Bio-Acoustic Habitat Theory
Audio download : http://audio.loe.org/audio/010803/010803bioacoustics.mp3
Scholarly articles on Bioacoustic habitat theory: https://scholar.google.com/scholar?q=bioacoustic+habitat+theory&hl=en&as_sdt=0&as_vis=1&oi=scholart&sa=X&ved=0ahUKEwi7u8OjuJ3TAhVW2GMKHbB_A6oQgQMIITAA
Extra source: http://blog.nature.org/science/explainer/how-can-bioacoustics-help-conserve-biodiversity/
According to scientists specializing in bio-acoustics, ecosystems have evolved a rich and complex sound quality. But noise pollution from cars, ships, and electronic devices is destroying these subtle, acoustic patterns in habitats around the globe. Reporter Nathan Johnson looks into the causes and consequences of the destruction of these natural soundscapes.Transcript
CURWOOD: According to a survey conducted by the National Park Service, one of the biggest draws of places like Yellowstone and Yosemite is the quiet one can find there. But these days, tranquility’s becoming more and more endangered. The snap of a twig or the whisper of the wind is often droned out by the whirring of cars and airplanes. Human activity is behind the loss of what are called natural soundscapes. People may feel this loss, but as reporter Nathan Johnson found out, the destruction of soundscapes is affecting other creatures as well.
[SOUND OF HIGHWAY TRAFFIC]
JOHNSON: It’s rush hour on the San Francisco Bay’s Richmond Bridge. A team of scientists are on a narrow observation deck, checking out a colony of harbor seals on some nearby rocks. These rocks are an important piece of real estate, according to biologist Emma Grigg.
GRIGG: You can look around and see that almost all the shoreline is developed to this point, so there’s not that many places for them to haul out in the bay. And in order for this population to persist in the bay, they need these haul-out areas.
JOHNSON: Scientists have seen how agitated the seals can get from all the noise around the bridge, so they’ve placed recording devices on the rocks and under the water, to monitor sound levels. But the seals do seem to have gotten used to most of the car and truck traffic.
GRIGG: They definitely will react if there’s any sound that goes above that sort of normal ambient level, like the screecher brakes or a siren going by; even horns. Or sometimes we’ll have workers who stop on the bridge and they’ll yell over the side. They’re able to discern that noise above other normal ambient noise, and will react to that.
JOHNSON: The fear is that a big construction project, scheduled to start up on the bridge any time, will scare these 200 seals away from this site. In this part of the bay it’s one of the only spots where they can rest after feeding for long stretches in the cold water. And scientists say that disturbances like this are becoming the norm. Christopher Clark is director of the Center for Bio-acoustics, at Cornell University.
CLARK: And there are many cases, in fact an alarmingly increasing number of cases, where human activities are creating in one sense an acoustic smog.
JOHNSON: For over two decades, Professor Clark has been studying the acoustics of the ocean, including the songs of large whales, like these Southern Right Whales he recorded off the coast of Argentina.
JOHNSON: Clark now does much of his research in the Mediterranean Sea.
CLARK: The Mediterranean Sea is a totally urbanized environment and it sounds, underwater, it sounds as though you were sort of lying under the street in downtown San Francisco. It’s just clogged with noise. And if you go to the Sea of Cortez, the Gulf of California, it’s quiet. You can hear the small panga boat of a fisherman come out of a harbor so far away you can’t even see it, and you can hear that little engine start up and change gear and move across the gulf. It’s just radically different between these two places.
JOHNSON: Relatively quiet places like the Sea of Cortez are heading towards extinction, according to Dr. Bernie Krause, a pioneer in the field of bio-acoustics. He says when he first started making recordings in nature, in 1968, he could get an hour of pristine sound for every fifteen hours of work.
KRAUSE: Now it takes me 2,000 hours to do the same thing. So I have to work, now, 2,000 hours in the field to get one hour of useable material. The reason is there’s so much noise around.
JOHNSON: Scientists don’t fully understand what this loss means, because there’s still so much that’s unknown about the way other creatures use and depend on sound to survive. However, for years, Dr. Krause has been documenting how sound can help gauge the health of a habitat. A breakthrough in his research came in Kenya, in 1983, at the end of a long day of recording.
KRAUSE: I was extremely tired, and I was lying there with my earphones on, hearing the sounds of the forest. And it occurred to me that they sounded like an orchestra. That it wasn’t a din of noise, it wasn’t a cacophony like we normally think of, but it was a wonderful animal orchestra.
JOHNSON: Krause returned to his lab, to create a spectrogram, a kind of graph allowing him to see what his microphones had recorded.
KRAUSE: When I looked at what I was hearing, everything was so well-defined. The insects were at one frequency. The frogs were at another frequency. The night birds were at a different frequency. The bats were yet another, showed it in another place in the spectrogram. Well, this was a revelation to me.
[NIGHT ANIMAL SOUNDS]
JOHNSON: If Krause’s theories are correct, a healthy habitat is one where animals have divided up the sound spectrum, much the way a radio dial is organized: different animals broadcasting at different frequencies. This helps members of each species hear each other, and it also helps them detect predators and prey.
To demonstrate this, Krause played a recording he made in the jungles of Borneo.
JOHNSON: So you’ll see this asian paradise flycatcher vocalizing in three niches. You’ll see a brown barbet immediately coming in to vocalize after the asian paradise flycatcher stops singing. And then you’ll see a ferruginous babbler, another bird, it comes in right after the brown barbet. So, it’s like something is conducting these voices out there.
JOHNSON: Krause says this habitat in Borneo doesn’t sound the same as when he recorded it 10 years ago, because of a new strip mine, upriver. And this points out the problem: namely, people show little sensitivity to the acoustic patterns evolution has worked out. Cornell University’s Chris Clark.
CLARK: Human activities make a lot of low frequency noise: trucks, trains, traffic, boats, engines–all that stuff. So there’s a lot of low frequency smog around. And we don’t know what the consequences of those impacts are, but in some cases, the potential consequences are fairly alarming.
JOHNSON: Some scientists say the navy’s new low frequency sonar can throw whales off their migration routes and even induce brain hemorrhages. And, in a study out of Montana State University, researchers established a link between snow mobile noise and increased enzyme stress levels in wolves and elk. But, short of turning off all our electronics and engines, no one’s really sure what to do.
MORTON: There’s a lot of underwater work that you’re not going to see. All the piers are going to get reinforced with new piles underwater…
JOHNSON: Back on the Richmond Bridge, Craig Morton, an environmental planner with California’s Department of Transportation, is explaining how workers are going to replace thousands of steel rivets with high strength bolts. He says the noise level from this operation will reach 90 to 95 decibels.
MORTON: A rock concert’s about 140; airport is probably 120; chain saw is probably 105. So it’s somewhere less than a chain saw.
JOHNSON: Even if the noise forces the seal colony to abandon this refuge, Chuck Morton says, realistically, there’s no way he can halt construction.
MORTON: We’ll talk to a contractor to see if there are any other construction techniques to reduce the noise levels, so we don’t have the impact as much. And that’s about all we can do.
JOHNSON: A movement is growing to reduce noise levels within the national park system. New rules, if they’re not gutted by the Bush administration, would phase out snow mobiles in Yellowstone. There’s also talk of new restrictions on noisy air flights over the Grand Canyon. Plus, the Park Service has directed its managers to treat soundscapes as a resource, meaning soundscapes can be protected just like any other resource, such as wildlife, water and clean air. For Living on Earth, this is Nathan Johnson, in San Francisco.