Among the different forms of pollution , the one considered most relevant is that related to chemical substances. Much has been said about atmospheric pollutants that cause a greenhouse effect that triggers climate change on a global scale; of toxic spills on the ground that end up infiltrating aquifers, terrestrial wetlands and the sea, negatively affecting ecosystems; or from solid products that do not degrade and end up deposited, accumulating in the oceans, such as microplastics.
But not all existing pollution is chemical . We should also talk about physical pollution, such as light pollution —excess artificial light at night—, which affects animals, plants and those who are dedicated to observing astronomy, or noise pollution . This article will deal with this type of contamination.
The noises that nature does not know
The noise generated by human activity comes from a wide variety of sources , the majority from transport. Road traffic on highways and other thoroughfares, the thunderous passage of a high-speed train, the roaring engine of an airplane or the constant and monotonous engines of ships, many of which also incorporate sonar – a system for detecting objects under water through the use of sound pulses—all of which generate a great deal of noise.
But they are not the only sources of anthropogenic sound. The industry, the agricultural machinery, or, simply, the agglomeration of people can cause sounds that generate impacts on wildlife. Also included in this category are the noises caused by some invasive exotic species, since, after all, the human being has been responsible for their presence.
In order to know how noise impacts living beings, it is first important to know how the intensity of a sound is measured . Decibels (dB) measure the strength of sound based on a given area.
The decibel is a magnitude that, like luminosity, is reduced with the square of the distance, that is, the loss of force that occurs when moving away from the source from one meter to two is the same as that which occurs when moving away from the source. two to four, and four to eight. On the other hand, the decibel scale is not linear, like meters, but logarithmic in base 10. This means that an object that emits a sound of 20 dB is not emitting twice as much as another object that emits 10 dB, but ten times more .
It is considered that with sounds of approximately 40 dB wildlife already generates responses, and significant impacts occur with noises of 50 dB .
Alterations in the dynamics of predation
In general, there are two types of noise that affect living beings: intermittent or unpredictable sound , perceived as a threat signal, and chronic noise , which generates constant interference.
Specific, unpredictable or random noises activate the alert position in animals , increasing the level of vigilance and consequently reducing the time spent searching for food. In addition, these intermittent noises can interfere with the dynamics of predators and prey. A punctual sound can put prey on alert and cause a predator to miss its chance to hunt it, or even startle the predator and give itself away prematurely.
On the contrary, chronic and constant noise can interfere with animals that rely more on the sense of hearing , because they acclimatize to constant sound and lose hearing acuity to perceive sound details.
In animals that hunt by ear, such as bats, such interference has been shown to hamper their hunting abilities, increase the time they spend hunting and reduce their success. Animals that use sound to communicate, such as cetaceans, may have difficulty doing so because of the noise of boat engines. Also prey, due to the background noise, have difficulty hearing the approaching predator, and become victims of an encounter that, in the absence of noise, could have a different outcome.
Alterations of temporal patterns
Noises that are perceived as threatening can also cause certain changes in temporary behavior patterns . For example, it has been observed that foxes tend to cross roads when there is less traffic noise, changing the time of day they move. Manatees also undergo these types of changes; maritime traffic tends to interrupt feeding times .
Among birds, a change in the hours at which they sing has been observed. Urban robins prefer to wait at night, when city noise is much less. Changes in the time of song emission of less than an hour can break the coordination between the sender and the receiver of the song . If that coordination is disrupted between singing males and responding females, there will be a huge impact on reproductive success.
Of course, the time of sleep is also an important factor. The sleep-wake cycles of animals are related to light, but the presence of noise during the time when the animal should be sleeping interrupts its sleep and alters these cycles. Although this phenomenon is widely studied in humans, there is very little scientific information on the impact of sleep disruption in non-human animals. But it is obvious that it will have detrimental effects.
Distribution changes
Generally, moving from a noisy area to a quieter one has been considered as a form of defense against the impacts of noise pollution. However, in reality, it is still another impact mode in itself.
Animals may leave certain areas when frequent or chronic noises interfere with signal detection or when more variable sounds are perceived as threatening. In addition, many species use their hearing to choose places to rest, to feed —such as some bats— and even to find a place to reproduce —such as some frogs and newts—, and the presence of noise can affect these behaviors, causing them to seek other places .
These changes in species distribution may have subsequent ecological effects . The disappearance of animals from an ecosystem due to noise or their entry into a silent ecosystem are events that destabilize the ecological dynamics of both places. It has been observed that some species of capercaillie during the breeding season are inhibited by the presence of specific unpredictable noises, such as a car on a secondary road, which can affect the survival of the species .
And an added problem, related to distribution, appears when it comes to censusing the animals. When noises occur, birds remain in their roosts longer, reducing the number of birds a researcher can identify, significantly biasing the measurement of site occupancy and abundance.
REFERENCES:Â
Blickley 1, J. L. et al. 2010. Impacts of Anthropogenic Noise on Wildlife: Research Priorities for the Development of Standards and Mitigation. Journal of International Wildlife Law & Policy, 13(4), 274-292. DOI: 10.1080/13880292.2010.524564
Francis, C. D. et al. 2013. A framework for understanding noise impacts on wildlife: an urgent conservation priority. Frontiers in Ecology and the Environment, 11(6), 305-313. DOI: 10.1890/120183
Pater, L. L. et al. 2009. Recommendations for Improved Assessment of Noise Impacts on Wildlife. The Journal of Wildlife Management, 73(5), 788-795. DOI: 10.2193/2006-235
Shannon, G. et al. 2016. A synthesis of two decades of research documenting the effects of noise on wildlife. Biological Reviews, 91(4), 982-1005. DOI: 10.1111/brv.12207
