The Elephant Listening Project

By Melissa Groo

The forests in west and central Africa are thought to contain as many as 300,000 elephants—half of all African elephants. These elephants are at risk due to many pressures including poaching, forest fragmentation, fragile park management, and ongoing illegal trade in ivory. Reliable information about the size, health, and status of forest elephant populations is much needed but hard to obtain because of the dense forest undergrowth. Traditionally the only means of assessing their numbers has been by systematic counting of dung piles.

In 2000, biologist Katy Payne and colleagues launched the Elephant Listening Project (ELP) in order to develop an acoustic method of censusing this African elephant subspecies. Almost two decades ago, Katy had discovered that elephants’ calls are sometimes infrasonic, of such low frequency that they register below our level of hearing. She subsequently carried out studies on infrasound use by African savanna elephants, and determined that low-frequency calls are able to travel long distances, enabling separated group members to coordinate their movements in the same direction, and elephants in reproductive condition to locate one another from afar.

Could acoustic monitoring be used as a conservation tool for forest elephants? Katy Payne and her colleagues thought the possibility intriguing, and in spring 2000, ELP launched an expedition to learn what elephant calls could tell us about population size and health.* This effort was based on historical work in the Bioacoustics Research Program at Cornell University that makes it possible to locate and record sources of sound from arrays of microphones, and process large amounts of data automatically.

The ELP team successfully completed a three-month field season in two African forest areas: Kakum National Park in Ghana, and Dzanga-Ndoki National Park in the Central African Republic. The data ELP collected revealed that the rate of calls at the clearing consistently rose as the number of elephants did. This was extremely important because it meant that elephants’ calls could be a statistical indication of elephant numbers. The data also confirmed that infrasonic rumbles carry at least two kilometers through the forest; therefore, monitoring large areas becomes possible. Further analysis of the data may yield information about the relationship of call types to the group composition and reproductive activity of forest elephant populations.

Future ELP research will seek to refine this method and apply it to other elephant populations, such as the even more endangered Asian Elephants (whose population numbers roughly 30,000). Additionally, ELP will be looking into whether acoustic monitoring may also act as a means of detecting and locating crop-raiding elephants, and/or the gunshots of poachers.

*ELP's pilot year was sponsored by US Fish and Wildlife, International Fund for Animal Welfare, Conservation International, World Wildlife Fund, and the Wildlife Conservation Society.