Unexplainable - A stethoscope for the rainforest

Episode Date: January 10, 2024

Researchers planted microphones in a forest and walked away. Listening back could help heal rainforest ecosystems. For show transcripts, go to bit.ly/unx-transcripts For more, go to http://vox.com/unexplainable It’s a great place to view show transcripts and read more about the topics on our show. Also, email us! [e-mail] We read every email. Support Unexplainable by making a financial contribution to Vox! bit.ly/givepodcasts Learn more about your ad choices. Visit podcastchoices.com/adchoices

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or visit Connexontera.com. I don't know about you, but I am pretty into saving the rainforests. Like, I think people have made a pretty good case for doing so. The Amazon is the largest tropical rainforest and one of the most diverse, biodiverse places on Earth. Home to one in ten species. The rainforest is considered the lungs of the world. It also acts as a major carbon sink.

That means it basically absorbs carbon dioxide emissions. I personally would like the planet to have lungs, and I think it's pretty clear by now that biodiversity is a good thing. Like, if all the plants and animals die, so do we. So, you know, save the rainforests. Except scientists still haven't figured out exactly what it means to save a rainforest. Even ecologists like Yorg Mueller. It's easy to track that the trees are regrowing.

This you can nowadays follow from satellites, It's much more difficult to see if the animals are coming back and how successful is it in term of biodiversity in your different settings, in your different contexts. Part of the trouble is that we don't actually know how many different animal species are supposed to be in most patches of rainforests to begin with. We know rainforests hold millions of species, thousands of birds and frogs, mammals and insects that don't exist anywhere else. But that complex tangle is so under-understood

that we don't really have a great baseline of what a healthy rainforest looks like. It's almost like as if we said, oh, we want to make sure that patients are healthy, but we don't really know what does it mean to be in good health? This is Zuzana Buhlivo. She's an ecologist who's collaborated with York. And she says that treating the rainforest is like treating

sick humans. If we don't have baseline information about what healthy humans look like, how can we then design drugs? How can we design, I don't know, physical therapy? If we don't know, what is the normal range of movement, what is the normal daily life of a healthy person? So that's what York Muller and Susanna Bohievalova are trying to figure out. Like, what does a healthy rainforest look like? What does a healing rainforest look like? And which remedies or interventions are actually helping. It is a big problem. And to solve it, Jorg, Zuzana, and researchers around the globe

turn to a super basic tool, sound. The metaphor that I like the best probably is that we are using a stethoscope. We're trying to listen to the vital sounds of the forest to understand, okay, what does the normal sound like? and then we can detect the problems. This is unexplainable. I'm Bert Pinkerton. And today on the show,

how to build a stethoscope or the rainforest. Yorg Muller's interest in sound as an ecological tool started a little closer to home. Literally. It started in the oldest national park in Germany, which he lives near. And I have the opportunity to go out and enjoy the morning or to see a lynx in my garden

or to have a river order in my fishing pond, something like that is my life. And York doesn't just live next to this charming forest. He studies it. He does stuff like bird counts, where he goes to various spots in the forest and just counts the birds there every year. It's this well-established way to track biodiversity.

But a few years ago, he noticed a problem with this method. I was running around in the forest by myself, making counts of bird in the morning. And already then I recognized it's impossible to be at the same time at every plot. Birds are more active at different times of the day. So anyone who has been woken up by a bunch of birds

knows that they go kind of nuts at dawn specifically. And this worried Yorg, because he knew that if he went around doing bird counts at 20 different plots... Some are before dawn. Others are... are after dawn, you cannot be everywhere at the same time. Which might throw off his data.

Like, maybe he'd count more birds in one part of the forest and another, not because there were actually more birds there, but because he'd visited that first spot at dawn and the other one a little later on the day. So around four years ago, he says he started leaving a sound recorder at each bird counting spot. He left them running and then took short snippets of sound from each one and compared them. the same snips from every plot before dawn, after dawn, and so on. And then you have a selection, which is the same from every plot, and then you listen to them and identify the species.

This refinement had a lot of advantages. Like standardized things, it was fairly cheap. Also, you didn't have humans blundering around, disturbing animals. So just overall, it made these counts easier and more accurate. Seemed like a pretty good stethoscope. And York started to wonder if a... stethoscope like this could be used in other contexts. So he posed the question to Susanna Buhavarova, the ecologist we heard from earlier,

and she specializes in studying animal sounds. And she's something like the rising star, young rising star in sound ecology? Susanna had actually been trying to use animal sounds to measure ecosystems for a while. She'd even done some research using sound to diagnose rainforests. And the science seemed really promising. So, Jorg and Zuzana decided to collaborate on a project focused not on German forests, but on tropical rainforests. The plan was to understand, are forest recovering?

Are they recovering not just in terms of the trees that are growing back, but are they also recovering in the animals that are inside those trees? This is the puzzle that we started with. Yorg and Zuzana basically knew that they could answer this question fairly well in a place. like Germany. It was relatively easy because there aren't that many species of birds and insects in German forests. But in tropical rainforests, there are hundreds of animals making noise, and a lot of them are either understudied or unknown. If you are standing there in the tropical forest, when you are a beginner, it's very hard to

identify all these different species. So in the tropical forests, the first idea was not to identify any species. Vichy. York and Susanna needed a different approach. They turned to one that Susanna had started exploring in her sound ecology research. We use this approach called calculating soundscape indices or acoustic indices. And this allows us to take every single minute of the recording and calculate something about it. We can start monitoring how busy the soundscape is, how complicated it is, How is it changing over time?

Basically, the theory goes that in a healthy ecosystem, you have a lot of different kinds of animals, and they all make different sounds, like high-pitched sounds and low-pitched grumbles. I always like to think of this as if you were listening to an orchestra. If you have lots of different instruments like violins and cellos and flutes, they will all be playing sounds in different frequencies. Whereas if you have just a few species

that aren't occupying all the kind of sonic niches of an environment, it's less of an orchestra and more like a lonely two or three violins. And that violin playing... It will stay within a certain frequency range or pitch. So the plan was to take a bunch of recordings from recovering rainforests, and then measure the orchestras in these areas and sort of see how rich they were.

So we can, for example, calculate, okay, in one minute, how many different frequencies or pitches are occupied? And we call this sound saturation. So if they use a wide range of the space, then we say it's a saturated sound space, not in a spatial sense, but in a frequency sense. researchers have shown that as rainforests are cut down, their soundscapes become less saturated, less rich. Jorg and Zuzana thought that recovering rainforests might rebuild those soundscapes,

and that this could be one way to measure sort of how much biodiversity was healing in an area. So to test this out, Jorg and some of his fellow researchers headed to a lowland region of Ecuador. It used to be rich rainforest, and then settlers came and cleared it for a cowloplin, plantations and pastures. An NGO has been trying to restore rainforest here for several years, working with the local community to regrow, and they want to know if it's working. So, as you can imagine, for a normal forest, recover, to regrow back, it takes decades. So that's why we wanted to look pretty early after the abandonment of these fields, and then a couple years later, and then basically decades later.

So they went in with these little pale gray sound boxes pretty small. They put out these sound recorders into several places in each of these regeneration stages. So in the pasture areas you have very dense cover of grass with a few trees or very spares trees. If you close your eyes and you go to these pasture areas, then you will recognize very, heavy song of birds. So they are very similar. Many of them are small seed eaters like sparrows, buntings, and they love these open field and forage there. So they put soundboxes in these newly abandoned plantations and pastures, and then they put them in plantations and pastures that have been regrowing for a while. You see a lot of bushes, you see some small trees, but it's not

this forest that you can easily walk through. There will be a lot of undergrowth, which will make it tricky to walk through. And finally, they put sound boxes in the parts of the rainforest that had never been cut down, which gave them a baseline, like a sense of what a forest should sound like. You are surrounded by a complex 3D forest

with very huge trees, very dense understory. Huge diversity. of orchids or lianas, so you feel like you're in this bunch of vegetation, there's huge leaves. So it's a totally different world and it's very dark inside the forest. Visibility can be pretty little, but you really feel, as a human in an old growth forest, you really feel kind of buffered from the rest of the world. Yeah. They let those boxes sit, they collected the sounds that you heard, kind of applying their

the scope to the forest. And then they collected those boxes, got the sound files from them. Found was what they expected. And the newly abandoned pastures and plantations that soundscape was less rich, less full. But in the patches that had been recovering for a few years, the sounds got more complex with kind of creatures making noises at more frequencies, which is great. The recordings were helpful-ish. But Zuzana still has questions.

We still don't know enough how closely they should reflect the biodiversity of the species. Zuzana and Yorg, they wanted to know which species were in the forest. Like, for these native species or foreign animals that had come in from elsewhere, their stethoscope was not precise enough to tell them. Like, how could you pick out each individual frog, say,

when there were hundreds of species of frogs, some of which people didn't even have recordings of. It was impossible. Or so they thought, until Yorg went for a walk. Yeah, it's a very nice story. I was walking with my dog at home in the evening. On this walk, he caught up a friend, a former PhD student who loves to Birdwatch,

and he told him about the audio files that he was collecting. And he said, yeah, I was just recently in Ecuador, and I had this field guide there. And he showed me more than 700 species in three weeks. And this is only possible if you know very well the voices. And then I asked him, do you think they would be willing to identify my audio flights? And he said, yeah, why not? After the break, a superhero comes to the rescue.

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Your story could be next. If you've got the drive, they'll help you find your path to the Olympics. Let's see what you've got. Sign up for free at rbc trainingground.ca. Alejandro Arteaga has been wandering through South American forests ever since he was a little kid. We used to live in Venezuela, in a cloud forest, and that's where I grew up, very close in contact with NIC. and just, you know, getting my boots dirty and walking along the forest trails with my brother.

That was my pastime. On those explorations, Alejandra would find animals and learn their names. First insects, then birds, fish. And eventually I capitulated into amphibians and reptiles, which is the main group of animals that I study now. He identified his first new species as a teenager. It was this little brown frog that he distinguished from all the other little brown frogs because it was making weird noises. And over the years, he's built up a rich vocabulary of amphibian croaks and honks.

Like, for example, the call of the smoky jungle frog. A frog that lives in holes, and you almost never see it, but you hear it in the night of the jungle. It's like, whoo? All night, that goes on, on and on throughout the night. And you know the species is there instantly. There's also a tree frog, for example, that's hard to see, apparently, but easy to hear. And you recognize them by this particular sound that they do is like, ah-uh, ah-uh. Nature's squeakiest door, basically.

And Alahandro estimates that he has around 100 to 200 of these kinds of calls, just kind of bouncing around in his head. He's also spent a lot of time in Ecuador specifically. He even wrote a catalog of Ecuador. and reptiles. So he was kind of the perfect person for York Mueller and his team to reach out to when they were looking for help identifying the amphibians in their sound recordings. There are many, many experts of frog vocalizations. I say I'm one of maybe three. So maybe the choice was not so difficult. Either way, Alejandro agreed to help York and his team out, and they sent him lots and lots and lots of recordings. These like two minutes.

sound files drawn from the pastures and the cacao plantations and the old growth forests. And his job was to listen to the files and mark the species he was hearing at various time codes. I like the old growth better. It's more diverse and cooler species. Here we go. Well, this is not going to work because it's in the day. Oh, it's new day. Got it, got it, got it. Let me see if there's anything. from the night. Early morning, sounds like.

That's a poison frog. Wait, wait, wait, wait. Where? The... Okay. That's a poison frog, you said? So, the scientific name is Epipelabatis, Bowling Jedi. The dorsum is like reddish, brownish.

And what is peculiar about this frog is that it carries the tadpoles on his back. You can see them jumping around the wet leaf later during the day. Alejandro sat and listened to lots and lots of audio this way. And he loved it. It's great because it feels like you are back in the forest, which for me is where I belong. So, oh, my God, the sound, the sounds again. But still... It's pretty intense process.

And while Alejandro was listening for... frogs, other experts were listening for birds, too. In the end, they ID'd around 200 species in all. And when they looked at the species in the plantations and the species in the recovering forests, the news was good. Clearly, the regenerating forests are recovering species that are only really found in old-growth forests, which is a really good sign. A good sign. A good for the ecosystem and for the ecologists, right? Like their new tool for monitoring biodiversity, this Alejandro-powered version of the stethoscope,

it was working. But it was still not ideal. In fact, in some ways it still had some of the original problems York encountered when he was wandering through the trees all day, taking counts of birds. Because it still took a lot of time and a lot of highly skilled labor. And it was still not super.

standardized. So York and Susanna wondered, could we make this still just a little bit better? And they had an idea. The idea that we can train a machine to recognize these sounds. Basically, if you say to an AI that learns stuff, hey, this is the sound of a poison frog. And this is also the sound of a poison frog. And here is another sound of a poison frog. Eventually, the AI is able to figure out what all those recordings have in common, and it can filter out the background noise to learn to recognize just the poison frogs trill. Maybe AI could get so good that you wouldn't need Alejandro to sit and listen to hours of audio hunting for poison frogs, right? You could just have an AI do it.

And there was a group called Rainforest Connection that was already pulling together an AI model for rainforest species. So, York reached out and essentially he said, We want to make a proof of your existing model. Why don't we run our files through your model and see how your model compares to our human experts? And they learned that the AI couldn't recognize as many species as the experts, but for the ones it could recognize...

In general, it was pretty good. Their stethoscope still has some pretty fundamental limitations, like this one is tailored to Ecuador. And even with AI's help, it can't track animals that don't make sound. And lots of insects, for example, are pretty quiet. But still, these researchers, they think that this AI-powered version of the stethoscope could change the game on rainforest preservation. When the medical stethoscope was invented in the 1800s,

it helped kick off big changes and how humans took care of each other, Like, the stethoscope alone couldn't heal people, but it helped doctors peer inside bodies without cutting them open. It helped us understand the most fundamental things about ourselves, things we hadn't been able to measure. And that led to better treatments and new cures. Susanna and Jorg's natural stethoscope, it won't treat deforestation or fix fire damage. But it will let researchers listen to, the heart of some of our planet's most important ecosystems, and hopefully help them find better ways to heal them. If you want to read more about Zuzana's work on sound and ecosystems,

look up the Sound Forest Lab. You can also find Jorg and Zuzana's paper on soundscapes in the journal Nature. This episode was reported and produced by me, Bird Pinkerton. It was edited by Jorge Just with help from Brian Resnick and Meredith Hodnott, who also runs our show. Noam Hassamfeld did the music, Christian Ayala, did the mixing and the sound design, along with Erica Huang. Angelie Mercado took the facts, and Manning Nguyen still owes me vacation stories. Special thanks also to Sittlali Morelos Juarez for taking the time to speak with me for this episode, to Liam Brooks for his help, and to Benji Jones for suggesting that we look at this story to begin with. And thanks to Regina Nuzzo, a great statistics professor for her.

help. This podcast and all of Vox is free, in part because of gifts from our readers and listeners. You can go to Vox.com slash give to give today, and if you would, it would be very, very much appreciated. But if you can't, that's also fine. And I would also really appreciate it if you took the time to leave us a review or to write us an email with your thoughts and questions. We are at Unexplanable at Vox.com, and it brings me a lot of joy to hear from you all. Unexplainable is part of the Vox Media Podcast Network, and we will be back next week.