Case Study

The Elephant Listening Project

BIOACOUSTIC MONITORING portends a sweeping change in our ability to listen in on the cacophony of the wild world—and perhaps even make sense of it.

Onthe edge of this forest clearing in the Central African Republic, halfa dozen researchers and Ba’Aka assistants perch on an elevated platform,sweating, swatting flies, and gazing through binoculars at the forest elephantsbelow.

Ordinarily, this species of elephant(Loxodonta cyclotis) stays hidden beneath the forest canopy. Theirtrumpets and rumbles are occasionally heard, but the elephants themselvesare rarely seen—except in rare clearings like this one. They come hereto dig pits in the sand and drink the briny water that lies below.

At present, 100-odd elephants aremilling about, cavorting, scoping out mates, or digging for minerals. Butthe researchers’ attention is focused on a single mineral pit where a stout-tusked male named Eli stands, sucking brine into his trunk. Greyboy, a smallermale, lumbers toward the same pit.

And then it happens—Eli lunges outof the pit and rushes at Greyboy. Just before the two freight trains collide,Greyboy turns and runs, shrieking. Eli returns to his pit, rumbling deeply.He is answered by two higher-pitched rumbles coming from other elephants.

These rumbles and shrieks are recordedby a network of eight acoustic monitoring devices placed around the clearing.But it’s no simple tape-recording. The network is so finely tuned thatit uses millisecond differences between the times when sounds arrive atdifferent sensors to pinpoint the specific elephant—out of 100 animals—thatgave a particular call.

Welcome to the world of bioacousticmonitoring, where the cacophony of wild beasts and the quiet toil of conservationmerge into one.

It may sound technophile, but the data collected by this gadgetry will apply directly to an important conservation problem: using the calls of these elephantsto estimate the size and structure of their otherwise-invisible populationand to monitor changes that might portend poaching.

Bioacoustic monitoring is an obviousfit for describing populations that inhabit dense forests, underwater habitats,or other niches where visual observation is difficult or impossible. It’salso ideal for species that are sensitive to disturbance, since you canmonitor for months without visiting the site. And acoustic monitoring isless labor-intensive than many other animal-counting methods.

But the potential power of the techniquegoes far beyond that, says Katy Payne, the researcher with the CornellUniversity Bioacoustics Research Program who is spearheading

the Elephant Listening Project. Payne believes that elephant calls containindicators about health, behavior, and reproduction. If monitoring networkscan be made to recognize those indicators—and Payne and her colleagues areworking to do just that—then bioacoustic monitoring can be used not onlyfor estimating population size but also for gauging the viability of thosepopulations and diagnosing threats as they occur.

Theirony of acoustic elephant monitoring is that without it, we can’t evenhear much of what the elephants are saying: this invisible world was hiddenright in front of human eyes—and ears—until Payne serendipi-tously discoveredit 20 years ago.

Payne had spent 15 years studyingwhale songs. And then, while she was visiting a zoo in Portland, Oregon,in 1984, she noticed a throbbing in the air. The way it reverberated throughher frame recalled a childhood memory¬¬—low notes from a pipe organ ata chapel near her house had given her that same feeling when she stoodclose by. Days later, she returned to the zoo with acoustic monitoringequipment and confirmed her suspicion: these elephants were rumbling outa steady stream of infrasonic calls that no one had ever noticed, someof them almost an octave below human hearing.

That discovery sent animal communicationresearch—and Katy Payne—off in new directions. “After years of studyingwhales and being able to hear them but not see them,” says Payne, “it wasjust magnificent to spend time actually watching the behavior of thesevery emotional, mutually supportive animals.” And that she did, studyinginfrasonic calls in African savanna elephants. It’s now known that mostelephant calls dip below human hearing, and many of these calls providelong-distance communication.

Payne’s research with elephants continuedover two decades, but it was a burning conservation need—monitoring elephantpopulations for signs of poaching—that turned her attention to forest elephants(see box opposite). So severe is the lack of information on forest ele-phantsthat their worldwide population estimates vary from 24,000 to 209,000.

And so Payne and her team are investigatingacoustic monitoring as a means of keeping tabs on forest elephant populations.They’ve worked in two locations—Dzanga Bai, a rare clearing in the CentralAfrican Republic’s Dzanga National Park where forest elephants congregate;and Kakum National Park, a forest fragment in Ghana harboring a populationof forest elephants that humans rarely glimpse.

Atdaybreak in Dzanga Bai, Payne and her team walk two kilometers of elephanttrail from their camp to the clearing, lugging along computers and cameras.As the clearing opens before them, a cool morning breeze greets them withthe sweet smell of elephant dung. They climb to the observation platformand begin assembling cameras and tripods.

The eight autonomous recording units(ARUs) surrounding the clearing were hung in trees three weeks ago andhaven’t been touched since. Each ARU includes a microphone, computer, harddrive for storing data, batteries, and GPS. The GPS provides precise timingso each ARU can synchronize with other units to pinpoint the source ofa call. Each ARU is programmed to specify which frequency ranges will berecorded, during which times of day, and so on. If ARUs record 24/7, theirbatteries can sustain them for three months. If recording is more limited,say only at dawn and dusk, batteries can last many months.

During daylight, the researchers filmthe clearing with video cameras and visually count elephants every 30 minutes,while digital cameras automatically record still photos every 60 seconds.

Dzanga Bai is where the Rosetta Stoneof elephant-speak is being etched, rumble by rumble and shriek by shriek;this is made possible by the fact that you can actually see the elephantsyou’re listening to—a rare thing with these animals. “From the data thatwe get in Dzanga,” explains Payne, “we can create a model that we can usefor interpreting calls in forests where the elephants aren’t seen at all.”

By “model,” Payne means a statisticalcurve that correlates call rate with elephant group size. Elephant callingis contagious: the larger the ele-phant group, the more often each elephantcalls. The data contain plenty of scatter, but the overall correlation,says Payne, is robust.

This technique—quantitative listening—isalready capable of estimating population size. But Dzanga Bai’s visualdisplay of elephants is also helping Payne’s team develop smarter acousticmonitoring systems capable of automatically categorizing and interpretingcalls.

Take the showdown between Eli andGrey-boy, for example. It included three call types: Greyboy’s shriek,indicating subordinance by an adult male; Eli’s deep-throated rumble, advertisinghis testosterone-charged, mating-primed dominant “musth” status; and thereplies of two females, acknowledging the presence of a musth male. Alltold, these elephants probably use several dozen distinct call types. Acousticsystems that identify the most salient of these call types could go a longway toward indicating the health of a population. “If there’s a lot ofpoaching, you would hear few adult males because in this species they’rethe only ones with long tusks,” says Payne. “If you don’t hear infants,you may guess that there hasn’t been much reproduction. But if you hearthe sounds of reproduction, adult males, females, and infants, then it’ssounding good.”

Thecurrent way to estimate forest elephant numbers is dung counting. Thisis done in Kakum National Park, where forest elephants stay conspicuouslyout of sight. African researchers periodically walk the long ele-phanttrails and count dung piles, but in such a dense forest they can see onlya few meters to either side. By comparison, a single ARU can detect mostelephant sounds within at least one square kilometer.

When estimates from acoustic monitoringand dung counting in Kakum were compared in 2002, they were found, in roughterms, to agree. But Kakum also presented a different challenge: elephantswere periodically emerging from the forest and marauding crops plantedalong the forest margin. Local landowners had cooperated with the governmentto establish

a wildlife reserve in Kakum, but elephant crop raiding threatened to poisonthat spirit. The local elders asked Payne whether her ARUs could help. Theidea was to use the calls of unseen elephants to alert farmers when a cropraid was imminent.

But was it really possible to tellwhen elephants were about to raid just by listening to their calls? Payne’steam studied the problem by laying an “acoustic net” of 11 ARUs along themargin of the forest near the oft-raided crops. During one month, elephantscrossed the acoustic net and raided crops eight times. Although 1,040 calls were recorded, no signature for crop raiding was identified.However, the acoustic net revealed two unexpected things. First, elephantsinside the park were spending most of their time—or doing most of their talking—inhotspots, staging areas from which the elephants departed for crop raiding.And second, a great many gunshots were recorded after dark.

Payne’s long-term goal is to put acousticmonitoring into local hands in order to address local and regional conservationissues. “What we’re headed for,” says Payne, “is the simplest possibleprocedures for monitoring in remote areas of Africa, procedures that localAfrican wildlife officers could follow to deploy the units and retrievedata. The point is for them to find out for themselves what their parkscontain, whether poaching is going on, and how things are changing withtime.”

Although ARUs can now be deployedand retrieved by locals, analyzing the data on computers is less user-friendly.But this problem should be solved by another of Payne’s long-term goals:programming ARUs to identify and count specific call types automatically.Local operators could then dial up the ARUs on satellite phones and betold the number of male musth calls heard in the past week.

Developing digital processes to identifyspecific call types is itself a mammoth project. The team has grappledwith this for two years, but they’re well on the way to succeeding. ChristopherClark, who developed the ARU technology, now heads the Cornell BioacousticsResearch Program, which in itself represents a revolution. “I just hada PhD student analyze half a million hours of whale sounds, which is incomprehensible,” saysClark. “That was possible because we had the software tools. You set upthe batch processes and they just run all weekend.” Best of all, standardPC computers are now fast enough to run such analyses. But developing moresophisticated processes, such as sorting the calls that can be used asindicators of population health, is taking longer.

The question is, when can acousticmonitoring be used by the odd national park or wildlife refuge—specifically,when can it be done on the cheap? The answer, say Payne and Clark, is soon.ARUs currently cost about US$1,000 each to manufacture (the Cornell labbuilds them for collaborators). But as with Pentium chips, MP3 players,and other electronic gizmos, costs are rapidly falling while capabilitycontinues to rise. Better yet, ARUs can be reused season after season,enhancing their cost-effectiveness.

There’s no telling what even a modestinvestment in acoustic monitoring will reveal. This remains just as truetoday as it was on that fateful day 20 years ago when Payne turned on heracoustic unit to discover that infrasonic elephant calls had been hidingin plain sight for the entire history of human-elephant contact.

At Kakum, the team unexpectedly discoveredthat gunshots often occur after dusk. This finding has stimulated the Cornellteam to develop ARU software for automatically identifying gunshots.

Meanwhile, Payne and Clark envisiontaking acoustic monitoring to greater lengths—recording and analyzing thetotal sound representation, or soundscape, of entire ecosystems. Soundscapemonitoring could actually probe biodiversity by recording the sounds—whethersoothing or strident, ultrasonic or infrasonic—of any and all noise-makingcreatures, from bats to elephants. “The wild world is a very noisy place,” saysPayne, “and the better we listen, the more we’ll learn about it.”

EASING THE IVORY BAN

Member nations ofCITES (Convention on the International Trade of Endangered Species) recentlyagreed to ease the ivory trade ban and legalize trade in stockpiled savannaelephant ivory in three southern African nations. The selected nations—Botswana,South Africa, and Namibia—have strong law enforcement for combating poaching.And aerial surveys mandated by CITES help managers detect and curb poachingactivities. But in most central and west African nations, monitoring isdifficult and law enforcement is weak. The legalized commerce of any sortof ivory—whether from stockpiles or live animals, savanna or forest elephants—wouldincrease the incentive for and probably the incidence of elephant poaching.Almost all forest elephants would be jeopardized. Although acoustic monitoringprovides estimates of forest elephant populations and detects signs ofpoaching, it alone cannot protect elephants from poaching. That can occuronly when law enforcement works hand-in-hand with monitoring.

About the Author:

Douglas Fox is a freelance wirter based in San Francisco, California.

For more information

The Elephant Listening Project www.elephantlisteningproject.org

Payne, K., M. Thompson and L. Kramer. 2003.Elephant calling patterns as indicators of group size and composition: the basis for an acoustic monitoring system. African Journal of Ecology 41:99-107.

Payne K., W.R. Langbauer, Jr., and E. Thomas.1986. Infrasonic calls of the Asian elephant (Elephas maximus). BehavioralEcology and Sociobiology 18:297-301.