Turning down the volume: mitigating the impacts of anthropogenic noise pollution on animals and ecosystems

“We ought to call ourselves Homo clamorans. Noisemaking Man.” – Sir Terry Pratchett

It is no secret that we humans impact the world around us, from pumping out greenhouse gases, destroying swathes of rainforests, to emptying vast quantities of microplastics into the ocean. We do have the occasional positive impact too, of course. An often forgotten form of pollution is that of sensory pollution, including chemicals that interfere with animal signalling, artificial light at night, and noise pollution. The latter has been shown to impact ecosystems across the globe, including terrestrial, marine and freshwater systems, impacting a range of organisms via disruption to physiology, development and behaviour. Many animals rely on sounds and acoustic signals for communication, mating, detecting and avoiding predators, and for social interactions. Birdsong is not only uniquely beautiful to our own ears but is vital for mating and territory defence in many bird species, as well as having other potential social functions. We may listen to the calming sounds of whales to fall asleep to, but for the whales themselves their calls facilitate reproductive and foraging behaviours.  Even insects produce charmingly elaborate courtship songs, from grasshoppers to crickets to flies.

Infiltrating these natural soundscapes, anthropogenic noise pollution has become alarmingly ubiquitous. It has been recorded in both urban and rural environments and across all seven continents, despite a large geographical bias in research effort concentrated on Europe and North America. Sources of anthropogenic noise pollution include shipping noise, pile driving to support off-shore structures and seismic surveys, motorway traffic, and ambient urban noise from our cities. Noise pollution can impact organisms via several mechanistic pathways. One such pathway is masking; when a sound with an anthropogenic source occurs across the same frequency bands as a natural sound that an organism usually responds to, it can no longer detect and respond to the sound. This can result in an increased effort to produce the sound and altered behavioural responses by the receiver. Researchers in the US found that the acoustic courtship signals of the blacktail shiner (a common freshwater fish) were masked by traffic noise around bridge crossings. In France, it was discovered that the aggressive acoustic signals produced by male European lobsters vibrating their carapace were masked by shipping noise, resulting in the animals compensating by investing more time calling when anthropogenic noise was present. As well as masking, noise pollution can distract. Dwarf mongooses can become distracted by noise pollution caused by traffic, leading to lower engagement with olfactory cues of predators and consequent reduced vigilance and safety behaviours. It is clear therefore how such distraction could lead to increased predation for such animals. Finally, polluting anthropogenic sounds can also cause organisms to be misled, when they mistake the unnatural sound for something meaningful. Examples come from beaked whales, which exhibit behavioural changes in response to underwater sonar signals; when they detect the calls of killer whales (predators of beaked whales) they ascend more slowly from foraging dives, and this is also the case in response to the sonar signal.

There are potentially even more damaging mechanisms at play when it comes to noise pollution and its effects on organisms. As well as causing behavioural changes through masking, distraction or misleading, anthropogenic noise can have direct physical impacts on the structures that animals have evolved to detect acoustic stimuli, as well as on their development and physiology. Sea hare larvae development and survival is impaired by exposure to boat noise, with a 22% elevated risk of mortality as a result of anthropogenic noise pollution.  Impulsive sound exposure causes massive acoustic trauma to the sensory epithelium of the sound-detecting structures of jellyfish, and extreme cases of exposure can lead to membrane damage and cell death. Additionally, an increase in stress hormone circulation as a result of exposure to noise pollution can lead to altered behaviour, ultimately impacting ecological processes on a larger scale. The story gets more complicated when we consider that noise pollution often co-occurs with other forms of anthropogenic pollution or disturbance, including light pollution, which can have complex and cross-modal effects on behaviours.

As well as the clear impacts on animal behaviour, physiology and ecology, noise pollution also has a demonstrable impact on human health. A recent review highlighted that chronic exposure to noise pollution can be a major contributor to mental health conditions, cardiovascular disease, sleep disturbances and stroke mortality. Perhaps unsurprisingly, there is evidence of socioeconomic and ethnic health inequalities relating to noise exposure in Europe, Asia, and the US, meaning that reducing noise pollution globally is not just important for wildlife conservation and ecosystem health, but also for human health and social justice.

So, what can we do about this problem? What are the solutions short of ceasing the majority of human activities? On an individual scale, making sure our own activities are not contributing to local noise and other sensory pollution is a good place to start. Although we often think about whales swimming in the distant ocean or birds and mammals trying to be heard across huge natural areas criss-crossed with roads, the birds, small mammals and insects in our own gardens and parks, and the fish and crabs along our shorelines are equally as affected by noise pollution. On a larger scale, it is easy to feel helpless. Researchers continue to investigate the mechanisms and ecological effects underlying sensory pollution and the disruption it can cause, and in doing so, highlight the need for noise pollution to be considered within sustainable development goals, conservation efforts, and public health. But the rest of us can do our part as well. Major sources of noise pollution in our modern world are oil and gas fields and gargantuan data centres like the ones currently being proposed here in Scotland. By speaking out, signing petitions, writing to our MSPs, and opposing the continuing development of such sites, we can have a positive impact on reducing noise pollution for ourselves and the other animals we share our world with.