Elephants are intensely social animals, and while their trumpeting calls are a familiar sound to most of us, elephant communication is much more complex than it seems. Researchers have known for some time that elephants have another more subtle way of communicating: low-frequency calls that cause vibrations in the ground. And these tactile signals can travel even farther than air-borne, audible calls, according to a new study, published today in Current Biology.
The low-frequency noises—also known as infrasound—that elephants make are generally too low for us to hear, according to Beth Mortimer, a research fellow at the University of Oxford and lead author on the new study. But even humans can often feel the powerful sounds (often as a vibration in the diaphragm).
Mortimer and her colleagues spent three weeks in the field in Kenya in 2017, using geophones—a technology developed to study seismic signals from things like earthquakes—to detect and record vibrations made by wild elephants. The team used computer algorithms to transform the recordings into visual representations of the seismic signals. They found that different behaviors, such as running, walking, or vocalizing, generated distinct patterns. In other words, the researchers could remotely detect what elephants were up to based on the movements picked up on recording devices, even from more than half a mile away.
Mortimer was taken aback by the finding that vocalizations were even easier to detect using this method than locomotion. "I was surprised that the vocalizations generated such a huge amount of force," she says. The study provides researchers with an exciting new way to study long-range elephant communication, but the authors also found that even vocalization signals could be drowned out by human-generated sounds, such as the noise from cars.
Still, elephant populations in far-flung or remote areas are the hardest to protect from poachers, who have devastated African elephant populations. In these regions with less anthropogenic noise, networks of geophones could allow both researchers and conservationists to monitor elephant behavior from afar. When elephants encounter danger, they often emit warning calls and run—both behaviors that generate these subtle seismic signals. Humans are one of the only threats to adult elephants, and remotely sensing these distress signals could help conservationists thwart poachers.
Of course, this study is just the first step: Much more research is needed to determine just how far these signals can travel before a practical monitoring system could ever be deployed. But time is running out. Even as officials around the world crack down on the illegal ivory trade, in many places, elephant populations continue to fall.