and unrelated sound fragments we call noise. Most sound that reaches our ears, of course, contains a mixture of both signal and noise. Those of us from industrial societies are so inexperienced when it comes to listening to the voices of the wild natural that we tend to miss the indicators that tell us about events taking place within earshot. If we knew how to read the exacting signs that inform the acoustic narrative, we might have a better sense of the dynamic energy of each habitat. Sometimes, though, the signs are not so subtle at all.
Most of us hear the sound of crickets, katydids, frogs, or various insects as a cacophony or din of noise. It is much harder to filter out useful information within these clusters. But when you listen closely you begin to discern a wealth of data from sound-producing creatures. When neighborhood kids come by during summer evenings, I like to play a game with them. “Anyone know how crickets tell us the temperature?” I ask.
The tempo of the stridulation—or number of pulses in any given period—is based on the ambient temperature, which affects the body temperature of the cold-blooded crickets. As we begin to listen more carefully, most of us realize that when hot days begin to cool down, the pulses the crickets produce are not synchronous. Crickets generate sound by rubbing their wings together, stridulating like the singing ants I described earlier. One cricket wing has a scraper, the other a file. Sound occurs when the wing containing the scraper rubs against the wing with the file. The crickets are inconsistent with the timing of their chirps because ground temperatures vary depending on where the cricket is located within the local territory. Shadier areas run cooler than those that have been in direct sun, so crickets in cooler areas chirp at a slower rate than those in hotter ones. Eventually, as the evening progresses, temperatures on the ground even out, and all the crickets perform their wing rubbing in phase—that is, perfectly synchronized.
You can actually determine the temperature by counting the number of chirps made by certain crickets. With the snowy tree cricket, for example, you can count the number of chirps that occur in fifteen seconds, add forty to the number, and arrive at the temperature in degrees Fahrenheit. Other species have different formulas that are just as easy to calculate (i.e., you can add the number of pulses that occur in fifteen seconds to a prescribed number, depending on the species).
A few years after my Rwanda assignment, soundscape commissions took me to Australia and southern Ecuador, where I came in contact with the still-ancient soundscapes of the Pitjantjatjara’s and Jivaro’s habitats, respectively. The Pitjantjatjara live in the deserts of Central Australia and move through what appears to an outsider as flat and undifferentiated terrain. As a result, one thinks they’d rely more on visual than on aural cues. But their world is characterized to a significant degree by the sound of the biophony, particularly as an acoustic guide or map. “Travel along this route as long as you hear the green ants sing, then, when their song ends, head toward another voice (and so on) till you get to the place you want to go.” The directions taken during their walkabouts are determined, at least in part, by changes in the soundscape.
The Jivaro, who live in the Amazon Basin and refer to themselves as Shuar, hear the language of the biophony very differently from the Pitjantjatjara. The soundscapes are dissimilar in the extreme: while the Pitjantjatjara desert landscape can be hauntingly still except for the most subtle signatures of wind, earth, and a very occasional creature, the Jivaro collective biome is one of the most acoustically rich environments on the planet and is never without creature sound at some level.
Once headhunters, the Jivaro fiercely resisted Westerners, from the conquistadores to twentieth-century missionaries. In 1599, after wiping out a Spanish town of around twenty thousand, they were considered to be so ferocious that they earned a reputation as the only South American tribe to effectively repel the Iberian invaders. They continued to rearrange the skull sizes of their adversaries until the late 1960s.
As with other tribes who live in remote locations, the Jivaro’s and Pitjantjatjara’s connections to natural soundscapes are quickly changing as contact with industrial culture becomes more frequent and imposing. But on my only visit, just before the Jivaro became more integrated into a cash economy, I was allowed to accompany a group of men on a rare evening hunt. I quickly discovered that they found their way through dense ground-level vegetation without the aid of torches or a clear view of the night sky, guided primarily by subtle changes in forest sounds. With startling accuracy, they were able to follow unseen animals, directed by the slightest variations of insect and frog articulation.
They also allowed me, an “outsider,” to experience their sacred songs and dances. With a couple of flutes and a type of rainstick, their music bore a strong relationship to the sounds around them and often appeared to be driven by the constantly shifting “moods” of the forest’s daytime or evening ambience. In one instance, the emotion of the music, in that attenuated moment before an afternoon thunderstorm, became quite somber and anticipatory. Then, prior to the evening chorus, after the squalls passed a short time later and the ambient forest sound picked up and became more lively, the performance resumed with a more upbeat theme and instrumentation. Echoing the mood of the environment, the tempo increased and the feeling was much more energetic. Whether the music was instrumental or vocal, or accompanying a dance, it drew deep inspiration from the signals emanating from the woods.
When I was trying to find a single, easy term that would define animal sounds coming from wild places, every expression seemed academic and obscure. In the human realm of noise, the terms were even more obtuse, with phrases such as anthropogenic noise. Nothing quite fit. Then, by accident, I hit on a Greek prefix and suffix that struck just the right chord: bio, which means “life,” and phon, which means “sound.” Biophony: the sounds of living organisms.
In addition to the sonic cues embedded within soundscapes, the biophony as a whole can give us valuable information about the health of a habitat. In an undisturbed natural environment, the richness and content of soundscapes vary from season to season, over time of day, and under different weather conditions. The organic and nonbiological elements that are unique to a location work in a delicate balance, acoustically defining each habitat, much in the way each one of us has his own voice, accent, and manner of speaking.
More than twenty years ago, I asked a biologist working for a large lumber company if I might have permission to record at a “forest management area” in the Sierra Nevada mountains, where his corporation had obtained a lease permit to begin selective logging on public forest land. The site: Lincoln Meadow at Yuba Pass, about three and a half hours east of San Francisco. Bisected by a stream and a bit over two-thirds of a mile long and about a quarter mile wide, the meadow was surrounded by ponderosa pine, lodgepole pine, red fir, white fir, and Douglas fir, as well as a few sequoias. Multiple species of frogs could be heard there throughout the spring. It was a lovely, resonant place. At local meetings held throughout the area, the biologist and his associates assured the community that his company’s new selective-logging methods—cutting only a few trees here and there and leaving the vast majority of the healthy old-growth sequoias standing—would have no adverse impact on the habitat. I asked for access to the site to record both before and after the operation.
With the company’s blessing, during the summer solstice of 1988 I set up my system in the meadow and recorded an exquisite dawn soundscape expressed by a wide variety of creature so
urces. Figure 1 is a graphic illustration of a twenty-two-second soundscape clip from that site. (A graduate student of mine once observed that the Lincoln Meadow spectrogram reminded her of an abstract painting of a forest.) Present in the first recording were Williamson’s sapsuckers (a type of woodpecker), mountain quail, chipping sparrows, white-crowned sparrows, Lincoln’s sparrows, ruby-crowned kinglets, and numerous insects. Note the density throughout the illustration.
Figure 1. Lincoln Meadow, 1988.
A year later, after the logging operation was complete, I returned to Lincoln Meadow on the same date, at the same time, and under the same weather conditions to record again. (The precipitation records during the winter of 1988 to 1989 had also been similar to those of the previous year.) When I arrived I was delighted to see that little seemed to have changed. However, from the moment I pushed the “record” button it was obvious that the once-sonorous voice of the meadow had vanished. Gone was the thriving density and diversity of birds. Gone, too, was the overall richness that had been present the year before. The only prominent sounds were the stream and the hammering of a Williamson’s sapsucker. I walked a few hundred feet back into the forest from the meadow’s edge, and it became quite apparent that the lumber company had wrought incredible devastation just beyond the meadow’s sight line, where extensive patches of ground had been left exposed. While not exactly a clear-cut, many more trees were taken than had been promised. In Figure 2, the stream is represented by the horizontal light-gray section across the bottom, and the woodpecker is the cause of the vertical lines in the center of the figure. Over the past two decades, I have returned more than a dozen times to the same spot at the same time of year, but the bioacoustic vitality I captured before logging has not yet returned.
Figure 2. Lincoln Meadow, 1989.
To the easily deceived human eye—or through the lens of a still or video camera—the site even now appears wild and unchanged from the narrow perspective of the meadow. With a photo, we can frame a shot in almost any setting and, depending on what we want to catch in that fraction of a second, evoke responses from awe to horror. Still photography lends itself beautifully to the close-up shots of single animals absent the complex communities they need in order to thrive, and is thus a kind of tolerated distortion.
But even a short, unedited sound recording captured in a calibrated and comprehensive way does not lie. Wild soundscapes are full of finely detailed information, and while a picture may indeed be worth a thousand words, a natural soundscape is worth a thousand pictures. Photos represent two-dimensional fractions of time—events limited to available light, shadow, and range of the lens. Soundscape recordings, if done right, are three-dimensional, with an impression of space and depth, and over time can reveal the smallest feature along with multilayered ongoing stories that visual media alone can never hope to capture. A well-tuned ear and attention to minutiae within the larger picture will always uncover any deception.
In marine environments, coral reefs tell much the same story as the meadow. A while ago, I went to Vanua Levu in Fiji to record living reefs that still produced and sheltered an abundance of organisms. In an unusual discovery, I happened to come across one that was stretched far enough—nearly a half mile in length—to contain both a living and dead component. When I dropped a hydrophone over the side of the boat to capture the part still vital, I was able to hear and record a spectacular variety of fish and crustaceans, including anemones, parrot fish, cardinalfish, clown fish, wrasses, puffer fish, fusiliers, goatfish, butterfly fish, and dozens of others. Figure 3 represents a ten-second clip of the dense, healthy reef habitat. (Of course, the actual sound tells the story more distinctly than any words.) In this illustration, the noise from the wave action at the surface can be seen below 1 kHz, while all the creatures are seen above.
Figure 3. Vanua Levu, Fiji. Live coral reef soundscape.
Figure 4 illustrates the soundscape of a nearly dead and badly stressed section of the same reef. You can still see the wave action below 1 kHz. But nearly all of the fish are gone, and only a few snapping shrimp remain as part of this marine biophony. Due to warming waters, shifting pH factors, and pollution, this sonic loss is occurring alongside the deaths of many coral reefs around the world.
Density and diversity are fundamental bioacoustic indicators when measured against season, weather, and time of day or night. If we can establish baseline recordings for any environments that are calibrated to known and repeatable standards—as I did at Lincoln Meadow and the coral reef in Fiji—then the recorded information we gather will represent a collection against which future recordings can be accurately assessed. I have always been careful to record with future comparisons in mind. When done properly, such recordings allow us to determine an expected acoustic dynamic range and to measure creature concentration and variety under an array of changing conditions. For example, we could ask ourselves: On a day with a clear dawn in late spring, just before sunrise in a remote, nearly pristine temperate forest habitat, what kind of soundscape could we reasonably expect to hear? If we record continuously over the course of a week’s time, and then over a few years to account for average rainfall, wind, and temperature—assuming that the flora and surrounding landscape have not been altered—we’ll get a pretty good idea.
Figure 4. Dying coral reef soundscape.
Whole-habitat recordings of the kinds I’ve described illustrate the state of biomes that have been rendered ecologically transformed through human intervention, such as logging or mining; climate change; or natural phenomena, and we can make efficient comparisons—assuming we have well-collected data sets—with audio snapshots as short as ten seconds in length. Like the rings on a tree, these recordings serve as multilevel biohistorical markers. When natural cycles, disasters, or destructive acts of human intercession occur, the events are quickly and powerfully articulated through changes in the biophony. The living collective of sonic organisms responds appropriately. Nonhuman animals will try to recalibrate their voices to accommodate the altered circumstances. The resulting spectrograms either will show far less density and diversity or will appear more chaotic—that is, filled with unrelated or competing information—with very little distinction between voices, assuming any remain at all.
The presence of water and food, the climate, the vegetation, the soil conditions, the season, and the altitude all affect the biophony. And all of these combined will help determine the cumulative number of creatures living in a given biome (its density) and the number of species present (its diversity). Then there are the geological features of the landscape, which will bring out specific qualities of a wide range of vocalizations, thus highlighting the unique character of the biophony—the way it actually sounds to the ear, human or nonhuman.
A rain forest is not just the tropical ideal most of us think of. There are many different types, and they reach from the tropics to the subarctic Pacific Coast regions of the Northern and Southern Hemispheres. The densely packed vegetation of broad-leaved, straight-trunked, and buttressed trees; bromeliads; epiphytes; saprophytes; orchids; figs; and carnivorous plants, along with numerous species of animals, make up the estimated thirty million or so flora and fauna that live in tropical regions with an annual rainfall of around 160 inches (about 400 cm). At the other extreme, in temperate or subarctic zones with annual precipitation of around 80 inches (about 200 cm), rain forests also exist, although the vegetation and animal life are much more sparse, even in the warmer seasons. While some animals, such as wolves, foxes, bears, and a few species of coastal birds, are year-round residents, most tend to migrate based on when and where food is most abundant. Populated mostly with spruce, cedar, hemlock, and Douglas fir, and an understory of ferns, berries, and nettles (in temperate regions), and with tundra (in northernmost zones), these rain forests are distinctly different from those nearer to the equator. The first thing I noticed about the disparity between equatorial and Southeast Alaskan rain forests is how dissimilar they sound. They’re b
oth “rain forests.” But the varieties of frogs and insects alone at the equator far exceed anything along the fifty-eighth parallel to the north. The organisms in equatorial rain forests tend to be year-round residents. Those farther to the north, in temperate zones, are seduced into song in the spring and summer months. They are more transient, or migratory, and vocalize seasonally. Meanwhile, the winter months are, in comparison, biophonically light.
Another extreme would be to compare a rain forest to a desert biome. The most noticeable difference is in the quality of the sounds. Rain forests tend to be reverberant habitats because of the high humidity and the moisture both on the ground and clinging to the vegetation. Desert biomes, by contrast, tend to absorb sound quickly because they lack moisture, and sound has nothing to “bounce” off of. While you might hear waterfalls and passing afternoon rainstorms in a rain forest, the geophonic sound signature of a desert is more likely to be wind and an occasional sand dune “singing,” although violent thunder and rain sometimes do occur. And there’s no comparison between the density and diversity of life in tropical rain forests versus deserts. Equatorial rain forests consist of the most densely populated biomes on the planet, while deserts and the Arctic regions—north and south—make up the least.
Tundra habitats are essentially treeless plains and are among the coldest of all habitats. Even though there’s plenty of water, precipitation is fairly light and the vegetation is sparse, consisting mostly of low-lying shrubs, short grasses, sedges, mosses, and liverworts, and a few hundred varieties of flowers spread across huge expanses. The density and diversity of animals tend to be light as well. The surface is soft, cushionlike, and a bit mushy. But underneath is a layer of permafrost—permanently frozen nonproductive soil. With the sound quality of the tundra similar to that of a desert, now and then perhaps you’ll hear the voice of an Arctic fox, maybe a wolf, voles, hares, a bear, Dall sheep, and squirrels. At certain times of year, mostly during migration, you’ll see caribou—thousands at a time, if you happen to be close to one of their routes, their snapping ankle tendons a characteristic sound signature, in addition to their cattlelike grunts. There are birds as well: depending on where you’re located, you’re likely to hear common and hoary redpolls, American robins, tree sparrows, white-crowned sparrows, Savannah sparrows, ptarmigan, ravens, sandpipers, lesser yellowlegs, warblers, terns, and wandering tattlers. Wildlife is dispersed over wide areas within very windy soundscape conditions. So, while the sonic fabric is robust overall, the bioacoustic texture is extremely delicate.
The Great Animal Orchestra Page 7