Having heard about my work in Africa, Michael “Nick” Nichols, a National Geographic photographer on a combined assignment from the magazine and the Aperture Foundation, reached out for additional media to accompany the images that would result from his trip. He was in Rwanda in 1987 to shoot one of the great ape families, mountain gorillas. For his second excursion to Karisoke—the late Dian Fossey’s aforementioned camp—Nick invited me to join him for a month to record the soundscapes of the Virungas and the biomes where the gorilla groups lived. These soundscapes, in turn, would become part of a traveling exhibition of his photographs, sponsored by Aperture.
During the trip I learned from Nick that none of the other sites where he had photographed had been recorded either. In order to get a complete picture of great ape habitats, I felt strongly that it was important to capture audio from those as well. I couldn’t get sufficient funding from institutional or corporate sponsorships, so I sold personal items, took out loans against my small San Francisco condo, and set out to record those sites, first at Gombe—Jane Goodall’s research camp on the northeastern shore of Lake Tanganyika in Tanzania—and later at Biruté Galdikis’s site, Camp Leakey, in Borneo.
The first thing I noticed at each location was how much emphasis the other researchers on-site—each concentrating on a narrow topic—placed on the visual aspects of their study animals. For those whose scope of work involved sound at any level, the biophony—and in many cases even the individual species’ sounds—was completely overlooked. Yet I realized quickly just how varied and rich the natural soundscapes were.
As my thesis gained traction, I no longer had to rely so heavily on my own resources and was frequently commissioned to go to various sites to collect sound for museum-exhibit installations. These adventures allowed me to further test and refine the concepts, bringing back more than just a collection of field recordings that would otherwise have limited purpose.
In Borneo—the third largest island in the world—a small riverboat took us the eighty or so kilometers from the Indonesian city of Pangkalanbuun to Camp Leakey on a slow two-day journey. Ruth Happel and I had just got off the boat and were walking on the trail from the dock to our cabin when we heard the call of an Argus pheasant. Not a second later I was looking down at the ground and found a huge feather from the same type of bird. The feather was one of the most beautiful I’d ever seen; the bird is called an Argus pheasant because its feathers have patterns that suggest eyes—the etymology refers to the giant Greek mythological character Argus, who had a hundred of them. Sometimes more than a yard in length, the feathers’ main shafts show off mesmerizing yellow-brown circular patterns. Highlighted in white, these “eyes” are framed by perfectly inscribed kohl linings, not unlike the eyes of our tabby cat, Seaweed.
It was midafternoon, and the forest was filled with the voices of insects, trogons, forktails, laughing thrushes, kingfishers, barbets, hornbills, mangrove pitas, green magpies, and so many other species that we quickly lost count. We had to get out there. Before signing in with the camp biologist and unpacking, we grabbed our gear and set out in a dugout canoe that we found by the dock to find a mangrove swamp we had passed on our way in. It was a delicate operation—we weren’t used to paddling dugouts with waterlines mere inches from the brackish river, and we were a bit nervous about protecting our equipment. But after about half a mile of cautious travel, we found the mangrove biome we were looking for—a perfect site, we thought. We tied the painter of the boat to an accessible branch and began to set up our gear.
It was now late afternoon, a couple of hours or so before dusk, and the forest was booming with sound. I pushed the “record” button. The first sound I noticed in my earphones consisted of maybe ten or twelve small splashes. I couldn’t tell what direction they were coming from because I was recording in stereo—but I did know that the noise came from something nearby. Then the soundscape shifted noticeably—insects became quiet, birdsong became lighter. A signal? We had been recording for not more than a few minutes, but when I looked over the side of our canoe into the dark, tannin-colored water, I could already see several three-to four-foot shapes swimming in circles close to the boat, although I couldn’t make out any detail and was unable to get an accurate count. Things were happening fast, and there was a feeling in the air that didn’t seem quite right. Then one that I didn’t see before broke the surface, and I heard Ruth, a woman of few words, mutter louder than usual, “Crocs!”
“I don’t think I like this,” I responded, trying desperately to sound calm. Pulling in our gear and cutting the painter, we made a quick run back to camp, never venturing out on the river again during our entire stay. When questioned by the staff, our excuse was that we found too many places to record on land—more than a half-truth, as it turned out. The gibbons of the region are the star soloists of the habitat.
It was just before dawn in a tower at the end of the Camp Leakey orangutan rehabilitation site’s dock. The lookout rises some fifty feet above the black-water Sekonyer River that flows by the site, just high enough that it aligns midway up the sumptuous canopy where gibbons and other primates in the area spend most of their lives. The gibbons of Indonesia are sunrise singers. Their songs are so beautiful that ancient Dayak myths speak of the sun rising in reply. In the remaining viable rain-forest habitats of Borneo and Sumatra, every dawn chorus is filled with the near-field and distant strains of long descending and ascending vocal lines as bonded gibbon pairs connect through elaborately developed vocal exchanges unique to each couple—alluring duets of affectionate concord.
The morning after our arrival, as we recorded the languorous glissando-like lines of the gibbon choruses, I was reminded of the many melodic and poignantly arranged operatic and folk vocal duets I had heard and performed over the years. When I returned home, I came across a short fourth-century Chinese poem that expressed exactly what I had been feeling:
Sad the calls of the gibbons at the three gorges of Pa-tung;
After three calls in the night, tears wet the [traveler’s] dress.
Unhappily, gibbons are now extinct in China. In Indonesia they, like several close subspecies, can still be found in dwindling numbers throughout the north part of Sumatra around Aceh Province—the location of the December 2004 tsunami—and in Borneo. Their duets can cover more than three and a half octaves, yet remarkably the gibbon voices become a perfect fit within the rest of the biophony.
Each discovery became a small revelation, but there were others. I finally realized that the biophonic behavior I was witnessing on paper probably wasn’t unique to Africa or Borneo. I found signs of temporal distinction in our own backyard. Northern Pacific tree frogs will vie for acoustic bandwidth, time-and frequency-wise: one frog will call, followed immediately by another at a higher pitch. Sometimes their calls overlap when they are fighting for sonic territory or when the result is (hopefully) an attractive mate. The three around our small lap pool have defined their respective territories—one at each opposite end, and one in the grass about midway between the other two. Even though their vocalizations are at slightly different frequencies and might be distinguishable as a chorus, they rarely overlap in time. Instead, they set up a neat, well-paced ¾-waltz-like rhythm, with the alpha frog setting the pace. No matter how fast the alpha frog croaks, the others fill the spaces in between in quick succession with their separate but distinctive croaks, no one masking another. When they really get rolling, it’s a fast 6/8; meter. I have no idea which frog got the desired companion, but one year the alpha frog was still croaking solo well into early June. Apparently still accommodating elegantly for competition, he performed measures with a single croak and rests on the other beats, where the other frogs, had they not disappeared by late May, would have fit in. And other examples of differentiated bandwidth were showing up everywhere in the numerous spectrograms I printed out, in recordings from Equatorial Africa, South Asia, and South America.
In older, healthy habitats, where the biophonic bandwid
th is well established and all the animals are more likely to vocalize together, each call is heard distinctly and each creature thrives as much through its voice as through any other aspect of its behavior. The connections of a particular species’ vocalization to survival and reproduction only become clear when we understand the function of an animal’s voice and its relationship to all others in its natural habitat. If an organism needs to be heard to successfully defend its territory or to communicate its viability to potential mates, then it requires clear acoustic bandwidth or noise-free time to do so. The same kinds of relationships occur in marine environments, such as flourishing coral reefs, where multiple species of fish and crustaceans thrive and generate acoustic signals.
Perhaps more surprising—yet in complete accord with this idea—is the fact that many animals communicate in an almost “underground” way that appears somewhat subtle to us; to them, it’s stealth. In 1990 a colleague and I had just finished three weeks of work at Jane Goodall’s earlier referenced chimpanzee research site, Gombe. We had a few extra days to wander about before our scheduled flight back to the States, and Goodall suggested that we check out a great hippo site in the Selous Game Reserve, along the Rufiji River in the middle of the country. Our camp, a typical African tourist and big-game-hunting facility, was located on the waterway, where we could see, from the high banks, large gatherings of hippos both on the shore and wallowing in the water below us. In an aluminum rowboat provided by the lodge, we drifted downriver with the current so that the river’s flow rate would equalize with the velocity of the boat and wouldn’t interfere with the hydrophone we had dropped over the side. As we passed submerged families of hippos, recorder rolling, it became immediately apparent that they vocalized underwater, their satiric, buffoonlike punctuated grunts revealing a fairly extensive and intricate vocabulary. As briefly mentioned earlier, hippos are social animals. In murky, crocodile-infested environments, this type of contact for animals with a highly developed social structure is germane to the safety of individual members and the bloat. When the family is submerged, members constantly vocalize to retain social contact with the others, mostly for protection since crocodiles share much of the same habitat.
Plains and forest elephants of Africa have found low-frequency transmission channels and a vocal syntax all their own. Over the wide-open grasslands and through the forests, their infrasound voicings are low enough—and their waveforms long and loud enough—that they can be detected at several kilometers distant throughout the territory, clearly signaling to others concepts such as “Join us” or “Let’s meet at such and such a location soon.” Likewise, wolves and coyotes, both extremely vocal animals, howl to remain in contact with other members of their respective families. Freshwater dolphins of the Ganges and Amazon, and places such as Lake Baikal in Russia—the world’s deepest lake—have evolved highly developed and successful echolocation processes that are specifically geared for the less dense and more murky waters they inhabit.
Mating and territory. Mating and territory. We’ve always been taught that the function of acoustic behavior by birds, amphibians, fish, and nonhuman mammals is about mating and territory. But hippos, elephants, cetaceans, and other animals clearly have extra motivations for vocalizing. In addition to using social vocalizations that enforce cohesion within groups throughout and across many species—especially mammals—some species have gone even further, evolving methods using sound itself as a tool. Many toothed whales, for example, send out bursts of sound that are sometimes referred to in marine bioacoustic jargon as the “big bang”—a highly focused eruptive beam that stuns their prey and slows it up enough so that the whales can snag their meal without expending too much energy in the process. In a clever adaptation, the snapping shrimp closes its large claw so fast that the speed forms a cavitation bubble, which bursts with an impact noise so loud that the sudden bang stuns the fish, giving the shrimp a quick, effortless snack.
The list of adaptive acoustic behaviors goes on. I have a recording, made in the fall of 1979, of a killer whale mimicking a barking sea lion, ostensibly to attract one through sound. The American dipper, mentioned earlier, is driven by ancient instincts to nest under waterfalls, yet its songs and calls pierce even the most raucous cascade. Meerkats, members of the mongoose family that live in Africa’s Kalahari Desert, fear sky-borne raptors more than almost any other type of predator. For protection, they’ve developed a specific alarm call that, when produced, immediately signals the other members to bolt for the cover of the nearest hole. Moths, mentioned earlier, have evolved to outsmart echolocating bats by jamming their signals. But in another adaptive solution, some bats, like Barbastella barbastellus, have managed to figure out what the moths are doing and have adjusted their echoing signal from a loud ping to a soft whisper. This allows them to creep up on their prey, drawing to within a wing’s length without being detected.
Whatever the objective of a signal—whether it’s mating, protecting territory, capturing food, group defense, play, or social contact—it must be audible and free from interference if it is to function successfully. Aldo Leopold almost got it right when he poetically described the call of a crane in A Sand County Almanac with these words: “When we hear his call we hear no mere bird. We hear the trumpet in the orchestra of evolution.”
What about that orchestra—the entire animal ensemble within which the crane is but one performer? In biomes rich with density and diversity of creature voices, organisms evolve to acoustically structure their signals in special relationships to one another—cooperative or competitive—much like an orchestral ensemble. That is, over time, unlike the vocalizations that occur at various stages of recovery in stressed or compromised habitats, natural selection has caused the animal voices that occur in many undisturbed regions to appear “organized.” The combined biological sounds in many habitats do not happen arbitrarily: each resident species acquires its own preferred sonic bandwidth—to blend or contrast—much in the way that violins, woodwinds, trumpets, and percussion instruments stake out acoustic territory in an orchestral arrangement.
The beautiful spectrogram in Figure 7, taken from a ten-second dawn chorus recorded in Borneo, clearly shows a complex biophony. It’s drawn from a habitat rich in vocal density and diversity. Look at this graphic from left to right as if you’re reading an extended bar of music. Birds, insects, and mammals each form their own temporal, frequency, and spatial niches. (Note that the cicada fills three slots at the same time—a remarkable feat that must have taken a long time to evolve successfully.)
Figure 7.
Where disparate groups of animals have evolved together over a long period, their voices tend to split into a series of unoccupied channels. So, each sonic frequency and temporal niche is acoustically defined by a type of vocal organism: insects tend to occupy very specific bands of the spectrum, while different birds, mammals, amphibians, and reptiles occupy various other bands, where there are fewer chances of frequency or temporal overlap and masking. Animal voices in many habitats have evolved so that they can stay off the acoustic turf of others. When that partitioning occurs, individual voices can be clearly differentiated from one another, and the benefits of their vocal behavior are maximized. And when there is occasional conflict, the acoustic territorial disputes are sometimes solved by timing: first one bird, insect, or frog might sing, then others when that one quits.
It turned out that nearly every tropical and subtropical habitat I had captured on tape was made up of a variety of partitioned voices that formed collective sound signatures, each of which uniquely defined a place and time and served as a unique voice print—a territorial sound-mark. I had made thousands of recordings before my Kenya trip, and subsequent travel to many wild sites over time added weight to my thesis, which, by the late 1980s, I had renamed the niche hypothesis—thanks in large part to the inspiration of Ruth Happel, who was still a graduate student at Harvard studying primatology during our trip to Borneo. Ruth quickly drilled down to the
essential questions that were necessary to uncover the mysteries of wild voices. While floating down the river heading home from Camp Leakey in 1991, she asked out of nowhere, “How do all these animals hear each other if they’re all vocalizing at the same time?” From that sensibility she arrived at a hypothesis that defined collective vocal behavior as possibly more germane to survival than were single voices. With a rare ability to think like the organisms in the animal world she studied, Ruth understood intuitively, without knowing at the time exactly what the operational mechanism was, that nonhuman animal voices must have evolved so that each can be heard unmasked and without interference. Her insight gave me a new theoretical map to work from.
The radius within which a frog, bird, or mammal voice can be heard is a mark of many complex factors. Food and the availability of mates have significant influence over where creatures live, but we also know that the geological and botanical features of the landscape, combined with time of day, weather, and climate, play important roles as well. We know that higher voices tend to travel shorter distances—because the wavelength is shorter, and it takes more energy to project a shorter sound wave—and lower voices travel farther. What, then, might be the additional acoustic factors that would cause a creature to choose one location in which to live over another?
The Great Animal Orchestra Page 9