Researchers are listening to Addo’s elephants

The best-known call might be the trumpet, but the most common and important call is the low-frequency rumble.

These rumbles are produced via the vibration of a passive vocal fold when it is stimulated by airflow from the lungs, similar to human speech. Since elephants have massive vocal folds, reaching about 10 to 14cm in adults, these passive vibrations produce infrasonic frequencies, which are below the range of human hearing. However, these sounds also contain audible components that can be perceived by humans when in close proximity to elephants.

A research group from the University of Vienna led by Dr. Angela Stoeger and Mag. Anton Baotic, has been studying the communication of the elephants in the Addo Elephant National Park since 2011. They are interested in various aspects of this vocal behavior, including vocal dialects and individual differences in vocalizations, especially since elephants seem to know exactly who is calling.

As elephants make extensive use of their powerful infrasonic calls for long distance communication, they are a perfect model species for acoustic observation because it is possible to detect them even if they are out of sight. As such, the Vienna research team is exploring the use of elephant vocal signals to monitor their movements.

Some of their first published results have showed that it is possible to estimate age groups of African elephants based on acoustic parameters extracted from the low frequency rumbles. The rumbles of calves are higher in pitch than from juvenile and adult individuals and can be clearly discriminated.

Such findings can have important implications for the conservation of this iconic species. The new insights about acoustic age classification may help to provide information on herd demographics, distribution and densities.

However, researchers are also testing whether it might be possible to use vocalizations to regulate elephants

impact on the surrounding biodiversity, by manipulating how these large mammals use the space.

The idea is to play certain calls (for example alarm calls) back to them, to induce spatial and temporal variation in the intensity with which elephants use landscapes.

Before this can be tested, the researchers need to understand the meaning of particular vocalizations to them.

In order to do this, they are conducting playback experiments. This involves two research vehicles driving around Addo, one of which is equipped with a custom-built subwoofer that can produce infrasound. This vehicle is hidden behind trees outside of the view of elephants, while researchers in the other car document the behavioral response to the infrasound.

These experiments have demonstrated that elephants respond differently to human- and bee-induced alarm rumbles. The ir responses are population specific, as elephants adapt to threats that are of particular importance for them. For instance, a female group with calves will probably react differently to particular alarm signals or other kinds of threat signals than a group of young males, or a musth-male (a male displaying rutting behavior).

It will therefore be crucial to investigate differences in behavioral responses of various individuals and groups of elephants. The Vienna research team is optimistic that the idea of an acoustic monitoring and deterrent

system is feasible and can be implemented in the future, but years of research will still be necessary in order to develop the fundamental knowledge about elephant vocal behavior crucial to this intended system.