Scientists Uncover the Physics of the Elephant’s Long-Distance “Seismic Network”

African elephants (Loxodonta Africana) live in the savannas, rainforests, woodlands, and scrub forests of central and southern Africa. In these wide-open landscapes, long-distance communication is a distinct advantage. Whilst elephants cannot pick up a phone to make a long-distance call, they can use the earth to transmit information. Here, we explore the fascinating subject of elephant seismic communication.

How Do African Elephants Communicate?

Female African elephants live in herds of up to 70 individuals. The bulls either live a solitary life or with a few other males. They communicate with each other through body language (for example, the position of their ears), through touch, scent marking, and sound (acoustically).

Elephants can make a lot of different sounds! These include rumbles, trumpets, snorts, roars, barks, and grunts. We also know that they can make infrasonic calls, which are below the human range of hearing. They make the calls as warnings, to locate family members, or to gather the herd together to coordinate movement.

The Wonder of Seismic Communication

The term seismic communication is used when an animal can detect vibrations in the earth. We know that several animals, including arthropods, amphibians, small rodents, and potentially elephant seals, can do this.

It makes sense that elephants would use this type of communication. They can produce low-frequency (infrasonic) calls and have a large mass to press against the ground to detect vibrations. We also know that they have long-range social interactions, so long-distance communication would be very useful for them.

The Physics of Sound

It’s easier to understand this if you realize that sound is actually a series of vibrations. When something makes a sound, waves of energy are sent out, making air molecules vibrate. Our ears can detect those vibrations, and our brains turn them into sound. However, sound does not just travel through air. Solid materials can also vibrate with sound waves.

The crucial fact is that when sound waves travel through the ground, they can often travel further and faster, and they lose less energy. We should not be surprised that elephants, for whom long-distance communication is so important, have evolved to take advantage of this!

Elephant Deep Rumbles

The deepest rumbles produced by elephants can travel over a mile through the air. More importantly, they pass efficiently through soil, especially where the soil is flat. This is exactly what you find in savannas. So, when an elephant makes a rumble, some of the sound travels through the earth. Scientists have demonstrated that elephants can produce Rayleigh waves (a type of surface acoustic wave that travels along the surface of solids). But how do other elephants detect this sound?

Hearing with Their Feet

Biologists have seen groups of elephants freeze and lift a foot just before another group of elephants arrives. Others spread their feet slightly. It was as if they were shifting onto three feet to better detect vibrations in the ground.

Elephant feet have a fascinating structure. They actually walk on their tiptoes with their digit (toe) bones angled towards the ground. Their feet also have wedge-shaped fat pads made of both fatty tissue and elastic fibers. These cushion the bottom of their feet and protect their bones when all that weight is pressing down. However, they have another extraordinary role.

Soft tissue is great at detecting vibrations in the ground. The vibrations cause the tissue in the pads to move a little, and these stimulate sensitive nerve endings. Signals are sent from the nerves to the brain, where they are interpreted. It is also likely that the vibrations can pass up the elephant’s body to their inner ear through the skeletal system. This is called bone conduction. Differences in rhythm, strength, and direction help with interpretation. The elephants are probably shifting their position to remove background ‘noise’ and improve sensitivity.

Using Dual Communication Channels

It is important not to overstate the role of seismic communication in elephant populations. Rumbles have both acoustic (air) and seismic elements, and don’t forget that elephants have big ears for a reason! Hearing is still an important sense for them.

That said, seismic communication is likely to be very useful for elephants. It is probably used to supplement and extend acoustic communication. It could be a useful alternative in some situations. For example, sounds are heard best downwind of the source, whereas seismic sounds spread equally in all directions. Additionally, acoustic waves do not travel so well through dense vegetation, so seismic communication would be preferable in these areas.

Elephants may even seek out areas with a rock subsurface because it gives the best transmission, but there is no firm evidence of this to date. Finally, earth vibrations may help them detect when a herd is approaching or even changes in the weather. Some studies suggest elephants may be able to sense distant thunderstorms, possibly by detecting low-frequency sounds, but more research is needed to confirm how early and accurately they can do this.