Sensory Pollution and Functional Fragmentation: Sounding the Alarm on Noise
July 31, 2026
I have a confession: I grimace whenever I see images of wildlife crossings over multi-lane motorways. The structure enables animals to avoid a deadly physical barrier, and that is progress. Nonetheless, I cannot help but think about the additional ecological damage caused by such volumes of traffic. And, yes, a pun is intended when I mention “volumes of traffic,” for I am thinking primarily about noise. A transition to electric vehicles would reduce emissions, but its ability to mitigate noise pollution is limited. At freeway speeds, tire noise is the main component of the rumble of traffic.
Wildlife crossing in Canada’s Banff National Park, photo by Coolcaesar / Wikimedia, CC BY-SA 4.0
In their recent “Manifesto for multidimensional ecological networks,” engineer Romain Sordello and coauthors note that “a road is not only a physical issue […] but also a multi-sensory polluting infrastructure.” Sordello and coauthors call attention to several sensory pollutants, including roadway light pollution, another significant concern that LED headlights are now exacerbating. Ruskin Hartley, DarkSky International’s CEO and executive director, illuminated the issue of light pollution in a Rewilding Earth podcast. In this article, I want to sound the alarm about noise.
Numerous studies have found that traffic noise is detrimental to wildlife. A new meta-analysis of research on 160 bird species concludes that “noise significantly impacts communication risk behaviours, foraging, aggression, and physiology and [has] a strong effect on habitat use and a negative impact on reproduction.”
Eagle owl on the hunt, photo by Leo Reynolds, CC BY-NC-SA 2.0
Traffic noise both masks cues that predators like owls and mouse-eared bats use for hunting and masks alarm calls that prey animals use to warn of predators. By altering predator-prey dynamics, road noise might have cascading ecological effects.
Wildlife biologist Amy Collins and colleagues examined noise-influenced predator-prey relationships near wildlife crossing structures in California. They found that coyotes avoided areas with chronic traffic noise, while mule deer continued to browse. Indeed, mule deer displayed less anti-predator behavior near busy roads, apparently using traffic noise as a “shield” to protect them from predators. Thus, although wildlife crossings provided physical connectivity, roadways continued to disrupt the “landscapes of fear” in their vicinity. Moreover, Collins and coauthors found that acute traffic noise provoked startle responses in both coyotes and mule deer, deterring them from using the crossings.
White-crowned sparrow, photo by Kate McFarland
Noise pollution also impedes vocal communication for numerous species of birds and frogs, sometimes causing these animals to alter their vocalizations to make themselves heard above the low-frequency rumble of traffic, even though the altered calls might be less effective in attracting mates. A study conducted during the COVID-19 pandemic found that white-crowned sparrows reverted to songs with lower notes when urban-dwelling humans were under lockdown. Evidently, the birds favored these songs when not forced to compete with traffic noise. Furthermore, traffic noise has been shown to retard vocal learning in songbirds, in addition to hindering cognitive performance in other domains.
Traffic noise can also have direct physiological effects on organisms, such as impairing the growth of baby songbirds. Negative physiological effects aren’t even limited to animals; traffic noise has been shown to cause stress responses in plants too. Noise pollution can even affect disease ecology, in part due to its immunosuppressive effects as a stressor.
Adverse effects can occur with anthropogenic noise as low as 40 dB – not louder than the hum of a refrigerator, and lower than the typical noise within a few thousand feet of a major motorway. In their paper “Degradation of natural habitats by roads,” engineer Hossein Madadi and coauthors emphasized that roads cause not only structural fragmentation as physical barriers but also functional fragmentation. Functional fragmentation can occur when sensory pollutants, like noise, cause wildlife to avoid otherwise suitable habitat despite physical connectivity. Using a model based on the 40 dB effect threshold, Madadi and colleagues found that over one-third of their study area, the Irano-Anatolian Biodiversity Hotspot, suffered probable habitat loss due to traffic noise, even though road surfaces themselves covered only about one percent of the area.
The functional fragmentation caused by traffic noise can have adverse consequences for migratory animals, as “phantom road” experiments have demonstrated in the case of birds. To isolate the effect of noise from other disruptive effects of roads and traffic, ecologist Christopher McClure devised an experiment using playback of traffic noise in a roadless area. McClure and colleagues found that noise alone caused migratory birds to avoid otherwise suitable stopover habitat.
In a later experiment conducted in Japan, Masayuki Senzaki and colleagues used the phantom road technique to assess wider scope impacts of noise pollution on ecological communities. They found that traffic noise not only reduced the abundance and richness of forest bird species but also altered the community composition of grasshoppers and dragonflies, possibly due to changes in the top-down pressure exerted by the birds who prey upon them.
“Phantom roads” provide strong evidence that, due to noise alone, freeway traffic will continue to disrupt ecosystems even when wildlife crossings are established.
Autumn darter, a dragonfly endemic to Japan, photo by Alpsdake / Wikimedia, CC BY-SA 3.0
Of course, road traffic is not the only source of noise pollution that disrupts ecological communities. One natural experiment resulted from natural gas extraction in the forests of northern New Mexico: By comparing extraction sites with and without noisy compressors, researchers were able to control for the impact of physical habitat destruction and fragmentation. They discovered that the noise from the compressors alone seemed to reduce bird species richness.
Subsequent research uncovered additional downstream ecological consequences. Woodhouse’s scrub-jays were among the noise-avoidant birds, but they are also important seed dispersers for pinyon pines. Several years after the initial study of bird communities, plots with noisy compressors were found to have only a quarter of the number of pinyon seedlings as quieter control plots. Additional studies showed further that the juniper saplings were less abundant in noisy plots, likely due to these plots’ avoidance by other avian seed dispersers like mountain bluebirds.
Woodhouse’s scrub-jay, photo by Dennis Church, CC BY-NC-ND 2.0
The pinyon pine woodlands proved slow to recover even after the removal of the noise source. This slow recovery is likely due in part to the trees’ masting cycles, producing “bumper crops” of cones only every three to seven years; however, the jays’ excellent memory might also play a role, as biologist Jennifer Philips and coauthors noted. It is possible that these intelligent seed-caching birds remember areas where they experienced unpleasant noise and intentionally avoid returning.
Despite such striking consequences of anthropogenic noise, soundscapes have long been neglected in conservation. In a study published in Science in 2017, biologist Rachel Buxton and coauthors found that 63 percent of protected areas in the U.S. experienced at least a doubling of noise levels due to anthropogenic noise pollution. Even designated wildernesses were not immune: More than 12 percent of wilderness areas were found to experience “anthropogenic sound levels 3 dB above predicted natural levels, indicating that they are not entirely ‘untrammeled by man’ as defined by the Wilderness Act,” as the authors aptly noted.
Air traffic is one noise source that can intrude into wilderness areas. A 2009 report on noise pollution in parks found that even in Yellowstone’s backcountry, peak aviation noise was loud enough that “prey species could experience a 45 percent reduction in the distance at which they can hear a predator approaching, and predators that hunt using acoustic cues might experience a 70 percent reduction in search area.”
In Europe, a report published in 2025 revealed that 29 percent of land in the EU’s Natura 2000 network was “exposed to transport noise at levels that could negatively impact biodiversity,” while an additional 41 percent was “not currently quiet” but had the potential to be restored.
Glacier National Park, a designated Wilderness Quiet Park, photo courtesy U.S. Department of the Interior
Organizations like Quiet Parks International have brought attention to the importance of soundscapes as part of the wilderness experience, with programs like Wilderness Quiet Parks and Quiet Trails. The rewilding movement must follow suit: Minimizing noise pollution should be regarded as a non-negotiable goal for both “cores” and “corridors.” (In designing protected areas, we should also be mindful that even human recreational noise, such as vocal hikers and mountain bikers, counts as noise pollution from the perspective of wildlife; it can trigger anti-predator responses such as fleeing and avoidance, not only wasting energy but also causing functional habitat loss.)
Google Data Center, photo by Chad Davis / Wikimedia, CC BY 2.0
In light of modern society’s growing hunger for buzzing data centers, including on public lands in the U.S., attention to noise pollution has never been more essential. Exclusive focus on climate change can foster a misconception that data centers are okay if they’re powered by renewable energy, automotive traffic is fine if it’s electrified, and so on. However, just as fast-moving electric vehicles still produce tire noise, renewable-powered data centers will still be responsible for the loud hum of cooling units – the main contributor to data center noise pollution. Furthermore, the expansion of wind farms will be another significant source of noise in its own right, with probable adverse effects on wildlife.
I don’t claim to know what solution to offer to human societies that seem resigned to incessant noise. The goal of this article is merely to raise awareness about its importance for rewilding. The first step is recognizing the problem.
Kate McFarland is a former board member of The Rewilding Institute. Her rewilding-related interests subsequently settled on feathered fauna and flyway conservation, with accompanying interests in noise and light pollution mitigation, as well as non-anthropocentric conservation ethics.
