What the science of sound tells us about the world

Environmental sounds, from chirping birds to rustling trees, can tell humans a lot about the world -- if they listen. A researcher wants to create a scientific field devoted to the ecological importance of sounds.

Environmental sounds, from chirping birds to rustling trees, can tell humans a lot about the world -- if they listen. So says Bryan Pijanowski, an associate professor of forestry and natural resources at Purdue University.

Pijanowski is championing an effort to create a field of science to study the ecological importance of sounds. We spoke yesterday about how this effort could help us monitor the effects of climate change, including the "acoustic fossils" that are left behind.

You're working in the field of soundscape ecology, using sound to understand the ecological characteristics of landscapes. Why is this important?

Up to now, we've had a lot of great science in the area of bio-acoustics and environmental acoustics. Bio-acoustics has been the study of the vocalization of animals, studying behavior, physiology, anatomy related to that. We've had a lot of research done on environmental acoustics, looking at how noise propagates through the landscape. In working with issues dealing with climate change and land use and biodiversity, we realized we needed measures that allowed us to incorporate all of those aspects into something that was unifying.

Acoustics seems to be it. It allows us to measure the biodiversity that occurs in a habitat. But also -- because humans make noise -- we can use noise as a surrogate of human activities. The terms we've developed allow us to think through ecosystem processes and the way humans impact that. The terms we've developed are:

  • Biophony - To be able to understand the biological voices that occur in the landscape
  • Geophony - [Sounds from the geophysical environment], such as wind and water
  • Anthrophony - The noise that humans make, which can be produced by a variety of instruments

If you put a microphone in the middle of an environment, you can record all those. You can record them for long periods of time. You can look at all aspects of the environment at any time of the day.

How can sound help us monitor climate change?

Let me give you an example. Some of the studies we're conducting are in the tropics. Whenever you're walking around in the tropical forests, there are lots of streams. Those streams are rushing and gushing right after a rainfall. They're creating a lot of sounds. The organisms that exist in that landscape have to compete with those sounds. They had to evolve their vocalization, so they can pierce above those background sounds. I've been through those same streams when it's been very dry and it's quiet. So climate has a huge effect on certain kinds of landscapes. There are some organisms that exist in quiet landscapes. They have fairly soft voices. But if climate were to change -- if it became windier or there was a lot of rain -- that could impact their vocalizations, which could impact their life history and reproduction. Sound can be a universal measure and help us to understand all these global environmental change issues.

You've monitored sound in the tropics, but also near the Purdue campus. Talk about your work capturing sounds that are in danger of being lost.

It's really at the heart of some of the early results of this new field. In habitats where there is lots of natural vegetation, there are many organisms making vocalizations. As you look at areas that are more disturbed, there are few biological vocalizations occurring. There are fewer organisms that are singing and calling and chirping. As we continue to modify a habitat, we're in danger of losing the biological signals that we're all used to in the landscape. We're in danger of silencing the landscape. That's why we hearken back to Rachel Carson's original statements that by modifying the landscape we could be pushing out organisms that are creating the biological voices of that landscape. We're also in danger of replacing it with the anthrophony, as well.

As humans continue to disconnect from nature -- because we're more and more an urban species -- we're losing the acoustic link to nature. In many cases, we've lost the visual one. But losing the acoustic one is very important. We've lost the ability to listen because as we walk around the urban environment, we've learned to turn off our ears. We no longer listen to the birds or other critters.

What are we missing when we don't hear these natural sounds?

The monitoring techniques we're developing can be early warning tools to allow us to say: 'These landscapes are now silent. There's something going on here that might not be good.' If we have these out in the environment, we can use them as rapid assessment tools to assess the biodiversity or whether key species exist in a landscape.

Some soundscape recordings are available online. Talk about what we hear in a few of them.

Urban noise taken at a busy intersection in Tippecanoe County near Purdue University: You have biophony and anthrophony there. If you listen very carefully, you can probably hear a little bit of wind. This is a landscape we're all used to listening to. It would be very typical of the Midwest. I also chose it because we have night hawks flying overhead. They're a key species that makes sounds at night in Midwestern urban areas. There's a lot of activity. There are bells and whistles and horns and brakes. We're trying to analyze this kind of information in urban environments and natural environments. How do they differ?

Ambient sounds in the Algonquin National Park in Ontario, Canada, are quickly replaced by the howls of gray wolves: It's one of my favorite recordings because of the way in which the sounds evolve over time. It starts off very quiet. You only have a few birds singing. But you hear something in the background and you can't quite detect what it is. It takes a few seconds before you realize what you're listening to. The sounds are very beautiful, but eerie. They send certain kinds of emotions through to humans that we've associated with certain kinds of landscapes. In this case, we have sounds that create a visual of what this landscape looks like.

Nighttime recording of forest elephants trumpeting around a bai: This is taken at the middle of the night. You have crickets and frogs, but they're vocalizing at a low frequency. This is a unique soundscape. It's probably one of the only ones in the world that sound like this. You have a salt marsh where the elephants come and use it as part of their diet. Surrounding it are rock outcrops. They're using their vocalizations in the rock outcrops to propagate, to make it much more three-dimensional. The structure of the landscape and the unique resource being used by the elephants create a one-of-a-kind soundscape. We need to think about how to preserve the landscape around [the elephant], so the sounds can be propagated in a way that helps promote the animal.

Will you return to these locations to record how the soundscapes evolve?

I'm trying to find funding to do that. I've collaborated with Bernie Krause, who made many of these recordings. He recorded many of these in the 1980s and '90s. The sad part is that some of the recordings -- I would say 40 to 50 percent -- we can't go back to because they no longer exist. They're no longer natural. They've been converted to crop or into an urban area. Those soundscapes have been lost forever. These become kind of acoustic fossils. In many respects, they're all we have that represent that landscape and what existed there. A lot of the research we're trying to do is very new. We don't know how to process a lot of the data. But we're recording it anyway because we know these are important records. We're capturing the digital representation of the soundscape.

What's the next step in your work?

I'm trying to think about conservation efforts. How do we use these new technologies to help conservation efforts, especially in the tropics and the temperate forests? We have some plans to go to Costa Rica and Italy to show conservation groups how we're going out in the field recording natural sounds and using that to come up with measures of biodiversity.

Is there anything else you'd like to add?

I'd encourage people to take a sound walk. You go out and just listen. Try to get away from an urban environment. If you take a hike, listen to everything that's around you. Try to listen to the wind. Listen to the birds. Listen to the water, if you have a stream nearby. Try to observe things that you've never listened to before. That would get you thinking more along the lines that I have been thinking -- that there's a lot we've been missing as a society and a community of scientists.

Photo: From right, Luis J. Villanueva-Rivera, Bryan Pijanowski and Sarah Dumyahn collect data from a remote listening post that records sounds from the surrounding area / Courtesy of Purdue Agricultural Communication and Tom Campbell

This post was originally published on Smartplanet.com