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Effects of natural noise pollution on animals similar to noise from humans

Researchers used solar-powered speakers to play whitewater noise at high volumes near mountain streams in Idaho, which led their finding that natural noise can be as disruptive as human-caused noise. Photo by Cory Toth/Boise State
Researchers used solar-powered speakers to play whitewater noise at high volumes near mountain streams in Idaho, which led their finding that natural noise can be as disruptive as human-caused noise. Photo by Cory Toth/Boise State

May 24 (UPI) -- Loud noises, whether from big boat engines or freeway traffic, can disrupt the communication and navigation abilities of many animals -- and they are known to alter their movement and feeding patterns to avoid noise pollution.

But what about the sounds of nature?

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It turns out natural noise, like the rumble of thunder or the roar of a waterfall, can also influence the behavior of nearby wildlife, according to a study published Monday in the journal Nature Communications.

When researchers at Boise State University pumped whitewater noise into a forest at significant decibels, they found birds stopped feeding nearby, while bats altered their foraging strategies.

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"Naturally-loud environments have been largely neglected in ecological research," first author Dylan Gomes, a recent doctoral graduate of Boise State, said in a press release.

"We aimed to test the hypothesis that intense natural noise can shape animal distributions and behavior by experimentally broadcasting whitewater river noise at a massive scale," Gomes said.

At some 60 location in Idaho's Pioneer Mountains, scientists set up solar-powered speakers next to small alpine streams. The research team pumped in both realistic river sounds and whitewater recordings that had been shifted upwards in frequency.

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"The prevailing hypothesis for why many animals avoid noise is called masking. Masking occurs when noise overlaps in frequency -- what we perceive as pitch -- with a biological signal or cue," senior study author Jesse Barber said in a press release.

"By broadcasting noise of different frequencies, we hoped to assess the role that masking of important sounds, such as birdsong, plays in the avoidance of noisy places," said Barber, an associate professor of biology at Boise State.

To quantify foraging patterns, researchers scattered hundreds of faux caterpillars among the test sites. By examining the markings left on and around the clay caterpillars, researchers were able to estimate the levels of foraging activity at each site.

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The data showed sound frequency overlap best predicted the the absence of birds at moderate noise levels. Once the whitewater noise crossed a certain decibel threshold, becoming about as loud as a busy freeway, the test sites proved equally unfriendly to hungry birds.

To measure bat feeding patterns, scientists deployed a "robo-moth" to replicate the wingbeats of insects that bats like to snatch from the sky. Researchers also played a recording of different insects sounds -- insects walking across leaves, as well cricket and katydid calls.

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When the river noises were quiet enough, bats responded to the mixtape of insect sounds, but as the decibels increased, bats began relying exclusively on echolocation and were more likely to react to the robo-moth.

"Our work showing that natural noise can structure where animals live and how they behave only increases the call to manage human-caused noise," said Clinton Francis, co-principal investigator and researcher at California Polytechnic State University.

"The spatial and temporal footprint of anthropogenic noise is far greater than loud natural environments," said Francis, co-principal investigator and researcher at California Polytechnic State University.

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