Noise pollution is reshaping the health and behaviour of animals everywhere

If you listen closely to an underwater seagrass meadow, you can hear the actual sound of photosynthesis. During the day, tiny bubbles of oxygen float from the blades of the seagrass to the ocean’s surface. The popping sound these bubbles make when they burst is like “tinkling bells”, according to Carlos Duarte, a keen scuba diver and expert on ocean noise at the King Abdullah University of Science and Technology in Saudi Arabia.

“As long as the meadows are more than 2 metres beneath the ocean surface, when the bubbles break they generate a vibration that is in the same sound frequency as bells,” he says. “If you have a hydrophone and you quantify this, then you could even calculate photosynthetic rates.”

But most of the time, this remarkable acoustic phenomenon is drowned out by human-caused noise pollution. There is barely a habitat on Earth that isn’t subjected to anthropogenic noise pollution from boats, cars, aeroplanes or any number of other noisy human activities. In the oceans, ambient noise levels are about 10 times higher than they were in 1950. “To understand the impact of noise on the marine environment, we need to imagine ourselves living in a great party, 24/7, throughout our entire lifespan. It is really a persistent and chronic impact,” says Duarte.

Now, scientists are learning more about how serious and widespread the impact of noise pollution is on wildlife subjected to it – and the results are disturbing. A meta-analysis published in the journal Science earlier this month looked at 214 experimental studies on 177 aquatic and terrestrial species, spanning six continents. It concluded that noise pollution altered at least one physiological, developmental or behavioural trait in 80 per cent of the species studied, with the effects occurring in every habitat. In short, noise pollution is reshaping the health and behaviour of a huge range of animals across land and sea.

“Every ecosystem, or every major habitat, is affected by noise,” says Hansjoerg Kunc at Queen’s University Belfast in the UK, who conducted the analysis with his colleague Rouven Schmidt. “We looked at a lot of different physiological responses [in wildlife] and basically nearly all of them found an effect for noise.”

In general, noise forces predators to work 2.5 times harder to catch 25 per cent less prey overall, reported Kunc and Schmidt. Creatures like bats expend more energy and are less successful at hunting when subjected to ambient noise, while noise from ship engines disrupts communication and disorientates marine life such as whales and dolphins.

Animals also learn to avoid noisy habitats, which shrinks their available area and therefore limits their population size. Dolphins, for example, actively avoid noisy coastlines, while bats have been shown to avoid roads that were noisy during a motorcycle rally long after the vehicles had left the area.

In noise-polluted areas, mortality among animals studied jumped by 138 per cent, on average. Sometimes, the death is instantaneous: underwater explosions from oil and gas exploration, for example, can cause a fish’s bladder to explode. Other times, it is slower and more painful, such as gradual starvation from reduced hunting success.

Not every animal suffers a negative impact from noise pollution, Kunc notes. Some predators might benefit from noise – enjoying increased hunting success when human noise flushes their prey out of its hiding place, for example.

But even though some animals might benefit in the short term, the overall effect is negative on the ecosystem, he says, because its natural dynamics are being warped by external stress. “If you think about an ecosystem, all species in this ecosystem have adapted to the way it should be,” he says. “So, from my point of view, it doesn’t really matter who is more affected or less affected. It is changing, and that is what we want to avoid, because we want to protect a functioning ecosystem.”

Kunc wants more thought to be given to protecting the soundscape of the natural world, alongside the conservation of physical habitats. “We know that the acoustic environment is a strong evolutionary force, and we have shown that it really changes the physiology, development and behaviour [of wildlife],” he says.

Some efforts are already under way. In the US, national parks such as Yellowstone have designated quiet zones, which reduce the amount of noise made by visitors by 3 to 5 decibels according to Rachel Buxton, formerly of the US National Parks Service and now at Carleton University in Canada.

She thinks more can be done to reduce noise pollution, especially in protected areas, such as by closing roads to traffic during certain periods or re-routing aircraft to shadow busy road networks and avoid wilderness areas.

“Think of the Grand Canyon. We wouldn’t dream of building a giant building in the middle of the Grand Canyon, and yet there are overflight tours that pass over the airspace all the time, polluting the whole space with noise,” she points out.

We also need to tackle noise pollution at sea, says Duarte. He argues for enforcing acoustic limits in marine protected areas, which could include setting noise limits for ships and other marine activities.

New technologies also give hope for a quieter future. Emerging evidence suggests that electric vehicles are quieter and therefore less disturbing to most wildlife. Similarly, electric motorboats and ferries could lead to quieter shorelines for marine life, says Duarte. “Moving to electric mobility, which we’ve done largely on land, to the ocean will immediately reduce noise around the shorelines,” he says, pointing out that countries such as Sweden are leading the way in creating a market for electric boats.

The covid-19 pandemic offers an insight into what happens in the natural world when the noise stops. Noise pollution across oceans dropped by 20 per cent during the crisis, says Duarte, and led to extraordinary sightings of marine life returning to busy waterways and city shorelines, and the sound of birdsong filling cities.

Unlike pollutants that linger in the atmosphere, shutting off the noise immediately removes the problem, Duarte points out. “As soon as the noise stops, then animals claim back their ancestral territory and home,” he says.