No More Silent Springs: How Anthropogenic Noise Pollution Impacts Organisms
Holly A. Connop
8 min read
Anthropogenic noise, like many pollutants, is an often-invisible danger on the rise due to urbanization (Tong & Kang, 2020). Studies have observed adverse impacts on species from numerous kingdoms, including birds; aquatic mammals; non-aquatic mammals, such as bats; frogs; insects such as crickets; and even plants. The first category of this paper discusses noise pollution’s effects on communication abilities and, in turn, mating opportunities. In a second category, navigation and foraging are affected, altering basic survival means. Last, this review discusses direct impacts of noise pollution on the physiological health of organisms.
Communication and Mating
Many animals use calls to find mates. An example of how noise pollution impedes this process was observed in the Hyla arborea frog species (Lengagne, 2008). Researchers determined that when traffic noise was played at 72 dB, the calling effort of male frogs decreased by 29%; at 88 dB, calling effort decreased by 50%. Lengagne predicted this to reduce reproductive potential, as female frogs may struggle to choose a mate. Similar effects were found in Bornean tree frogs (Yi & Sheridan, 2019), and data on impaired mate selection has been shown in female wood frogs exposed to noise as well (Tennessen et al., 2014). This is concerning because, according to the United States Geological Survey, frog populations are declining by 3.79% per year — a rate that could result in some populations being halved in just 20 years (USGS, 2016). The decline has already been documented for at least three decades in the Americas, Europe, and Australia, with Asia and Africa not listed only because these continents were not being sufficiently researched at the time (Down to Earth, 1991). Given the findings on reduced mating ability during noise exposure, urban noise may be one of many plausible anthropogenic contributors to globally declining amphibian populations in recent years.
Tree swallows have also been shown to experience reduced reproductive success in the presence of vehicle noise (Injaian et al., 2018). According to Injaian’s study, birds in the treatment group, who were exposed to loud traffic sounds, produced nestlings with increased oxidative stress and decreased bodily size. The authors also proposed that inhibited communication between offspring and parents may account for the difference. Consequently, nestlings took ~1.5 days longer to leave the nest. Injaian et al. argued that while these outcomes may not immediately threaten tree swallow populations, birds with higher oxidative stress and decreased body size are more likely to die prematurely, as are nestlings who stay in the nest longer, exposed to predators (Injaian et al., 2018).
One bizarre finding: the reproductive system of male crickets also reacts to excessive noise. Researchers discovered reductions in the size of a structure called the spermatophore mold, whose function is to transmit sperm cells effectively (Bowen et al., 2020). This may be attributed to noise causing a stress response, as seen in the tree swallows with elevated oxidative stress. Further study is needed to determine the full implications of shrinkages like this.
Foraging and Navigation
Nocturnal animals commonly depend on sound to find food. In a study on desert bats in Israel, experimenters played loud music (between 20-40 kHz) near a remote waterbody (Domer et al., 2021). Domer et al. discovered that the louder the music, the less successful the bats’ drinking attempts were. Another type of bat, the Eurasian Daubenton’s bat, also has difficulty using echolocation to detect prey in noisy conditions, resulting in decreased foraging success (Luo et al., 2015). Luo et al. concluded that noise aversion was the main cause, as opposed to reduced attention or acoustic masking. Airport noise can also impede proper foraging in a third bat type, known as the Japanese house or pipistrelle bat, due to noise avoidance (Wang et al., 2022).
In owls, Bachman (2010) notes that noise pollution reduces foraging ability because the rustlings and squeaks of mice are easily masked by urban sounds; the predator (in this case, barn owls) must slow down to hear their prey (Bachmann, 2010). Urban areas also drive tawny owls into neighbouring forests (Frōhlich & Ciach, 2017), but of course, the birds can only do this when there are forests to migrate to. Forest protection, and the protection of natural habitats in general, are clearly crucial in reducing the impacts of urbanization and noise on these creatures.
Perhaps the most compelling (and disturbing) aspect of noise pollution is its impact on the physiology of organisms. In marine mammals, the effects are well documented. Like birds and bats, cetaceans exposed to vessel traffic have been found to have issues with communication, echolocation, and foraging (Gordon, 2018). Compounding this, however, is that these mammals demonstrate extreme stress responses: whale-watching ships emitting low-frequency noise (20-200 Hz) in the Bay of Fundy were associated with elevated levels of stress hormones called glucocorticoids (GCs) in endangered North Atlantic right whales (Rolland et al., 2012). According to Rolland’s data, the levels decreased drastically after September 2001, the same time that 9/11 prompted intense restrictions on maritime transport (OECD, 2003). Given New York’s proximity to the North Atlantic, reduced ship traffic resulting from 9/11 aftermath is a probable explanation for the decrease. Similar stress effects were found in dolphins (Yang et al., 2021). In addition, a group of 13 Arctic narwhals studied for five years were found to have increased stroke rates and diving effort when exposed to airgun noise and seismic ship traffic (Williams et al., 2022). Surprisingly, greater diving effort led to severe bradycardia (low heartbeat) over time. This finding suggests that fear responses resulting from noise cause considerable deviations from healthy homeostasis in narwhals. Given that marine mammals are becoming extinct rapidly in relation to land animals — chiefly due to anthropogenic causes! — every threat to their wellbeing should be of concern to environmentalists (Nunez, 2019).
In terrestrial mammals, other studies on glucocorticoids have been conducted. An article initially focused on grouse also discusses the correlation between higher vehicle traffic and increased GCs in wolf and elk feces (Blickley et al., 2012). Blickley’s article states that human children living near busy roads have heightened GC levels in their urine, which the authors say is associated with sleep disruptions and cognitive problems. Furthermore, there is a positive relationship between noise and various stress-related human diseases (Basner et al., 2014; see Figure 1). Noise-induced stress, like any other stress, has been shown to have serious impacts on the health of organisms. This evidence that noise can induce observable stress responses and stress-related diseases even in relatively large mammals such as humans is highly alarming because of the many known health effects of stress and its death toll. It has been estimated that 180,000 people in the UK die due to stress-related illness each year (Salleh, 2008). This is more than double the deaths attributed annually to smoking in the UK (NHS, 2018). Small animals are often more vulnerable — according to Animal Ethics (2019) even the sounds of a predatory cat can cause fatal heart attacks in rats, let alone the mechanical noise humans create. In terms of animal health, stress may be the most threatening consequence of anthropogenic noise.
Fascinatingly, plant physiology is also affected by noise, but in contradictory ways. Some advocate for using vegetation to minimize noise pollution, but this may have implications for plant health as well. For example, pinyon and juniper trees face reduced seed propagation even after the noise source is removed (Phillips et al., 2021). This may be explained by dispersers (birds) practicing noise avoidance, as discussed with the tawny owls seeking silence in forests (Frōhlich & Ciach, 2017). Conversely, a few pollinators such as hummingbirds exhibit positive responses, seemingly motivated by certain kinds of noise exposure (Francis et al., 2012). More research is essential to uncover how certain types of noise and volume ranges may affect species interactions and the health of plants.
Noise pollution may not be immediately visible, but its impacts become increasingly so. As urbanization conquers the globe, noise created by vehicles and other manmade machinery continues to disturb the normal behaviours and physiological processes of fauna and flora. The effects are widespread, and in the long term, may threaten to put many species at risk. Similar effects of noise pollution can be seen across several species: communication is notably impaired in birds, frogs, crickets, and cetaceans, reducing reproductive potential; diminished foraging and navigational abilities have been observed in birds, bats, and cetaceans, threatening the livelihoods of these animals; and lastly, direct stress-related health impacts including increased respiration, heart abnormalities, oxidative stress, and/or elevated glucocorticoids have been observed in narwhals, tree swallows, and land mammals, including humans. Fleeing behaviour associated with anxiety was also common in bats, whales, and seed-dispersing birds. The literature suggests that when stress responses are coupled with noise avoidance, the effects on the health of species are particularly detrimental. While vegetation can be used to mitigate noise, some plants and their pollinators are harmed by noise pollution in the meanwhile. Other mitigation strategies that may prove useful considering the literature include preserving natural habitats free of noise (e.g. forests), reducing the noise volume that machines produce, or limiting noise when noise-avoidant species are active and attempting to feed.
It is critical that humankind develops mitigation tactics and tools against urban noise to live in harmony with fellow animals — after all, the effects of uncontrolled noise pollution may cause ecosystem disturbances that could, one day, climb up the food chain.
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