Human Voices and the "Ecology of Fear"
Air Date: Week of October 20, 2023
Giraffe converge around the watering hole, similar to the set-up for Dr. Zanette’s study. (Photo: Konstantin’s Europe and More, Flickr, CC BY-NC-ND 2.0)
A new study finds that giraffes, zebras, warthogs and impalas are far more afraid of human conversation than even the growls of lions. Lead author Dr. Liana Zanette of Western University in Canada joins Host Aynsley O’Neill to explain how her research provides new insights into the “ecology of fear.”
O’NEILL: Well, prey animals like impala don’t have many tricks up their hooves when it comes to evading human hunters. We are fearsome and lethal predators and they know it, according to new research. A study published in Current Biology found that giraffes, zebras, warthogs, and impala are far more afraid of human conversation than even the low growls of the “king of the jungle”.
[LION GROWL SFX]
O’NEILL: Elephants in the study approached and even attacked the speakers that were playing these lion sounds, but they turned tail and ran when the speakers played human voices. Lead author Dr. Liana Zanette is a Professor of Biology at Western University in Canada, and she’s here to explain. Hello and welcome to Living on Earth!
ZANETTE: Hello, thank you very much. It's a pleasure to be here.
O'NEILL: So your work as a population ecologist focuses on something called the ecology of fear. How would you describe what that means?
ZANETTE: Yeah, the ecology of fear is about predator prey interactions, right, and that's what I work on. But when we think about predator prey interactions, we typically think about how predators can affect prey in terms of the killing that they do, right? Because a lion goes in and it eats a zebra, and then that one means one less zebra in the population. But the ecology of fear looks at predator prey interactions in a slightly different way. And it recognizes that precisely because predators are lethal, predators also scare prey, right. And so prey then mount all kinds of behavioral responses to avoid getting killed. These are responses that we call anti-predator behaviors. And it's stuff, it's just basic stuff like running away from the predator, right? If you think that a predator is in an area, you don't go there, right? So you distance yourself from a predator. And also things like if a predator is in the environment, you know, you have your head up looking for the predator attending to it, which means that you can't have your head down looking for food at the same time, right. And so what we've done in our lab is we've done field experiments that have shown that when animals think that there's predators around, they do feed less, that means that you produce 53% fewer offspring, fewer babies, over a breeding season, and then that in and of itself, fear in and of itself, can actually reduce population numbers, right. So predators don't actually need to kill a single prey in order to affect their population numbers. Just scaring them, does this.
O'NEILL: And so a lot of these previous studies looked at an animal's fear of animal predators. And, as you say, it impacts behavior and even population. But the latest research has to do with human presence and the impacts of human presence on the animals in the savanna. Can you tell me a little bit about that work and what you discovered there?
ZANETTE: That work was done in South Africa, inthe greater Kruger region. And going to South Africa was perfect for this because it is home to one of the world's, if not the world's, most fearsome large carnivore predator, right, lions, that's why we call it, the king of beasts. And they are formidable predators. Partly because they're big, right? They're the biggest predator out there on the savanna. Tigers in the world are bigger, but tigers are solitary hunters. Lions are the biggest carnivore on the savanna, and they also group hunt, and that is partly what makes them formidable. And then the other aspect of it was that we were able to set our study up in the dry season at waterholes. And the importance of that is that the dry season means that there's not a lot of, you know, extra water around and so animals have to go down to the water holes to drink. So on the one hand, we know that we're going to get a wide variety of animals. But secondly, the water holes are where lions do a majority of their killing. And so if animals are going to be afraid of lions, right, it's going to be in this area with the largest lion population at these water hole,s so they, animals in this area, should really be definitely afraid of this fearsome predator.
O'NEILL: And so what was the setup of the experiment? How did you figure out who's the most fearsome predator?
ZANETTE: Yes, so to do that, we put a camera up, we secured it to a tree at a waterhole. And then we use the video feature of the camera trap, which was activated when the animal walked about 10 meters pass. So it's going down the water hole at about 10 meters, it triggers the camera that triggers the video that allowed us to gauge the behavior. And then that triggered a custom built speaker that we designed in our lab, which is set above the camera trap. And the speaker would then play a 10 second sound, so that when animals were 10 meters away, they would hear a 10 second sound of either humans talking, and this is just humans talking and conversation at normal decibel levels. So it wasn't, you know, at normal loudness, so it wasn't humans whooping and hollering and stuff like that. It's just people talking in conversation like we're doing now. And we looked at their behavioral responses. And then we compared that to what they did when they heard the sounds of lions. Now, in this case, we didn't use lion roars, which is what most of us are familiar with partly because that's a really loud vocalization. The other thing is that it's meant to travel really far to communicate really far distances to other lions. What we did instead was use snarls and growls, because these are the sounds that lions sort of make when they're kind of chit chatting at one another. Right? And so we could compare humans talking from 10 meters away, versus lions talking from 10 meters away.
O'NEILL: And so what differences did you see, if any, between an animal's fear of these lions versus an animal's fear of humans?
ZANETTE: We found their results really quite amazing. One of the reasons for that is because of the magnitude of the effects that we observed. Because what we saw is that the fear of humans, as predators, really exceeded that of lions, right — the king of beasts and the scary place. The wildlife were two times more likely to run when they heard human sounds, humans speaking, versus lions speaking. And they left the water hole 40% faster when they heard humans. So it's a gigantic result, right? Like, they are telling us that the predator that they most fear are humans. And the other aspect of it was the comprehensiveness of the response. Because we saw this across the 95% of all of the different mammals that we surveyed right, from the smallest to the largest to the carnivores, as well. And so it was really pervasive across the savanna community. And I think another aspect of it was that we were sort of able to pinpoint that it was really hearing humans speak, per se, that was the thing that inspired the most fear here. Because a couple of other treatments, a couple of other sounds that we used, were sounds that are associated with human hunting. So we used gunshots and dogs, but the wildlife responded much less to those sounds than they did to humans, indicating that the signal of danger that wildlife are understanding is the human voice. And that when humans are out there on the landscape, that is something that you have to be frightened of, and you better leave if you don't want to die.
O'NEILL: So I live in the Boston area, and every time I walk near the Charles River, I see flocks of Canadian geese. And from what I can tell these geese are not afraid of people. If anything, I think it's the other way around. I think I'm a little afraid of them. How do some animals like geese learn to be unafraid of humans, while others like the savanna animals that you studied, remain terrified?
ZANETTE: Well, what I would say to that is that you need to do the test on those geese in order to be certain that they're not afraid because we have been fooled by this in the past. For example, we did this experiment on European badgers in the UK. We know from the global surveys that medium sized carnivores, like badgers like raccoons that we have, you know, in North America, like foxes, those medium sized carnivores are killed at five times the rate at which their large carnivores, large carnivore predators kill them, right. So humans are lethal to medium sized carnivores. That includes European badgers. Because humans are a super predator of medium sized carnivores, we would expect badgers to be totally afraid of people, right. But then on the other hand, like you say, badgers live in a completely human dominated landscape. Right? It's in the UK, it's been totally human-dominated for what a millennia or two, right? And so you think then, that living with us, living amongst us for so long, you know, you think that they kind of grow to like us. And that they're kind of used to us, and they think that maybe okay, these humans, they're okay. Otherwise, why would they be living with us?
ZANETTE: But what we found was the total opposite. That even though badgers are living amongst humans, they do not like humans. And that the predator that they were most afraid of in the UK were humans far beyond any of the other conceivable large carnivores out there. And it turns out that animals that we see in urban kind of suburban environments, certainly they live with us, but chances are they do not like us.
O'NEILL: What are the implications of your research for conservation efforts around the world? I mean, there's something like 8 billion people on the planet, what does our presence mean for animal fear?
ZANETTE: I mean, if fear of humans does really pervade the planet to this extent, then it absolutely adds a new dimension to the worldwide impacts that humans are having on the environment, right, a new way to think about what humans are doing out there, to the environment. But what we're showing here is that just being out on the landscape is enough to affect the behavior of a multitude of animals, right. And so and we know from our other experiments, that this can affect population numbers. And so one tactic would be to, knowing this, now that we know this, right? What can we do with it? So, for example, southern white rhinos they run when they hear human voices, and the conservation issue with Southern white rhinos is that they are being heavily poached, currently. The situation in South Africa too is an absolute crisis. Poaching has increased over 9,000% since 2008. It has increased exponentially. And this is for their horn. So our idea is to maybe what we can do to help would be to go to areas in South Africa where we know that there's high human poaching. And then what we would do is sort of set up our speakers, and they would play human sounds. And then the rhinos would hear, right, they would hear oh, my goodness, there's all these humans in the landscape. Then there's no way I'm going into that area because it's just too dangerous. And so that would stop rhinos going into high poaching areas and so not get poached.
O'NEILL: Dr. Liana Zanette is a biologist at Western University in Canada. Thank you so much for joining us today.
ZANETTE: Well, thank you very much. It was a pleasure being here.
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