A new study led by the Western University in Canada has found that mammals inhabiting the Greater Kruger National Park in South Africa, which boasts one of the largest existing lion populations, exhibit heightened fear when exposed to human voices in comparison to sounds such as lion roars, dogs barking, or even gunshots. Worldwide data indicates that humans prey on other species at significantly greater rates than other predators.
“We usually think about the top of the food chain being large carnivore predators,” said first author Liana Y. Zanette, a conservation biologist at Western University. “But what we’re interested in is the unique ecology of humans as predators in the system, because humans are super lethal.”
“Normally, if you’re a mammal, you’re not going to die of disease or hunger. The thing that actually ends your life is going to be a predator, and the bigger you are the bigger the predator that finishes you off,” added co-author Micheal Clinchy, another conservation biologist at the same institution.
“Lions are the biggest group-hunting land predator on the planet, and thus ought to be the scariest, and so we’re comparing the fear of humans versus lions to find out if humans are scarier than the scariest non-human predator.”
In the course of this extensive South African study, the research team examined the responses of 19 mammalian species to various audio recordings: human voices, lion sounds, barking dogs, and gunshots.
The vocalizations of humans were taken from TV and radio broadcasts in the region’s predominant languages: Tsonga, Northern Sotho, English, and Afrikaans.
The sounds of dogs and gunshots symbolized human hunting activities, while the lion sounds, chosen in collaboration with lion specialist and co-author Craig Packer of the University of Minnesota, represented the apex predator in the area.
“The key thing is that the lion vocalizations are of them snarling and growling, in ‘conversation’ as it were, not roaring at each other,” Clinchy explained. “That way the lion vocalizations are directly comparable to those of the humans speaking conversationally.”
Utilizing specially designed waterproof devices that integrated a camera trap with a speaker, the team was able to record animal reactions for extended durations. These devices were strategically placed at waterholes during the dry season to capture diverse animal interactions, leading to an impressive collection of over 15,000 videos to analyze.
Zanette recalled one memorable incident involving their equipment: “We put the camera in a bear box, not because there are bears out in South Africa, but because of the hyenas and leopards that like to chew on them. One night, the lion recording made this elephant so angry that it charged and just smashed the whole thing.”
The analysis revealed a stark difference in animal reactions to human voices versus other sounds. A staggering 95 percent of species, encompassing creatures like leopards, giraffes, rhinos, and elephants, demonstrated more pronounced avoidance behavior when hearing human voices compared to lion or hunting sounds.
“There’s this idea that the animals are going to habituate to humans if they’re not hunted. But we’ve shown that this isn’t the case,” Clinchy reported. “The fear of humans is ingrained and pervasive, so this is something that we need to start thinking about seriously for conservation purposes.”
Currently, the researchers are exploring the potential of their audio systems in diverting endangered species from poaching hotspots in South Africa. Preliminary results, especially with the Southern white rhino, appear promising.
“I think the pervasiveness of the fear throughout the savannah mammal community is a real testament to the environmental impact that humans have. Not just through habitat loss and climate change and species extinction, which is all important stuff,” said Zanette.
But just having us out there on that landscape is enough of a danger signal that they respond really strongly. They are scared to death of humans, way more than any other predator.”
The study is published in the journal Current Biology.
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