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Eavesdropping on Elephants
In Focus, March 2003
Katharine Payne discovered that elephants, like the great blue and fin whales, use sounds below the range of human hearing. Now Payne and her colleagues at the Cornell Lab of Ornithology are designing a new way to capture this infrasonic communication and use it to monitor the size and well being of Africa's elusive forest elephants.
"We've found that elephants make low-frequency, powerful calls that travel considerable distances," says Payne, who studied the songs of whales for 15 years before shifting her focus to elephants. "Now we're testing to see if these calls reflect numbers of elephants, population structures and reproduction. And we're finding that they do."
Payne now heads the Cornell Lab's Elephant Listening Project (ELP), a pilot project that is ultimately expected to benefit not only elephants but other species as well.
Little is known about forest elephants. Populations are low and highly fragmented throughout West and Central Africa, where ivory poaching and habitat destruction pose major threats. Experts estimate close to 10,000 elephants—or only about 3 percent of the entire continental elephant population—remain in the Upper Guinean Forest, where the Critical Ecosystem Partnership Fund is among the project's supporters.
Forest elephants are impossible to survey visually because of the density of the vegetation in their habitats. During a 10-year study in Kakum National Park in Ghana, researchers saw only a few elephants on a handful of occasions. In the same park, ELP researchers never saw a single elephant during a two-month period in 2000 but their special microphones recorded 3,000 elephant calls. The calls, ELP researchers say, were full of information about the population, its size, composition and movements.
Historically, the most reliable information about forest elephants had been based on counts of elephant dung. Now, the team's high-tech eavesdropping from an array of recording units is yielding information to supplement and help interpret the results from traditional monitoring methods.
The basis for the interpretation of elephant calls in unseen populations is drawn from ELP's research in the Dzanga-Sangha forest clearing in the Central African Republic, where elephants are highly visible and present in large numbers. There, in an intensive study using video and acoustic recorders, ELP researchers documented the extent to which calls reflect the numbers and circumstances of the many elephants that visit this clearing. The vocalizations of the forest elephants revealed a wealth of information about group size, composition and reproductive health.
In Ghana's Kakum National Park, recording units with custom-made microphones are strapped to trees and left for two months before being taken back to the Cornell lab in New York. Payne and her colleagues then comb through and analyze the hundreds of hours of audio recordings based on the baseline knowledge about elephants that they gained and tested during their studies in the Central African Republic.
Elephant calls are generally 2-10 seconds in duration with the fundamental frequencies ranging from 5 Hz (in the infrasonic range) to 50 Hz (in the audible range). The infrasound calls can be heard only when the tape speed is accelerated during playback.
One major challenge, Payne says, is to create inexpensive, easy-to-use generic acoustic recording units and methods of analyzing large quantities of acoustic data.
"All of this will be really useful once it is cheap and easy," Payne says. "It has to work in the field. And when it works, we'll have a tool for monitoring not only elephants but also any other vocal animal. In the long run, this should greatly help in the assessment of biodiversity."
Among the project's aims is to create bioacoustics detection and analysis capacities within at least two institutions in the region and to ensure that inter-agency agreements for use of the technology and information are established.
Boon for Conservation
Detection and analysis of elephant sounds, including the infrasonic calls that are inaudible to human ears, will help researchers and conservationists to generate abundance estimates and to deduce population structure from acoustic information. Ultimately, the findings will contribute to management strategies that will ensure the long-term survival of elephant populations.
Targeted conservation outcomes for this project include:
- Elephant populations documented and monitored throughout their range in West Africa, and managed according to previously unavailable information such as population size, age/sex structure, behavior and habitat use.
- Uncommon and understudied wildlife (such as primates and amphibians) identified and monitored in legally established protected areas.
- Acoustic indicators of elephant presence useful in crop raiding prevention.
- An information-rich environment that guides conservation actions in West Africa, built on expanded databases and increased human capacity in Guinean Forests of West Africa hotspot countries.
The project operates under a Memorandum of Understanding signed by Conservation International (CI) and Cornell University in September 2000, which links Cornell's technical expertise with CI's goals and operational capacity in the field. The project involves a variety of CI programs, including the Center for Applied Biodiversity Science, the West Africa Program and CI-Ghana.
But why the Cornell Lab of Ornithology?
The lab is home to the Bioacoustics Research Program, where the techniques being pioneered by ELP are developed. And as Director John Fitzpatrick says, "Our mission explicitly acknowledges that we are here for the protection and interpretation of the Earth's biological diversity. All organisms, large and small, are linked. Elephants just happen to be one of the bigger links."
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© Cornell University, photo by Charles Harrington
Katharine Payne uses computer mapping programs to document the movement and behavior of elephants recorded in Africa.
Update, December 2003: Final project report (PDF)
Two specialized reproductive calls have been identified in African elephants:
- Males, while in the heightened hormonal state called musth, produce very low frequency calls referred to as "musth rumbles."
- Females announce their breeding condition with "estrous rumbles" that are sometimes repeated for up to 45 minutes and can travel several kilometers.
Visit the Elephant Listening Project on the Web.