Elephants' heavy footsteps and low-frequency rumblings are so powerful that they can create seismic waves - vibrations that traverse the ground and along its surface. As a result, elephants have developed a sensitivity to these sound waves traveling through the ground, in part because it helps them communicate with each other over thousands of meters. Animals have an inner ear, as well as pressure-sensitive nerve endings in their feet called "Pacinian corpuscles," and scientists believe these help them detect seismic vibrations.
Now researchers at the University of Oxford and Save the Elephants have found evidence that African elephants (Loxodonta africana) also listen to and respond to ground vibrations created by human activity. The study, published recently in the Proceedings of the Royal Society B , shows that when elephants perceive such human-generated seismic waves, they often move away from them, apparently as a risk avoidance strategy. Previous studies have shown that they avoid the acoustic sounds of bees, the growls of tigers, human voices and the alarm calls of other elephants. But it was not clear if they could also identify and choose between different sounds coming from the ground.
Conservationists fear that the noises generated by global activity will interfere with the signals elephants receive from the natural world and impact their survival. A profusion of low frequency noise is of particular concern in Samburu, where this study was carried out, as it is close to an artillery range. Elephants may also be susceptible to seismic blasting for oil exploration, which is currently taking place in Kavango in Namibia.
To study how they detect and react to seismic waves generated by different sources, Dr Beth Mortimer, a zoologist at the University of Oxford, her colleagues and a team from Save the Elephants released seismic recordings of elephants and noises. human-generated, as well as a combination of the two, to wild elephants in Samburu National Reserve and Buffalo Springs National Reserve in northern Kenya.
When researchers echoed human-made noise (alone or in combination with elephant sounds), wild elephants often froze and seemed to listen vigilantly to these strange sounds. They also moved much further away from sources of human-generated noise than from elephant-generated noise, suggesting that they associated human noise with risk.
"The seismic noise generated by humans is something that the elephants away," said Dr. Mortimer. “This brings us to the conclusion that they associate it with risk. We don't know why - there could be many reasons why they choose to opt out. "
Dr Mortimer said she was surprised to find that elephants pick up human-generated noise, even when combined with elephant sounds. “I expected them to respond only to signals generated by elephants and that noise would mask human sounds, ” she said. “But they took the human-generated part in the combined recording and walked away from it. It was a surprising result, but very important to show that they are getting information from human-generated vibrations. It is not just the seismic vibrations generated by elephants that are relevant to them. "
Noise pollution from human emissions is ubiquitous - and it is only increasing, as is human activity. "Over there, and it is strong and closer, this will affect elephants" said Dr. Mortimer. Even in the relative tranquility of protected areas such as National Reserves, the ground carries human-generated noise from vehicles, generators, gunfire and other sources, which the researchers say new study results, may be enough to disrupt elephant behavior.
"We have shown through this study that the elephants can detect and respond to vibrations caused by man" Mortimer said. "We observed shrinkage of the response to such noise, so we know that human noise poses challenges for elephants because they are so sensitive to ground vibrations. "
Ultimately, Dr. Mortimer believes there is a need for more research to understand how human-generated vibrations affect their well-being. "This study helps to show that elephants use seismic vibrations to a greater variety of information, not only for communication," she said. "We know that seismic vibrations will only increase with time, and we must be aware of the impact this has on the elephants. "
Chris Thouless, Research Manager at Save the Elephant, said: “We still know very little about how elephants use infrasound to communicate with each other and appreciate their surroundings. They operate in a sensory world very different from ours, "hearing" low frequency noises through their feet. They can detect other elephants, distant thunderstorms and sounds of human activity from great distances. This skill helps them survive in a complex environment, but man-made noises can overwhelm even the most subtle signals in the natural world. "
The main conclusions of the study are as follows:
- Elephants can detect human-generated seismic vibrations even when this noise is mixed with vibrations generated by elephants.
- Elephants exhibit vigilant behavior and retreat when these ground vibrations are generated by humans, suggesting that they are responding to them by knowingly engaging in risk avoidance behavior.
- Human-made noises can interfere with the signals elephants receive from the natural world and impact their survival.
Source : Proceedings of the Royal Society B - "Noise matters: Elephants show risk-avoidance behavior in response to human-generated seismic cues"
Watch this short film on how the study data were collected: https://youtu.be/gQe4DR9vcUg