Elephants, rhinos, and other African mammals are far more scared of hearing human voices than lion vocalizations or even hunting sounds, a study has found.
The findings, published in the journal Current Biology, have shed new light on the ecological impact of humans on the natural world, according to the researchers.
Ecologists recently began describing humans as a “super predator” because new global surveys have documented that our species kills prey at much higher rates than other predators, in comparison to other animals like lions, leopards or wolves.
“Given the new surveys showing humans are far more lethal than other predators, wildlife’s fear of humans may be expected to be far more powerful and all-prevailing and consequently have far greater ecological impacts,” Michael Clinchy, a conservation biologist at the Western University in Ontario, Canada, and an author of the study, told Newsweek.
Clinchy and study co-author Liana Zanette—another conservation biologist at Western—are part of a lab at the university whose research focuses on the “ecology of fear.”
“Predators kill prey, and that obviously reduces prey numbers, but what we’ve demonstrated in other work is that the fear predators inspire can itself reduce prey numbers—for example, because fearful animals have fewer chances to eat and so produce fewer young,” Clinchy said.
“In parallel with the work reported in the present paper, we’ve now begun demonstrating that fear of humans can itself have cascading impacts on wildlife communities.”
In the study, the researchers wanted to experimentally test how fearful wildlife are of humans versus what many consider to be the world’s most fearsome non-human predator: lions.
“Lions have long been seen as the world’s most fearsome land predator—the ‘king of beasts’—which makes good ecological sense because they are the largest group-hunting land predator on the planet,” Clinchy said. “So that’s why we’re here experimentally testing wildlife’s fear of humans compared to lions, to best gauge just how large the impacts of the fear of us may prove to be.”
The researchers traveled to South Africa’s Greater Kruger National Park, which is home to one of the world’s largest remaining lion populations. They then went to waterholes, where prior research has shown that lions do much of their killing.
“The setting then is that we’ve gone to where there are more lions than anywhere else, and we’re at waterholes where the local wildlife are in greatest danger of being killed by lions,” Clinchy said. “Hence we’re not just comparing the fear of humans versus lions, we’re doing so where the fear of lions should be at an absolute maximum.”
At each waterhole, the researchers set up a hidden automated camera-speaker system that was triggered by animals passing by within a distance of 30 feet. When triggered, the system filmed the response of the animal to hearing either humans speaking calmly in locally-used languages; lions snarling and growling; hunting sounds, such as dogs barking or gunshots; or non-threatening bird calls.
Importantly, the human voice clips were played at conversational volume levels. The lion vocalizations used, meanwhile, were snarls or growls—comparable to humans speaking conversationally—rather than roars.
The camera-speaker system was operational for six weeks during the dry season, filming the responses of every type of animal that came to drink. This amounted to 19 different species in total, including giraffes, leopards, hyenas, zebras, kudu, warthog, impala, elephants and rhinoceroses.
The researchers quantified fear in two ways: by determining whether the animal ran in response to a playback sound and by measuring the time it took them to abandon the waterhole.
The team made a number of key findings, the first being the “very substantial” degree to which fear of the human “super predator” exceeded that of lions, Clinchy said.
As a whole, the Kruger wildlife were twice as likely to run and abandon waterholes in 40 percent faster time in response to hearing human voices compared to hearing lions.
The second key finding was the comprehensiveness with which the greater fear of humans pervaded the community of savanna mammals with around 95 percent of species running more often or abandoning waterholes faster in response to humans than in response to lions.
Another important finding was that specifically hearing human vocalizations inspired the greatest fear rather than the hunting sounds. This suggests that wildlife recognizes humans as the real danger, whereas related disturbances such as barking dogs are merely lesser proxies.
The fourth key finding is that this “powerful and all-prevailing fear of humans is evident even in one of the world’s premier protected areas,” Clinchy said. And the fifth is “that this is occurring where fear of lions can be expected to be maximal.”
“Our results demonstrate that fear of the human ‘super predator’ far exceeds even that of the most fearsome non-human land predator on the planet, the lion, and can pervade entire communities of mammals, even in protected areas,” he said. “This is consistent with the new global surveys documenting humanity’s unique lethality, but not known before we conducted this critical test.
“On one level, the results are consistent with humans as a ‘super predator’ and so not surprising, on another level, they are shocking. What I find shocking is thinking through what is actually happening here: an African savanna mammal is coming to a waterhole for a drink and hears just 30 feet away from apparently behind a tree, the sound of a lion or a human, and is twice as likely to flee in terror from the human!”
The very substantial fear of humans demonstrated in the study, and in comparable recent experiments, can be expected to have dramatic ecological consequences, according to the researchers.
“The implications of these findings present a significant new challenge for protected areas management and wildlife conservation because it is now clear fear of even benign humans, like wildlife tourists, can cause these previously unrecognized impacts,” Clinchy said.