Elephants are very vocal creatures, yet humans remained unaware of this until 1984, when Katy Payne discovered that often their communication happens below the threshold of human hearing. At the Dzanga Bai in Central African Republic, ELP researchers estimated that we may only hear somewhere around 40% of all the calls elephants produce. Mostly this is because the higher, human audible, frequencies rapidly attenuate in the warm humid air. By the time a call has traveled 50-100 meters, only the lowest, inaudible frequencies are left.
An Elephant “Dictionary”
Although our research is still just scratching the surface of forest elephant communication, the goal of a new research project at Dzanga bai, Central African Republic, is to match certain types of calls with behaviors to build a sort of “dictionary” of elephant vocalizations.
With the help of acoustic recorders in the forest and video taken at forest clearings, we have begun compiling this call-behavior dictionary. Some calls are especially distinct, such as greeting and distress calls, while others have meanings that we still struggle to interpret. We believe that very complex information is acoustically communicated, including emotions, physical characteristics, intentions, and even references to abstract concepts. Certain calls also carry information about family and individual relationships.
Elephants are capable of making extremely low frequency and powerful calls — sometimes as loud as construction tools (90 to 117 dB Sound Pressure Level). Under the best ambient conditions, these low sounds carry over distances of several kilometers and might enable elephants to stay in contact despite separation in the dense rain forest. The trick to learning what information these calls contain is to pair visual observation of their behaviors with knowledge about who is producing which calls. From there we can begin to tease apart how the sounds differ from one another. But because sometimes the calls are not audible, and elephants can produce rumbles and other sounds both through their mouths and through their trunks, we need to use an “acoustic array” to locate who is making the calls.
The video below shows how we can put these various sources of information together to better understand the complex interactions that we observe in forest clearings. This elephant family heard something startling in the forest and panicked a little bit, running to the edge of the clearing and huddling together. From 50 meters away we could only hear the very first rumble given by the matriarch. But using an acoustic array we could match elephants to the rumbles we recorded. As each rumble appears on the spectrogram at the bottom right edge of the video, we have circled the elephant producing that call.