NEW YORK (NYTIMES) - With a trunk that produces 110-decibel blasts that can be heard for miles, elephants are well-equipped for long-distance communication. But it turns out they may be letting their feet do some of the talking, too.
Using tools designed for detecting earthquakes, researchers found that different elephant activities - walking, running, snorting, grunting - create distinct "seismic signatures" in the ground.
In some cases, according to a study published on Monday (May 7) in the journal Current Biology, these vibrations travel farther through the ground than they could through the air, giving the animals a variety of powerful methods for long-distance communication.
"It's not surprising that walking affects their vibrations, but they're so big that their snorts and grunts also generate very low-frequency vibrations," said Dr Beth Mortimer, a biologist at both the University of Oxford and the University of Bristol and lead author of the study.
"And by monitoring the vibrations through the ground, we could determine what the elephants were doing."
Earlier studies have shown that elephants may be monitoring ground vibrations through their bodies, a trait more commonly associated with small creatures such as scorpions and insects.
For example, elephants have been observed fleeing for higher ground in the moments before distant tsunamis, and a mother elephant who feels threatened will stomp on the ground to warn others away.
By suggesting that elephants not only cause distinct vibrations with different activities, but can perceive the difference from great distances, the research expands the possibilities of what the animals may be communicating.
It also presents a new opportunity for researchers and conservationists looking to surveil the animals at a distance, a tactic that could be useful for saving a species that is threatened by poachers.
"What we've shown is that we can basically use this as a remote monitoring strategy," Dr Mortimer said.
Despite international efforts to ban the trade of ivory dating back decades, tens of thousands of African elephants continue to be killed for their tusks every year.
To conduct the study, the researchers planted devices known as geophones near wild elephants in Kenya.
Like seismographs, geophones convert ground vibrations into measurable electronic signals, but are smaller, lighter and better suited to field work.
With these tools, researchers hypothesised that they could, "triangulate where different seismic forces are coming from," to track and protect the animals, Dr Mortimer said.
The researchers then used computer models to show that the vibrations they recorded could be detected and distinguished nearly 6.4km away under optimal conditions.
By comparison, an elephant's trumpet can typically only travel about 3.2km through the air, Dr Mortimer said.
Optimal conditions are tough to come by in a world of noisy humans, however.
"Any kind of noise pollution that's vibrating the ground, even car noise, dramatically reduces the ability to detect and discriminate these vibrations," Dr Mortimer said.
And that may put elephants at more risk than they already face.
Because they live in complex, spatially separated communities, elephants depend on long-distance communication to survive.
Ground vibrations may be used to warn one another of danger, and also to find mates during an elephant's very brief mating period.
"For elephants to find one another, they need to be able to advertise their fertility," Dr Mortimer said.