Science Sound(E)scapes: Amazon Pink River Dolphins

Full Transcript

This is Scientific American’s 60-Second Science. I’m Jeff DelViscio. 

Today we’re going to do something completely different: We’re going to offer you a break in the pandemic and politics by taking you on a three-part sound journey to the Amazon. We will eavesdrop on some incredible creatures in the world’s largest rain forest. Think of it as a soundscape turned into a sound escape. 

Today episode one: into the river. Our guide for this audio trip is Tim Weaver. Tim is a professor of emergent digital practices and a multimedia and sound artist at the University of Denver. Thanks for joining us, Tim. 

“Thanks, Jeff, for that intro. We’re going to be listening to some far-reaching soundscape ecologies today from research that I’ve been conducting off of the main stem of the Amazon on the Peruvian border with Brazil.”

Tim, could we start out by talking a little bit about what you do? Tell us about soundscape ecology.

“One way of looking at ecological stability, or what’s happening in the dynamics of ecologies, is by looking at the sound of spaces, or the acoustic ecology. It’s a newer area, in terms of looking at an exchange of information in ecologies and diversity. And with recording technology, there’s amazing ways to look at this. And so we’re looking at everything from the resonances of forests—so how does a forest that has been cut sound? And how does sound reflected into a native forest that still has its native, somewhat intact, primary forest—communication between species. So bioacoustics is a big piece of it, as well as the resonance of the forest—how things reflect. 

“And the tools that we use are everything from recording in three-dimensional sound with new innovative multiple microphone devices so we can record somewhat three-dimensionally with microphone arrays. We’re using hydrophones underwater and just standard stereo microphones that we can deploy and then also some that we can schedule and leave out there for up to a month and go back and get them and bring them back in and then analyze the soundscapes and the communication going on with artificial intelligence. So we’re using all those tools in our research.”

Now let’s talk about some of that research, specifically, into the pink river dolphin. The pink river dolphin is now endangered. I guess you had a hard time actually finding them, right Tim?

“So this is about 140 kilometers upriver, on the main stem of the Amazon in a side tributary. This event is recorded the same time of year that Jeff and I are having a conversation in October/November. And the Amazon river is rising, then, from the runoff from the Andes. There’s a lull in it, so it’s coming  up. So what that means is: there’s migratory catfish coming all the way from the mouth of the Amazon—all the way up to this interface with the Andes and where the upper Amazon drops—and then they’re laying their eggs there. It is one of the largest migrations of fish in the world. And with that, pink river dolphins want to go in there, and it’s a great time to go in pods and maybe with their young and slurp up these catfish eggs or other types of fish.

“The interesting thing about the pink river dolphins is they then go into the forest to hunt, which is wide open. And with that, they’ve evolved from being toothed whales. When the Andes rose up, they were trapped in the Amazon and evolved. And they’re obligate freshwater; they’re not saltwater at all, and they can also flex their bodies almost in half to get around trees and things like that. They’re different from ocean dolphins in that their beaks are longer, and they have small cilia, or small things to feel on the end of their beaks. And it’s a very low visibility environment, so they’re communicating by echolocation.”

A drowned Amazon forest is a difficult place for them to move, so how did you get into position to capture them on tape?

“We go in with small boats and the water hyacinths and everything being pushed down the river tributaries. You’ve got to hack your way through it. Once you get into the oxbow lakes, which change every year, the dolphins can operate in there really well. They tend to hang out in there as the water comes up. And it will rise 20 to 30 feet to submerge the forest. Then they can go to the forest and then come out.

“I’ve been down there multiple seasons to record and over four different times of field recording down there. I’ve gotten 10 seconds of recording, 30 seconds recording. And in the last time, when it was just the right moment where they’re going into start to hunt in these fish nests, I got five hours of recording.”

So what are we actually hearing when we listen to the audio?

“So there’s a mixture of sounds, and there are not surface sounds. It’s recorded with a hydrophone. On the surface, you’re hearing the dolphins. And a lot of people that have seen dolphins when they come up for air—they are mammals—you’ll hear the blow happen. But when they go subsurface, then they’re communicating in this whole array of more ultrasonic sounds, so we’re catching the edge of that. But there’s also sounds of croaking of—Amazonian freshwater fish are not well characterized—what should be catfish that we’re hearing. So you’re hearing this kind of mixture of croaking of these fish and then communication of the dolphins to pinpoint where there’s really good things to eat.”

You said at the beginning they are a very endangered species. Do you have a feeling that making these recordings is important because maybe, as a species, they might not exist in the future?

“The pressure that’s going on right now is kind of astounding. And it’s happening all over the Amazonian basin with the countries there, so Brazil, Peru, Colombia, Venezuela and then all the way down into Bolivia as well. There’s a lot of colonists that have gone down to the Amazon basin because they’re landless, and they want to farm catfish because there’s a big market for them.

“So the biggest piece of protein to put in that aquaculture is pink river dolphins. So they’ll shoot them or hack them up into bits and raise catfish, then send them out to any export market, maybe in Columbia or something like that. And that’s happening all over the Amazon basin right now. It’s kind of horrific, and you see these beautiful animals, and you know you can see them surface. And it’s pretty remote down there, so it’s hard to enforce. It’s definitely illegal in Peru to kill a river dolphin, but it happens. So we’re trying to raise consciousness with these recordings and then bring this into new works, creative works and scientific works to start to document that.”

Let’s stand back and let the dolphins speak for themselves. 

[CLIP: Dolphin sounds]

Thank you, Tim, for sharing your work with us in the 60-Second Science podcast 

“Thank you, Jeff. And I hope that everybody can gain a perspective of the sounds around us—and also that incredible possibilities for listening and the diversity of acoustic ecologies on our planet.”

And thank you to all the listeners for taking this trip with us. Make sure to join us for the next episode of this Amazon sound escape, coming soon to the podcast. In the next episode: inside the dark embrace for the rain forest night.

[The above text is a transcript of this podcast.]