Ask most people about pollution and they will think of plastic, oil, smog, and chemicals. Ironically one of the biggest forms of pollution is one we do not hear about very often, noise pollution. Noise pollution, generally an unintended by-product of urbanisation, transport and industry, is a key characteristic of human development and population growth. With increasing levels of man-made noise in the environment, animals are having to contend more and more with external stimuli which can draw their attention away from key tasks. Human caused noise has consequences for wildlife, entire ecosystems and people. Unfortunately the animals cannot speak up for themselves, and so many must suffer.
Noise, by definition is an unwanted or inappropriate sound. The noise from aircraft, highways and many other industrial sources can be heard across the globe. It has become extremely difficult to find areas purely consisting of ‘the sound of nature’. Our loud lives matter as sound is crucial for many animals. Songs, grunts, roars or cheeps can be used to keep in contact with others, to warn of danger or defend territory, attract a mate or to beg for food from a parent. Humans are drowning out the necessary sounds of the wild.
We humans have gone from being relatively insignificant, quite hunter gathers to become extremely noisy neighbours. Traffic on American roads tripled, to almost 5 trillion vehicle kilometres per year, while air traffic also more than tripled between 1981 and 2007. The dramatic and comparatively recent rise in noise levels is marked in both magnitude and extent, with an estimated 30% of the European population exposed to road traffic noise levels greater than 55 decibels at night, well above the 40db target recommended by the World Health Organisation. It’s not just in our urban areas, remote natural areas do not escape anthropogenic noise. One study across 22 US national parks demonstrated that noise pollution was audible more than 28% of the time.
Furthermore, humans noise is not just irritating, it can have direct human health impacts. Chronic exposure to noise levels above 55db dramatically increases the risks of heart disease and stroke, while aircraft noise has been shown to impact the development of reading skills in children. This is not just the case for human health. Studies on Rhesus Monkeys show a 30% increase in blood pressure following exposure to 85db for 8 months. Another study showed that sound stressed mice became more susceptible to disease and less able to learn mazes when exposed to 82db for 8 hours a day. These laboratory studies show clear direct effects on animals, but what effects are there on wild animals in their natural environment?
Following on, almost all animal behaviours between individuals involve some form of vocal communication. The excessive amounts of anthropogenic noise means that many animal sounds are being drowned out and this is having detrimental effects on different behaviours. Firstly, the majority of animals use vocal signals in order to attract a member of the opposite sex. Loud human induced noise could be detrimental to the individual finding a reproductive partner. For example, male ovenbirds on quitter territories are more likely to have a mate than those on louder ones. For female grey tree frogs, increasing noise from nearby traffic has been shown to slow their abilities to listen for and locate male frogs that are calling during mating season. As for European tree frogs, they simply don’t call as much due to increasing noise pollution. Clearly both grey and European tree frogs have struggled to adapt their calls to the growing demands of increased environmental noise. By decreasing species ability to attract a mate, environmentalists say it could lead to less reproduction and declining populations of those species effected.
Perhaps a more devastating effect on the individual scale is the interruption human-noise has on predator-prey interactions. Every prey species on the planet depends on its ability to detect a predator for its survival. With increasing background noise, prey species are finding it harder to detect their match makers. For example, exposure of Desert Kangaroo Rats to dune buggy sounds (95db) caused a major reduction on detection distance from its predator the sidewinder (rattlesnake). In fact, the distance for the normal sand kicking response to the snakes presence was reduced from 40 cm to 2 cm, and it took three weeks for the rat to recover. This nocturnal rodent surely cannot survive for very long in such disadvantageous conditions. Anthropogenic noise masks auditory cues of the approaching threat and also tests the prey animals finite attention, effectively distracting it and preventing it from responding to predatory threats.
Moving on, the effects of anthropogenic noise are not just troubling terrestrial animals. In fact the problem of noise pollution is potentially worse for oceanic animals. There are two main reasons that make the impact of noise pollution in marine life especially grave. Firstly noise travels much more in water, covering greater distances than it would do on land. Secondly because the marine life is extremely sensitive to noise pollution due to their extreme reliance on underwater sounds for basic life functions like searching for food and mates and also avoiding predation. Under water we can now hear boats, ships and even aeroplanes. Large vessels in deep water can be detected tens of kilometres away. Perhaps the worst issue in the marine world is that of underwater resource exploration. Air guns used for marine oil and gas exploration are loud enough to affect animals up to 3 km away.
The effects of noise on marine animals are similar to those on us. If you’ve ever been left with ringing ears after a music concert, you’ll know that loud noise can temporarily affect your hearing or even damage it permanently. For fish, whales and other marine animals, intense underwater noises from blasts can cause acoustic trauma and even death. A range of cetaceans have displayed changes in behaviour. For example noise has been shown to reduce humpback whale communication, with less ‘song’ during periods of noise, even when the origin of the noise is 200 kilometres away. Both right and blue whales have been found to increase the level of vocalisations when exposed to sound sources in their vocal range. In effect, they need to ‘shout’ to allow themselves to be heard. It is not only the larger animals that are being affected. Squid and other cephalopods have also shown negative responses to noise pollution, disturbing the balance systems of squid, octopuses and cuttlefish. It would appear Jacques Cousteau’s silent world, is now very far away from being silent.
Moving on, the situation for many species looks extremely disturbing when it comes to noise pollution. However, some species are beginning to adapt to our noisy planet. For example, Nightingales have been found to raise the volume of their song in response to traffic noise and sing louder on weekday mornings than at weekends. Male song sparrows shift their song into higher frequencies, so it is not obscured by lower rumble of the cities. Meanwhile, black-chinned hummingbirds appear to actively select noisy areas near active gas wells to avoid nest predation by more disturbance sensitive species like jays. Although this may seem like a positive, the fact that some species are adapting and others aren’t is bad news. This can potentially alter whole food webs and species combinations, potentially effecting ecosystem function.
It is clear to see that the noise created by expanding human settlement is having detrimental effects on our natural world. So the question is, what are we going to do to help rectify the situation? The problematic noise is being generated by us and it is therefore up to us to find ways to reduce and stop it. Scientists are working to better understand where and how noise pollution is generated and where it is causing the most problems. Governments must start to enforce the use of quitter road surfaces, noise barriers, lowering speed limits, generating greener technologies such as quitter ships and machinery. Better planning can also reduce the issues, for example ‘quite zones’ for marine species in critical habitats and potentially creating laws that minimise noise pollution in bio-diversity hot-spots or sensitive habitats.
Scientists can help us better understand the issues and the problems these species are facing, governments will need to be active in passing legislation and funding better technologies, and the rest of us can take small steps to mitigate our own noise outputs. Personally having lived in Asia now for almost 3 years, I have become very frustrated with just how widespread the issue has become. It is now very rare to be able to enter a jungle and not hear the sound of a chainsaw or passing motorbike. It is now very rare to be able to snorkel or dive on a reef without the noise of speedboats passing overhead. The impact we have had on this planet is unthinkable. We use natural areas such as national parks for recreation, to relax and enjoy. Yet in our day to day lives we involve ourselves in its destruction. We can all adapt our lives in order to aid our natural world and we can all provide pressure on those who make the rules. We are destroying our natural world, and yet it is only us who can save it.