CHAPTER EIGHT
Noise and Biophony/
Oil and Water
It was a spring day at Mono Lake, California, a body of water located east of Yosemite in the Eastern Sierras and formed over 750,000 years ago. Because it lacks an outlet to the ocean, the water over time has become quite alkaline and salty—about two to three times the saline content of the sea. Ken Norris, then head of the Environmental Studies Department at the University of California, Santa Cruz, wasn’t much interested in the lake. He wanted to know if there were any vocal organisms in the vernal pools that surround this stunning spot. An early supporter of the niche hypothesis, Norris encouraged me to take a hydrophone and have a listen. “I’ve got a hunch,” he assured me.
A few hundred yards south of the road that cuts west to east tangent to the lake’s north side off Highway 395, I found a shallow depression filled with about six inches of newly melted snow and ice. It was late March, and the weather was crisp, clear, and warm during the day—though still freezing at night. At first there was no wind and, except for a few California gulls, no other sound. Because the sandy and porous environment soaks up acoustic reflection, the High Desert tends to feel relatively quiet. But there is a sound that stands out. Great Basin spadefoot toads begin their synchronous performances around midafternoon, as the area falls under the shadow of the high mountains to the west, carefully injecting each iteration of their aggregated voices into the airspace around the edges of the water-filled depression.
I uncoiled the cable and carefully lowered the hydrophone into the pool, put on my earphones, and switched on the tape recorder—a well-established ritual sequence. Caught completely off guard, I heard my headset explode with a variety of small crunching sounds, high-pitched squeaks, pops, and scrapes—each one, I assumed, biological. After recording for a while, I took a small bucket and shovel I had brought along just in case and, sifting through the muddy water, discovered water boatmen, insect larvae, and tadpoles, each adding a face to the marine voices I had just captured. Eventually I plugged a microphone into one channel and a hydrophone into the other. With the hydrophone under the surface and the mic above water, I tried to see if the spadefoot toads transmitted their vocalizations simultaneously in and out of the marine habitat so vital to their existence. They do. It was an exhilarating experience to encounter this and to be one of the first to actually hear it. Norris’s instincts were right again.
Great Basin spadefoot toads are wondrous critters. Once, when I was working as a field associate at the California Academy of Sciences, I walked into the renowned ornithologist Luis Baptista’s lab for a meeting. I was early. “See this?” he asked excitedly, without a proper greeting. He pointed to a glass jar containing an object that looked like a small-size dolma—the Greek dish also known as stuffed grape leaves. “It’s a carapace with a toad inside. It’s been sitting on my desk for five years without any food or water, and it’s still alive.”
“How is that possible?” I asked skeptically. “I didn’t know you were into toads.” Ignoring my comment—Baptista was into everything—he rose from his desk, picked up the jar, and walked with a quick, jaunty gait to the sink. He filled the bottom of the jar with about a quarter inch of water—just enough to partially dampen the carapace—and set it on the table. After our meeting we went to lunch. When we returned to the lab in a few hours, a spadefoot toad had emerged—alive—after five years in a jar.
When conditions are optimal, and the winter precipitation that has accumulated on the desert surface melts and moisture reaches the toads—which are buried under three feet of hardpan desert soil—they emerge with their spadelike feet from their wrappings and dig to the surface to breed, lay eggs, and mature. At the completion of their cycle, they burrow down a meter or so into the difficult terrain, where they remain encased in an almost impermeable membrane—sometimes for years—before surfacing to endure their brief breeding phase once again. (A spadefoot toad will have a life span of roughly eleven to thirteen years in the wild.) When they finally do appear, they congregate around the vernal ponds described earlier—to vocalize in well-calibrated choruses.
Historically, spadefoot-toad vocalizations have been thought to serve two main functions: attracting a mate and protecting territory. But we may have overlooked another important explanation that is tied to their survival: a synchronous chorus assuring a seamless protective acoustic texture. With synchronicity, when all the toads are vocalizing together, acoustically oriented predators such as foxes, coyotes, and owls must struggle to draw a bead on any one, because no individual becomes conspicuous. If the pulsating, rhythmic structure is lost, however, and individuals become noticeable when trying to recoup their place in the chorus, all hell can break loose. Avian raptor and canid opportunists are forever on call for such moments.
Chorusing is a function that can serve, among others, to thwart predation. Within the limited world of the species itself, the toads hear each voice as distinct. The vocal characteristics of spadefoot individuals are so unique that when heard by others in the resident group, they are able to compete for mates quite aggressively while at the same time protecting the integrity and survival of the group by lending their voices to the choir. Given our limited abilities to make fine acoustic distinctions, however, we’re not easily able to hear the differences between individuals. Acting collectively, each vocal member within the crowd enjoys a degree of anonymity and protection.
Figure 10 demonstrates spadefoot-toad chorusing without any breaks in the sequence and no disruption from human-generated noise. It is a powerful story told through the aggregate voice of dozens of chorusing frogs in about ten seconds—the length of the audio clip from which this spectrogram was made.
Figure 10. Synchronous Great Basin spadefoot toads (Spea intermontana) chorusing.
Figure 11 illustrates the story line’s denouement. In this ten-second clip, we see what happens when a military jet flies low over the terrain nearly four miles west of the site, its booming noise—measured at approximately 110 dBA at our monitoring location—masking the toad vocalizations. Most of the aircraft signature can be seen at the bottom of the page under 1 kHz. Note the breaks in the chorusing and how the toad group energy diminishes. Far less robust than the chorus in Figure 10, these “breaks” set up a momentary opportunity for predation to occur. In this instance, it took some time for the toads to reestablish their protective acoustic connection—from thirty to forty-five minutes after the noise faded—and under a bright moonlit sky, my wife and I watched from our nearby campsite as a pair of coyotes and a great horned owl swept in to pick off a few toads during their attempts to reestablish vocal synchronicity.
Figure 11. Spadefoot toad chorusing affected by military-jet overflight.
It’s not just the sounds of a single species—those related to mating, territory, communication, or protection from predation—that are affected by noise. Human-generated noise affects entire biophonies. Midmorning, while I was recording in the Amazon in the early 1990s, a multiengine plane flew at two or three thousand feet directly over our research site. The engine roar was so loud that it completely masked the chorus of birds and insects. When we looked at the effect of the noise on the soundscape, we found that the interference caused many creatures to stop vocalizing and others to significantly alter their patterns. The momentary break in the integrity of the biophony left open the possibility that many creatures would become victims to opportunistic predators, such as hawks or resident mammals. Animal vocal behavior that morning had been critically disturbed just long enough for such events to occur.
Figure 12 represents a twelve-second sound clip illustrating the normal biophony of the diurnal transition between dawn and midmorning choruses. Notice the delicate biophonic patterns of insects, frogs, and birds. Figure 13, also twelve seconds, is taken from about two minutes later as part of the same recording sequence. It shows how the biophony broke up because of the plane flying overhead, its integrity shattered by the engine
noise. It took a little more than five minutes for the jet noise to completely disappear—a result of the plane flying so low. If it had been at a higher altitude, the noise would likely have resonated for several minutes longer.
As in the Amazon, the effects of noise on the biophonies of the Sierra Nevada mountain range are beginning to be recognized. In the early 2000s, I, along with Stuart Gage from Michigan State University and a few other colleagues, received a commission to do a yearlong initial soundscape study in Sequoia and King’s Canyon National Park—a large but not-as-well-known park as Yosemite and a few miles to its south. Our objective was to establish a baseline collection of soundscapes from four sites over each of the four seasons. During our third session, in late May, we had just set up our mic systems to measure the dynamics of a spring dawn chorus when a formation of F-18 military jets from the nearby Lemoore Naval Air Station flew overhead. Even though they were flying more than two miles above us, the low-frequency rumble at one end of the spectrum, combined with the high-speed screams of the aircraft hurtling by, caused the biophony to suddenly drop off. After the jet noise disappeared some six or seven minutes later, the area remained quiet—the dawn chorus not rebounding to the peak levels that we recorded when there was no aircraft noise.
Figure 12. Amazon dawn-to-midmorning transitional biophony.
Figure 13. Same site as Figure 12 two minutes later, during multiengine jet flyover.
David Graber, the chief scientist of the Pacific West Region of the National Park Service stationed at Sequoia and King’s Canyon National Park, remarked to us that the mix of species, as well as the total number of birds, had been declining over the nearly two decades that he had been present. Since for several years the park had been affected by severe air pollution coming from the Central Valley to the north, by a period of drought, by a measurably warmer climate, and by a noticeable increase in noise from motor vehicles of all kinds and jet aircraft outbound to the east from the air base in nearby Visalia, he wasn’t sure what combination of factors was causing observable changes in bird-species numbers and population declines overall. And while initially there was a decline in toad and frog populations, some of the species’ numbers had appeared to stabilize. Having noticed the noise issue, Graber encouraged our study because it addressed, as a factor of our proposal, noise as a specific problem that could be examined in order to recommend improved policy guidelines.
During our Sequoia research program, we implemented new techniques and acoustic models with which we hoped to measure a wide range of conditions that affect the natural soundscape. These included all of Graber’s concerns plus the issue of the habitat’s landscape and biotic features (we were simultaneously working at four different types of sites within the park: oak forest, edge chaparral, riparian, and alpine). During these sessions, we began to confirm the loss that many of us had instinctively been feeling for some time. At every site I had recorded in the western United States and where I had returned over time to record again, patterns were beginning to emerge, such as shifts in the number of bird species and the density of their total numbers, as our work in Jackson Hole showed. Early indications from the data collected at Sequoia revealed that even distant noise-producing mechanisms interrupted the dawn chorus of many biomes within earshot—all at the same moment, many with cumulative impact. And although a lack of automated monitoring stations kept us from positively confirming this observation at the time, a shift in the biophonic mix of one site even appeared to have a similar bioacoustic effect on others nearby.
Little by little, data from the long-term audio collections we’re building points to a noticeable overall decrease in creature density, diversity, and richness across many species in many environments, including some in Africa, Alaska, the Amazon Basin, Costa Rica, and the American West. However, we have yet to fully understand the operational mechanisms that determine the rates of recovery from noise intrusion (if the biophonies actually recover at all). As mentioned earlier, sometimes—if the biome is physically uncompromised and only intermittent anthrophony is an issue—revival of the natural soundscape from the effects of an event can take just minutes. On the other hand, depending on the relative impact of human intervention to the habitat, recovery can take much longer—nearly an hour, or a day, or even years. As many naturalists have observed, several species of birds, such as starlings, hawks, crows, sparrows, and robins, and some mammals, such as coyotes and even an occasional mountain lion, living in and around noisy urban environments seem to have habituated somewhat to the clatter we generate. There is no precise data on just how they have managed to acoustically accommodate to these surroundings. But, as their once-wild habitats are decreasing, mounting numbers of wild creatures have been observed finding new sites very close to or within range of human dwellings.
Noise wasn’t much of a factor when I first ventured into the field in the 1960s. We were limited by the amount of time we could record with analog systems, so we needed to be selective. But even with so much to lug around and so little active recording time possible on-site, we didn’t need to work so hard to find ideal spots—many were still viable—and the small sample sizes of our recordings made it less likely that we’d hear an interruption.
When much lighter and more portable digital audiotape (DAT) recorders came on the market in the late 1980s, granting us longer recording times, we began to capture more noise, partly because there was more noise but also because of the extended recording times themselves. It was becoming a noticeable and serious problem because it obscured the protomusical structures that made the biophonies particularly lovely to hear. Digital audio software for handling recorded sound was improving with each passing week, making it easier to handle and archive larger quantities of field recordings, so when we did manage to get clearly stated natural soundscapes, the recordings were more robust than ever.
Now, with solar-powered digital technologies containing no moving parts (only flash memory cards), not only are we tapeless but we no longer need to rely exclusively on hard drives on which to store data. We can place numerous recorders at given sites and record for hundreds of hours at a stretch with each unit—some packages weighing no more than a couple of pounds and providing quality recordings that well exceed those made just fifteen years ago with the best and most expensive gear. We hear it all: the good, and the bad.
The roots of our musical history can still be heard in the murmurs and sighs of a few remaining old-growth forests. At some very remote sites, the organized voices probably have shifted only moderately during the blip of geological time over which humans have existed. Yet the wealth of sonic information hidden within them is becoming more difficult to hear, because the biophonies are often masked. The impact of noise on my work has increased exponentially: taking into account the effect of habitat loss due to land development or resource extraction, I’m sorry to say that to record one noise-free hour of material now takes more than two hundred times as long as it did when I first began more than four decades ago. As the truly wild sites become fewer in number, the likely result is that human habitation or industry will always be close enough within range that anthrophony will almost never be completely absent. Based on many years of field experience and how much uninterrupted natural sound in a wild habitat I’m able to record in an hour, I’ll make an educated guess that anthrophony can be heard in more than 80 to 90 percent of those biomes much of the time.
While noise diminishes our own experiences of the wild, creature behavior itself is likewise altered as a result of noise-induced stress. We know from observing wild animals held in captivity that they are greatly affected by their urban soundscape environments. (Captivity itself, of course, introduces its own behavioral stress issues.) In 1993, for example, a military jet buzzed Sweden’s Frösö Zoo—about three hundred miles north of Stockholm—during a routine training flight. The tigers, lynx, and foxes panicked. The animals tore apart and ate twenty-three of their babies altogether, including five rare Siberian tiger cu
bs. Trying to protect their offspring from the onslaught of noise, the panicked animals resorted to infanticide.
Scott Creel, a professor at Montana State University, published a now-famous study on the effects of snowmobile noise on wolves and elk in Yellowstone, Isle Royale, and Voyageurs National Parks in 2002. Creel and colleagues measured the glucocorticoid enzyme levels in the feces of wolves and elk, which gave the researchers an indicator of the animals’ stress responses. The secretion of glucocorticoids is a classic endocrine response to stress, and any measured increase in the levels found in many mammals correlates to escalated hypertension. The study concluded that the enzyme level found in the feces of both groups rose in direct proportion to the level of noise. When snowmobile noise was not present, the stress enzyme levels dropped back to normal. While it was clear that the noise induced stress, the authors also concluded that noise hadn’t yet had an effect on the population dynamics of either group. (The study, incidentally, was partly funded by the timber industry in Michigan.)
When noise is introduced into a soundscape, disrupting the normal acoustic dynamics of a biome, animals tend to exhibit restless behavior. One of the first signs is that they either become silent or, depending on the noise, express fear through alarm calls.
Some animals are more obviously affected than others. In a spectrogram, the dropout of a number of insects often occurs. If the noise is intrusive and has a wide enough bandwidth, it will mask the voices of frogs and birds as well as mammals, and they, too, will stop vocalizing. In a rain forest, raptors, large wild cats, and other predators that rely on subtle changes in the soundscape need to adjust their behavior since it is more difficult for predators to hear their prey, and for prey, in turn, to hear the slight danger signs of potential attack. Noise in marine environments will cause fish to exhibit group aversion behavior, as many of us have witnessed when we tap the glass on the side of a large tank filled with several of the same schooling species. Simultaneously and instantly the school will veer in the opposite direction from the impulse noise. Noise may also weaken immune systems in mammals and fish—as is potentially the case with the elk and wolves exposed to snowmobile noise—and in the process compromise resistance to disease, the natural physiological result of high-stress hormone levels. And where the noise signal is loud enough, it may cause physical damage or death.
The Great Animal Orchestra Page 17