Science Sound(E)scapes: Head-Banging and Howling in the Amazon

JD: This is Scientific American’s sixty-second science. I’m Jeff DelViscio. 

Today, the final episode in our three-part sound escape to the Amazon rainforest. In today’s episode, we’re going into the trees. And be sure to catch the other episodes of this podcast mini-series. The first one was on the pink river dolphin. The second was on the frog choruses. 

Tim Weaver is back with us to finish our Amazon audio tour. 

TW: Thanks Jeff. 

JD: And just to remind you, Tim is a professor of emergent digital practices and a multimedia and sound artist at the University of Denver. Together, we chased pink river dolphins through drowned forests. We’ve taken sonic strolls, very carefully, through the understory awash in frog music. And now we ascend into the trees. Tim, tell us a little bit about where we’re going and what we’re going to find up there. 

TW: We’ve been through three layers of the Amazon: underwater to the forest floor story and now we’ll go up into the canopy. It’s a totally different ecosystem up there and very difficult to record up there but again it’s incredibly bio-diverse. There are mammals that live up there. There’s species that have yet to be discovered up there. And, of course, birds and amphibians lay their eggs up there in the bromeliads. 

So the technology we’re using to do this is a small recorder that can be deployed for actually multiple months so you can schedule to take a recording every half hour from midnight to two in the morning or however you want to sample. And what I was interested in testing these out with was to record howler monkeys, which change their territory every morning. They set the territory before dawn and it’s like the wakening of the world. 

And the other species that’s very interesting in that canopy that is endangered and has gone extinct in North America is a family of woodpeckers called campephilus woodpeckers. They’re the largest in the Americas. They’re about the size of a red tail hawk. They did go from the ivory bills in North America to the Imperials in the Sierras in Mexico, all the way down to Southern Patagonian with the magellanic woodpeckers and this species is a crimson-crested. They’re in the Amazon, they’re in the upper Amazon, in the cloud forests as well, so you’ll hear them drumming on trees. They’re indicative of a very healthy forest because they have to live in a tree that they can have their nests in the middle of so they’re large and these are hardwood incredible hardwood forests, so you’ll hear them drumming. 

This is could be in the afternoon when the howler monkeys reset their territory and it just sounds like this incredible rushing of wind from the Gods coming to you and they clear out to set their territory in the canopy at the same time so there’s an inner dispersion of those two species. 

JD: So how high do you have to climb to place the mics?

TW: So we’re setting them in small trees that are fairly tall, so we can get up into them, not all the way in the canopy, but we can hear the canopy. And they’re above the forest floor so that nothing will climb up the trees and eat them. So if we were in North America, we’d worry about bears eating them; if we’re in the canopy you would worry about things like macaws going down and being curious and cutting them open. So you take a tree that’s a smaller tree, but is tall enough that is about 12 feet off the forest floor, so you can bend it down, set it and then let it come back up. It’s above the forest floor, but the canopy is 150 feet, so we’re getting the animals in the canopy, and their sound coming down to above our own head limit, but it’s not on the forest floor. 

JD: Tell me a little bit about sounding a canopy. We’re so used to hearing sounds that bounce off of hard surfaces all around us without realizing it — walls, ceilings, ground, buildings — what does it sound like when you’re up in midair?

TW: Well, there’s multiple types of reflection going on in the cloud forest and also in the rainforest as well and those surfaces are very waxy. The leaves have a certain geometry and depending on the season, frogs and bats can you use a geometry of the leaves to strategically to hunt with. So if bats are hunting at night they can ricochet their echolocation off of a leaf configuration and find moths that way. 

The length of songs and the wavelength of songs and things like that and communication are really based on those surfaces and they’re very different than a North American temperate forest. So if you were recording and say British Columbia in the Sitka Spruce, the sound will go out and almost doesn’t come back because there’s so much organic on the trunks. And that’s not the case in the Amazon. The trunks of these Cebu trees and things like that are not covered with moss the same way they might be in the North American temperate forest, even though that’s incredibly wet.

It’s also very new territory for looking at ecologies, sound, so we’re really learning about that in so there’s a lot of enthusiastic people doing this work. And these devices were talking about these audio moths are becoming really instrumental that if you can set out an array of one hundred of these and come back in a month and they’ll hold a charge for a month, and they’re really small he can fit them in the palm of your hand, you would gather more data than had ever been taken in relation to this forest, so it’s so that’s good time for doing this work. 

JD: So that’s a lot of data I imagine it’s not exactly easy to just pull the good stuff right out. 

TW: So visually you can you can look at the spectagrams. So once you understand what you know the visual print of the sound is then you could scroll through things, but scrolling through things for a month’s worth of data is very daunting. So you can actually have an artificial intelligence training done on the sound itself, but also on the spectrogram. 

You can process this in the cloud when you get back here. This is also something done with ocean recording, where they’re able to put out ocean recorders for a month to listen to mammalian communication with pinnipeds or whales or any of those things. 

We really want to do this with long-term recordings for the pink river dolphins, but has the river goes up and down 20 to 30 feet every year we’re trying to figure out where we deploy those recorders that could be out there as a big hard drive, recording, and bring it back to the studio and and then going through it with AI or visually to see where we can find interesting things happening. 

JD: It sounds like we’re only beginning to understand what these ecosystems sound like and there’s so much more to discover.

TW: This is kind of the Golden Era right now for ecoacoustics. But conversely, Bernie Krause, who’s been recording since the 1970s and 80s, said that 85 percent of what he recorded has gone extinct already in terms of acoustic ecologies. So it’s changing everyday like we know is happening in our world and what we’re trying to catch up to is disappearing as fast as we’re getting new data.

JD: With that I think it’s a good time to climb to where we can hear better. 

[Sounds of howler monkeys and woodpeckers in the trees]

JD: Thank you Tim for sharing you working sounds with this over the last three episodes of the 60 second science podcast. And thank you to all the listeners for tuning in. We will have more experimental features like this in the podcast in the future. Until then, earphones on. 


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

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