SCIENCE AND CULTURE

Artists and scientists come together to explore themeaning of natural soundAmy McDermott, Science Writer

David Monacchi has spent the last 20 years hiking intosome of the most remote habitats on Earth. He’s ca-noed through flooded Amazonian forests and treaddeep into the jungles of Southeast Asia and Africa.But he isn’t on a quest for rare animals or for samplesof their remains. Monacchi, a composer, is hunting forthe ecosystem’s sound.

Sound is everywhere in tropical forests. Rain dripsfrom water-slicked leaves, birds screech, monkeystitter and bellow, branches crack, wind moans, andinsects chirp and buzz. Vibrations pierce the humidunderstory and echo through the airy canopy, creat-ing a symphony of sounds that speaks to both artistand scientist.

Monacchi is harvesting artistic inspiration as well asdata. The chirps and rattles contain information about

how species interact with the environment and eachother, as well as the health of the habitat. SometimesMonacchi uses his recordings to inspire the public,sometimes to inform ecological research. “I’m tryingto be at the edge of both worlds,” he says.

People straddling music and science often have avariety of titles. Monacchi usually describes himself asan interdisciplinary artist. Sometimes he prefers soundengineer or ecoacoustic composer.

Likewise, names for this field vary. For ecologists,the study of sound’s role in ecological processes is ecoa-coustics (1). For composers, it’s soundscape ecology oracoustic ecology. Labels fall away as creative specialistsin the arts, the natural sciences, or both come togetherto collaborate. They work with environmental sound fora variety of reasons—sometimes musical, sometimes

In February 2016, DavidMonacchi sets up the three-dimensional recording systems for the circadian 24-hour continuousrecording in terra firme primary forest habitat in the Tiputini River area, Yasunì National Park near Coca, Ecuador. Imagecredit: Alex d’Emilia (photographer).

Published under the PNAS license.This article contains supporting information online at www.pnas.org/lookup/suppl/doi:10.1073/pnas.1908588116/-/DCSupplemental.

12580–12583 | PNAS | June 25, 2019 | vol. 116 | no. 26 www.pnas.org/cgi/doi/10.1073/pnas.1908588116

SCIE

NCE

AND

CULTURE

Dow

nloa

ded

by g

uest

on

Dec

embe

r 18

, 202

1

scientific, and sometimes both. All strive to understandand explore the environment using sound.

Sound ScienceMonacchi first hatched the idea for his project, Frag-ments of Extinction, in 1998, a few years after biologistE. O. Wilson estimated some 30,000 species disap-pear every year (2), numbers rivaling the five massextinctions of the geologic past. Horrified by thescope of loss, Monacchi set out to collect sound por-traits of primary equatorial forests and capture theaural complexity of these last undisturbed environ-ments. His ultimate goal is to play them for the publicin art and science museums, inspiring reflection on allthe species that could disappear. The recordings arealso a reference for future generations, he says, to beable to look back on these ecosystems, if and whenthey are damaged.

It’s not easy to capture the sonic complexity of aforest. Sound comes from near and far, from aboveand below. Record a forest on the dual audio channelsof a smartphone, for example, and the playback from itssingle speaker will seem to emanate from a singlepoint. To reconstruct realistic wild habitats, with soundscoming from all directions, Monacchi records 24-hoursound portraits of virgin forests, using state-of-the-arttechnology with numerous microphones and channels(Audio S1 and S2*).

He plays his recordings for the public in speciallybuilt theaters in Denmark and Italy, which are studded

with up to 43 custom-built high-definition speakers onthe walls, floor, and ceiling to recreate the sphere ofsound around a listener. “We are taking samples ofthis fantastic heritage,” Monacchi says, “and we arebringing them back to the people of museums, inorder to reflect on the beauty, the fragility, the com-plexity, the balance of these habitats.”

To study the Fragments of Extinction recordings,Monacchi partnered with naturalist Almo Farina, anecoacoustics pioneer based at The University ofUrbino in Italy. One central tenet of the field, Farinaexplains, is that animals hear and recognize certainsounds, interpret them, and change their behavioraccordingly. An environment’s acoustic complexity,quantified as the number of sound events in a re-cording, offers a glimpse of the many signals that or-ganisms use to navigate their surroundings, selectsuitable habitats, and track resources.

Identifying acoustic events in a sound file can helpecologists parse the interplay of animal vocalizationswith other natural and man-made sounds, such as aburbling creek or a gunshot (3). It may also offer insightinto the health of the environment, at scales from indi-vidual species to communities (4). For example, twoyears after a devastating 2011 wildfire ripped throughsoutheastern Arizona’s sky islands—isolated mountainsrising from the intersection of the Sonoran andChihuahuanDeserts—insect communities remained relatively quiet.Their sounds were only audible in recordings from 18%of burned sites, compared to 55% from non-burnedlocations, offering land managers valuable insight intothe ecosystem’s recovery after the burn (5).

Musician Matthew Burtner makes field recordings of Alaska’s Matanuska Glacier in June 2014 as part of a sound cast(Audio S3). Image credit: Matthew Burtner.

*Audio credit: David Monacchi.

McDermott PNAS | June 25, 2019 | vol. 116 | no. 26 | 12581

Dow

nloa

ded

by g

uest

on

Dec

embe

r 18

, 202

1

A major challenge for the young field of ecoacous-tics is standardizing methods to identify and countacoustic events. Farina published an approach in 2016that scans audio files for sound’s complexity andevenness. He now wanted to apply his method, calledEEDI, to two of Monacchi’s 24-hour recordings fromraucous, undisturbed forests in Borneo and Ecuador,likely two of the most acoustically rich habitats on theplanet, Farina says. He expected their sound com-plexity to behave something like a fractal, with greaterintricacy at finer scales.

To test this prediction, Farina used EEDI to breakeach sound file into six-minute chunks, which he an-alyzed for audio events. Then he repeated the processat 10 finer timescales, down to one second. His resultsmatched his prediction. “The more fine-grain thescale, the more codes you find,” Farina says. “It’s notthe presence of individual codes that’s important, butthe behavior of codes across a sequence of scales.”Validating the EEDI methodology is a step towardstandardized analyses in ecoacoustics, Farina says,which can help ecologists judge habitat quality andlandscape change.

Cases such as this illustrate the power of sound asscientific data, but it does have limitations Farina says.For one, not all species vocalize or rely on their hear-ing. Some lean on other senses, such as sight, touch,and smell, to interpret their environment. Methods tocollect acoustic data are also far from standardized, hesays, and metrics to extract information from audiofiles are also limited.

Even so, sound naturally fosters interdisciplinaryefforts such as Farina’s and Monacchi’s by drawingartists to scientists who know the latest analyticaltechniques, says soundscape ecologist Bernie Krause.The medium, Farina adds, also draws scientists toartists, who often have better audio equipmentand better-honed communication skills. “Our aim isthe same,” he says, “to collect information to informpeople.”

Sound InspirationArtists often strive to recreate soundscapes: to bringthe experience of a rainforest or thundering oceaninto a concert hall, radio performance, or exhibitionspace. Evoking an artistic sense of faraway landssometimes involves warping and manipulating re-cordings and playing them in combination with theoriginal sound files.

Composer HildegardWesterkamp’s piece Beneaththe Forest Floor carries listeners into the extreme quietof Vancouver Island’s old-growth forests. It beginswith a low thumping sound—a recording of a raven’scall, slowed down. Westerkamp captured it and many

other sounds on Vancouver Island in British Columbia,Canada, then wove them together in a digital studio inToronto. When Westerkamp first heard the raven, shewasn’t sure how it would feature in her creative process,but “when I slowed it down, it sounded like drumbeats.It became an instrument,” she says. This audio trickechoed the traditional mythology of West Coast cul-tures, in which the raven is a symbol of mischief.

Westerkamp also sought to share both the stillnessand majesty of the forest’s towering trees. “Not onlydid I want to evoke the feeling of being there,” shesays. “But more importantly I hoped that it wouldmotivate listeners to go to these environments andexperience them first-hand.”

Director Gus Van Sant heard something more inWesterkamp’s recordings. He used an excerpt of thesong in his 2003 film Elephant—which was inspired bythe tragic 1999 school shooting in Columbine, CO—

to punctuate the chilling moment when the shootingbegins. “He made me aware in hindsight of how darkmy piece actually is, of the fearfulness and mystery ofthe forest,” Westerkamp says. “It highlighted for meonce again, how differently we all listen.”

Sometimes evoking an environment means com-bining sounds in unexpected ways. Ecoacoustic soundartist Matthew Burtner makes sonic portraits of gla-ciers, which he calls sound casts, using field recordingsto represent the whole geologic feature in a singlepiece (Audio S3†). Glaciers are impressive sights, butimages don’t capture the slow-motion grinding, livingquality of these dynamic rivers of ice, Burtner says.Through their cracks, booms, trickles, and bellows, hehears glaciers come alive.

To make his glacier sound casts, Burtner installs avariety ofmicrophones and hydrophones over a glacier.Some sit on its snowy surface, others hang down intocrevasses, and still others rest in trickling meltwaterstreams. He uses rough-and-tumble microphones typ-ical of geology research to pick up sounds in mud pitsand other low-gurgling, crunching places and hydro-phones suited for marine mammal research to catchhigh frequencies.

Back in his studio, Burtner pipes his recordingsthrough an array of speakers spread around theroom. He, like Monacchi, aims to capture the three-dimensionality of sound. Burtner arranges the speak-ers so that a listener in a gallery or concert hall would“hear a crack of ice on your right and then hear ittraverse the glacier and be on your left a millisecondlater,” he says. “You can hear the dynamics of theglacier unfolding.”

What emerges is an impression that even a moun-taineer couldn’t experience in person. Booms andechoes of the entire glacier, recorded from its craggypeaks down into icy cracks where no hiker could go,surround the listener simultaneously.

“You can hear the dynamics of the glacierunfolding.”

—Matthew Burtner

†Audio credit: Matthew Burtner, from “Sound Cast of MatanuskaGlacier” and “Threnody (Sikuigvik)” (BMI) from the albumGlacierMusic (Parma).

12582 | www.pnas.org/cgi/doi/10.1073/pnas.1908588116 McDermott

Dow

nloa

ded

by g

uest

on

Dec

embe

r 18

, 202

1

Sonic CollaborationOften, artistic and scientific sound projects aren’t sodifferent. Recording and editing sound files, whetheranimal calls or the pops and thumps of a glacier, re-quire a complex knowledge of instrumentation andsoftware, Monacchi says. “For us, dealing with sciencewas never that far away.”

That was certainly the case for soundscape ecolo-gist Krause. Working as a professional studio musicianin the 1960s and 1970s, Krause played for pop artistsGeorge Harrison, VanMorrison, and TheDoors. Then in1970, he and Paul Beaver released the album In a WildSanctuary, which incorporated natural soundscapes.Thus began Krause’s journey to investigating naturalsounds. He made high-quality recordings of whole hab-itats in his free time, intrigued by their acoustic structure.

After finishing his doctorate in creative sound artsin 1981, with a focus on bioacoustics, Krause devel-oped his niche hypothesis: in healthy habitats, differentspecies vocalize in unique bandwidths, each occupyingtheir own acoustic territory (6). Krause found that theseterritorial boundaries tend to disappear in stressedenvironments. The collective sound of the habitatbecomes chaotic as the organisms still present viefor acoustic territory, searching for new, availablefrequencies or new times to hoot and titter.

At Sugarloaf Ridge State Park in Sonoma County,near Krause’s longtime home in Northern California,he documented an encroaching quiet, coinciding withthe state’s prolonged drought. Krause has been re-cording every spring at Sugarloaf Ridge since 1993,and he documented the sounds of birds, insects, andother life dropping progressively from 2011, with asharp drop in vocalizations in 2015.

Krause published the findings in an article, coauthoredwith Farina, on sound as a way to study climatechange impacts in 2016 (7). He and Farina are nowworking on a second collaboration, with ecologistJerome Sueur of the National Museum of NaturalHistory in Paris. Since California’s historic 16-yeardrought ended in 2017, Krause is hopeful for theSugarloaf site. Heavy spring rains have called it backto sonic life, he says.

Ecologists and artists converge around acousticsbecause they know sound reveals otherwise-hiddendramas about both the natural world and humans’relationship to it. Working together, colleaguesacross disciplines can “use the power of science tounderstand phenomena,” Monacchi says. “And usethe power of art to share phenomena with the broadpublic.”

1 J. Sueur, A. Farina, Ecoacoustics: The ecological investigation and interpretation of environmental sound. Biosemiotics 8, 493–502(2015).

2 E. O. Wilson, The Diversity of Life (Harvard University Press, Cambridge, 1993).3 A. Farina, S. H. Gage, Ecoacoustics: The Ecological Role of Sounds (Wiley, Hoboken, 2017).4 A. Farina, N. Pieretti, P. Salutari, E. Tognari, A. Lombardi, The application of the acoustic complexity indices (ACI) to ecoacoustic eventdetection and identification (EEDI) modeling. Biosemiotics 9, 227–246 (2016).

5 A. Gasc et al., Soundscapes reveal disturbance impacts: Biophonic response to wildfire in the Sonoran Desert Sky Islands. Landsc. Ecol.33, 1399–1415 (2018).

6 B. L. Krause Bioacoustics, habitat ambience in ecological balance. Whole Earth Rev. 57 (1987).7 B. Krause, A. Farina, Using ecoacoustic methods to survey the impacts of climate change on biodiversity. Biol. Conserv. 195, 245–254 (2016).

McDermott PNAS | June 25, 2019 | vol. 116 | no. 26 | 12583

Dow

nloa

ded

by g

uest

on

Dec

embe

r 18

, 202

1