The scariest sound in the savannah

But first, to South Africa now, and a new study into the ecology of fear. The most terror-inducing sound in the whole of the African plains has been identified by researchers working in Kruger National Park. Will Tingle has the story...

Will - Take it from me: the soundscape of the South African Savannah contains many noises that might put the chills into you. From the strange roar of a lion to the unearthly hoot of an owl. And of course there are other noises to be wary of, but none of those inspired the most fear into animals. There is one more noise that causes mammal species to flee like no other. And if you haven't already guessed, it's this.

Speaker - My dad was a teacher, so I grew up in a home where everything I knew was sports. I played tennis, I played cricket, I played rugby. I loved my sports, especially cricket and rugby.

Will - Regular human conversation. Now I'm terrible at small talk, but not enough to flee for my life. But this is the case for nearly all of the mammals that use waterholes in the Greater Kruger area of South Africa. I spoke to lead author Liana Zanette from Western University Canada about what kind of fear normal human chatter can instil.

Liana - It was remarkable. Across the mammal community, 95% of the wildlife responded two times more fearfully to the humans, and they left the waterhole 40% faster than they did when they heard even lions.

Will - The implications of this are huge for several reasons. Not only has human speech been identified across a number of individual species, it has been singled out as one you can't afford to be anywhere near. And the question as to whether this fear is innate or learned is very difficult to answer. Naturally, awareness of predatory noise spreads quickly through a community, but there are also studies that say certain prey species fear the sound of predators that have been extinct in that area for sometimes many, many generations. All we can say is that fear of humans is a worldwide, deeply ingrained phenomenon. But the African bush is full of noises, birds, insects and what have you. So how do mammals in Kruger know what they're hearing is definitely human?

Liana - Because we talk a lot!The nice thing about using lions versus humans is that we're really quite similar in a lot of ways. Humans and lions have been competitors for prey for millennia, but also lions are large and they're group hunters. Humans are the second largest predator out there and we also are group hunters, but also lions talk a lot. And so it's not going to be anything unique. Prey are going to have experienced humans as predators forever. It's part of their evolutionary history. What's unique is our ecology as predators. We do lethally kill a lot of different species and what the wildlife out there is telling us is that they recognise this and they're not stupid. So if you have a dangerous predator that is 10 metres away from you, you do not hang out in the neighbourhood. You run and that's exactly what they do. They run or they leave the waterhole.

Will - They're still very well. So being fearful and therefore wary of a predator is surely a good thing, right?

Liana - Just the fear of predators can have effects on population numbers because scared prey eat less, so they're going to produce fewer offspring. We've shown in experiments that thinking that there are predators around does lead to 53% fewer kids that parents are able to produce. If fear of humans to this extent really does pervade the planet, then it really does at a new dimension to our worldwide impacts that we're having on the environment. Our mere presence on the landscape could be having enormous effects as well.

Will - The idea that just the presence of humans alone is driving down successful breeding rates in animals is definitely cause for concern and something to be considered for future conservation schemes. But there may actually be a way for conservationists to use this to their advantage.

Liana - The good news story, though, about all of this is that it's kind of the flip side. What we're interested in looking at then is whether or not we might be able to use fear of humans as a conservation tool to protect species. So for example, rhinos? In some of our work in South Africa, we show that those rhinos do not like it when they think that people are around. They flee and they leave the waterhole. And rhinos are really heavily poached in South Africa and it's possible that what we might be able to do is go to areas where there's heavy poaching, illegal hunting of rhinos and play something that rhinos do not like, which is humans talking, to keep rhinos out of those areas where they are heavily poached. There has been some research that shows that rhinos, on a long time scale, will stay away from areas where speakers have been set up and people are speaking. Thinking about the flip side is always a good thing.