Critically endangered forest elephants use their acute senses of hearing and smell to detect poachers while they are still some distance away and well before they have fired a shot, a new study in the Democratic Republic of Congo suggests.
To gather data, researchers used a grid of 50 passive acoustic sensors that spanned more than 121,000 hectares of Nouabale-Ndoki National Park and an adjacent forestry concession, in the Congo Republic.
They discovered that the elephants went silent shortly before automatic gunfire erupted in eight suspected poaching events.
After the gunshots, elephants immediately increased their vocalisations, suggesting they warned others using alarm signals, or marshalled their family members while heading to safety.
"I mostly expected that we would find a decrease in vocalisations following the gunfire events," said Colin Swider, a doctoral candidate at Syracuse University, who led the study published in the African Journal of Ecology.
"I figured the elephants might immediately abandon the area and head away from the danger, leaving no elephants around for us to detect."
In retrospect, the spike in vocalisations picked up by the sensors did make sense.
"Acoustic communication is a critical part of how elephants overcome stressful or challenging situations together," Swider told RFI. "It is crucial for coordination. I imagine the need to communicate would be quite high following such a dramatic event as a poaching incident."
After that initial spike, however, the elephant calls "dropped to lower-than-baseline rates," the study says. Was this because the animals were simply reducing their vocal activity, or had they moved away?
Elephant soundscape
Swider has a hunch that it is because the elephants move to other areas, away from danger.
He has personal experience that supports this hypothesis. On one memorable occasion while doing fieldwork in 2019 at Dzanga Bai - a natural clearing in the park where forest elephants often gather in numbers of more than 100 at a time - gunshots were heard nearby and all the elephants left.
For days afterwards only a few individuals would appear at the clearing; sometimes none. When elephants did finally return they appeared to be mostly newcomers, oblivious to what had happened.
Other researchers have observed similar responses to trauma. In 2017 a team recorded how forest elephants spent days avoiding the carcass of a slain male elephant at Mbeli Bai, another clearing in the park.
It's unclear whether any of the poaching events recorded by the acoustic sensors, part of the Elephant Listening Project run by the Cornell Lab of Ornithology with the support of an on-site Congolese acoustics team, resulted in the deaths of elephants.
The scientist says upcoming work will combine acoustic grid data with complementary data gathered by anti-poaching rangers from the Wildlife Conservation Society Congo, such as the location of elephant carcasses and other signs of poaching.
But the analysis of the soundscape of elephant rumbles does illuminate the responses to poaching made by this critically endangered species, he says.
"We have shown that poaching has more subtle impacts that seem to ripple into the wider population by affecting behavior of non-targeted elephants."
It could mean that elephants leave areas with high poaching pressure "thereby forsaking otherwise high-quality habitat," the study says.
"In addition to directly killing elephants, poaching could have indirect population-level consequences."
Growing human pressures
The findings are interesting and have implications for conservation management of protected areas, said Andrew Fowler, West and Central Africa director for conservation charity the Zoological Society of London, who was not part of the Congo study.
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Although he has no quantifiable data, Fowler agrees that elephants present in an area where poachers are active will change their behavior.
"I can certainly attest that elephants in areas where there is poacher activity are quiet while still present," he said, adding that he had observed this among forest elephants at two field sites - LuiKotale and Lomako - in the Democratic Republic of Congo.
Even bonobos, a species of ape found at the two sites, went quiet and left the immediate area in the wake of poachers' gunfire, and individual bonobos that were previously used to human presence became wary of observers.
Swider said he hopes acoustic methods like his can be used to collect data to understand the consequences of growing human pressures on wildlife.
"I hope we have stimulated some thought on how acoustic tools might be applied to specific problems or open new avenues of research. And this applies not just to forest elephants and poaching, but to any species and human activity that makes sound."
