Why do elephants use seismic communication?

Remarkably, one method through which elephants communicate is via ground-based, or seismic vibrations. We know that elephants generate, and respond to, mini-earthquakes to transfer information between each other using vocalisations known as 'rumbles' that concurrently generate an acoustic vibration. Yet evidence for the biological role of these enigmatic seismic signals in the natural environment is lacking. Investigating their biological role is important for understanding how endangered elephants might be affected by changes in land-use, including increasing anthropogenic seismic noise due to infrastructure development.

We have two hypotheses for the biological roles of seismic vibrations for elephants. Firstly, seismic signals could enable long-distance communication at the kilometre scale, beyond what air-borne sound, smell or sight could offer. Support for this is based on theory and anecdotal evidence, for example vibrations in theory propagate further through the surface of the ground compared to the volume of air. Secondly, seismic vibrations could act as a 'back-up' for acoustic signals to promote transfer of information over variable environments at any spatial scale. This is supported by animal communication theory and modelling work, which show that seismic and acoustic components are influenced by different environmental factors such as wind or geology.

To solve this puzzle, we will eavesdrop on the seismic and acoustic signals generated by elephant rumbles. This allows us to understand how information content of vibrational signals changes during propagation, specifically the different influences of environmental factors such as geology, noise, wind direction, and compare to theory. Our second approach will test how elephants respond to seismic vibrations, both when generated by the elephants themselves and via playback experiments that allow us to manipulate the information content. By manipulating the position and noise content of acoustic and seismic vibrations, we can test for the relative importance of information and noise of these two vibration types at close range.

Combined, this will provide evidence to test our two hypotheses. Specially, whether seismic vibrations have biological roles for elephant communication that are dependent on propagation distance and/or environmental factors. If neither is the case, this supports that seismic and acoustic vibrations form one communication mode, which is important for understanding the evolution of vibration communication systems.

Our goal is to understand why elephants use seismic vibrations for communication. In addition to its functional importance, understanding what elephants use seismic signals for will inform decisions about elephant conservation and management in natural and captive contexts, including the challenges imposed on elephants by anthropogenic noise. Through this study, we will also develop novel methods to monitor elephants remotely in real-time by eavesdropping on the acoustic component of their rumble vocalisations, which can aid elephant conservation in the future.