The sounds of the natural world will quickly fall silent and become ‘acoustic fossils’ without urgent action to halt environmental destruction, international experts warn.
As technology develops, sound has become an increasingly important way to measure the health and biodiversity of ecosystems: our forests, soils and oceans all produce their own acoustic signature. Scientists using ecoacoustics to measure habitats and species say thousands of habitats are silent as the planet witnesses extraordinary losses in the density and diversity of species. Together with them they disappear or lose volume: the morning cries of birds, the rustling of mammals through the thickets and the summer buzz of insects.
Today, tuning into some ecosystems reveals a “deadly silence”, says Prof. Steve Simpson of the University of Bristol. “It’s a race against time. We have only just discovered that they make such sounds, and yet we hear the sound disappear.”
“The changes are profound. And they happen everywhere,” says American soundscape recordist Bernie Krause, who has made more than 5,000 hours of recordings on seven continents over the past 55 years. He estimates that 70% of his archive comes from habitats that no longer exist.
Prof Bryan Pijanowski of Purdue University in the US has been listening to natural sounds and recording virtually all major ecosystem types in the world for forty years.
He said: “The sounds of the past that have been recorded and stored represent the sounds of species that may no longer be there – so that’s all we have. The recordings that many of us have [are] of places that no longer exist, and we don’t even know what species they are. In that sense they are already acoustic fossils.”
Numerous studies now document how natural soundscapes change, are disturbed and silenced. A 2021 study in the journal Nature of 200,000 sites in North America and Europe found that there has been “a pervasive loss of acoustic diversity and intensity of soundscapes on both continents over the past 25 years, driven by changes in species diversity and abundance.” The authors added: “One of the fundamental pathways through which humans interact with nature is in chronic decline, with potentially widespread consequences for human health and well-being.”
The shift in ecosystem sound is happening in the air, forests, soil and even underwater. During the Cold War, the US Navy used underwater surveillance systems to track Soviet submarines – and found they had difficulty doing so near coral reefs because of all the noise the reefs produced. It wasn’t until 1990 that civilian scientists were able to listen to this secret data.
“Every time we went to a healthy reef, it was astounding: the cacophony of sounds we heard,” says Simpson, who has been monitoring coral reefs using hydrophones for more than 20 years. “A healthy reef was a carnival of sound.”
At the start of his research, noise pollution from motorboats was his main concern, but in 2015 and 2016 there were significant bleaching events, resulting in 80% mortality of corals. “They cooked the reef,” he said. More than half of the world’s coral reef cover has been lost since 1950. If global warming reaches 2 degrees Celsius, more than 99% of coral reefs are expected to start dying.
The result of these bleaching events is a “deadly silence,” Simpson said. “We swam around those reefs and cried in our masks.”
“These sounds and silences speak to us as if in a mirror,” says Hildegard Westerkamp, a Canadian sound ecologist who has been capturing soundscapes for half a century, during which time wildlife populations have declined by almost 70% on average.
She began working on the World Soundscape Project in 1973 with the intention of documenting disappearing ecosystems. “We suggested that we listen to the soundscape, to everything, no matter how uncomfortable it may be – no matter how uncomfortable the message.”
She said: ‘The act of listening itself can be both comforting and deeply disturbing. But most importantly, it connects us to the reality of what we are dealing with.”
Good data is now being used alongside visual data as a way to monitor conservation efforts and ecosystem health. More advanced and cheaper recording equipment – as well as growing concerns about environmental destruction – are fueling the boom in eco-acoustic monitoring.
Related: Tell us how the sounds of nature are changing in your environment
As the sophistication of microphones has increased, scientists are using them to monitor life that would normally be inaudible to human ears. Marcus Maeder, an acoustic ecologist and sound artist from Switzerland, has been researching the sounds trees make under stress by pushing a microphone into the bark of a tree to listen to the living tissue. Stress sounds like pulses coming from the cavity, he said.
When he first pushed a microphone into the ground of a mountain meadow, he discovered that it was also full of noise, “a completely new kingdom of sounds.”
Intensively managed farmland, often doused with pesticides, sounds very different, Maeder said: “The soil becomes stagnant.”
For many researchers, disappearing soundscapes are both a source of sadness and of scientific interest. “It’s a sad thing to do, but it also helps me tell a story about the beauty of nature,” Pijanowski said. “As a scientist I have trouble explaining what biodiversity is, but when I play a recording and say what I’m talking about, these are the voices of this place. We can work to keep it or not.
“Sound is the most powerful trigger for emotions in humans. Acoustic memories are also very strong. I think about it as a scientist, but it’s hard not to be emotional.”
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