The "Invisible Pollution" Disrupting Bird Parenting — Is There a Risk of Birdsong Disappearing? The Severe Impact of Noise Pollution on Birds and Possible Solutions

The "Invisible Pollution" Disrupting Bird Parenting — Is There a Risk of Birdsong Disappearing? The Severe Impact of Noise Pollution on Birds and Possible Solutions

We have become too accustomed to the sounds of the city. The sound of engines, the noise of tires on the road, the clanging of construction, and delivery trucks in the middle of the night. While these may serve as "everyday background music" for humans, for birds, they can become noise that disrupts their very "life infrastructure."


This is because birds read the world not only with their eyes but also with their "ears." Whether it's finding a mate, defending their territory, noticing predators, or chicks expressing hunger, sound plays a crucial role. When strong noise overlaps with the environment, it drowns out this information. This can lead to changes in behavior, physiological responses, and ultimately affect their "survival report card" in terms of reproduction and growth.


Research has shown that "the impact of noise is widespread, deep, and predictable."

The analysis by a research team centered at the University of Michigan took a broad view of this issue. They compiled over 150 studies published since 1990, integrating findings on how noise affects behavior, physiology, and reproduction (fitness) in 160 bird species across six continents. The study stands out by extracting common global trends rather than focusing on specific locations or species.


The conclusion is simple. Human noise alters the multifaceted responses of birds, and some of these responses are directly linked to "outcomes" like reproduction and growth.


Moreover, it's crucial to note that which birds are more susceptible to these impacts is influenced by the "traits" of the species.


It's not just "songs not being heard": Birds' bodies are shaken by stress responses

When considering the impact of noise, the first thing that comes to mind is the disruption of communication, such as "songs not being heard" or "courtship failing." While this is significant, it's not the only issue.


Recent studies have shown that noise can affect physiological indicators such as stress-related hormones in birds (e.g., corticosterone). Chronic noise has been reported to alter baseline levels and acute stress responses.


If stress responses change, it can affect foraging, vigilance, and parental care behavior, which in turn impacts chick growth and body condition. Some studies have discussed the possibility that noise is related to parental behavior and chick growth and oxidative stress.

 
It's not just about "changing the way they sing because they can't be heard," but the very "foundation" of daily decision-making and energy allocation is shaken.


Birds in urban areas tend to have higher stress hormones, and differences arise based on "nest type"

One specific trend revealed by the integrated analysis is that birds living in urban environments tend to have higher stress hormones. While noise is an inevitable part of urban life, it can become a chronic burden for birds.


Another interesting finding is the difference in "nest type." Birds that nest in cavities, such as tree holes or nest boxes, tend to be more negatively affected in terms of growth compared to those with open nests.

 
Intuitively, one might think "it's quieter inside a hole," but reality is not that simple. Cavities have unique sound reflections and low-frequency transmission, which can create different distortions in parent-offspring communication and the perception of warning sounds. Additionally, species with limited nesting site options may find it harder to avoid noisy areas.


There are multiple routes to "declining reproduction": abandonment, growth delay, communication failure

The impact on reproduction is not just a straightforward decrease in eggs or chicks. For example, studies that experimentally introduced traffic noise reported that in some species, reproductive success decreased and nest abandonment during the incubation period increased.

 
On the other hand, in other species, the impact may manifest more in changes in chick growth or stress indicators rather than reproductive success itself. In other words, "where it hits" varies with the combination of species traits and environmental conditions, which is why the perspective of "predicting based on traits" holds value.


But here's the hope: Noise is an environmental issue that can be "technically reduced"

Many environmental issues have complex causes and tend to require massive countermeasures. But noise is different. The co-author of the study points out that the solutions are already at hand, describing it as "relatively low-hanging fruit." Noise can be reduced through materials, design, and infrastructure construction.


For example, in urban planning,

  • speed management and road surface improvements (reducing tire noise) around residential areas, parks, and green spaces

  • optimizing the placement of sound barriers and planting strips (designing based on "sound pathways" rather than "appearance")

  • optimizing construction times and methods (operations considerate of breeding seasons)

  • incentives for introducing quiet pavement and noise-reducing equipment
    These are feasible measures. Just as materials and construction methods have been devised to reduce bird collisions, "sound" can also become a target for design.

The significance of us "regaining silence" extends beyond just birds

Birds are also "indicators" sensitive to environmental changes. Reducing noise not only helps bird parenting but also improves human quality of life (sleep, concentration, stress).


Above all, reducing "burdens that are left unaddressed despite knowing the solutions" can be the shortest path to recovering biodiversity. While it is natural to focus on major issues like land alteration and pesticides amidst the global decline of bird species, managing the often-overlooked factor of "sound" holds significant value.


SNS Reactions

Examples of actual posts observed

  • In posts from science news accounts, summaries like "integrated over 150 studies, showing noise impact on 160 species," "stress and reproductive impacts in urban environments," and "can be mitigated through design and materials" are shared, receiving reactions (likes).

Typical reactions on SNS (typical patterns from the content of the article)

  • "Birds use sound as an 'information network,' not just for singing... no wonder noise is fatal."

  • "I thought construction and roads were unavoidable, but if measures can be 'done at low cost,' they should be implemented."

  • "Loud motorcycles at night are actually bad for both birds and humans."

  • "Surprising that birds in nest boxes are more affected. Is 'quietness of location' important for conservation nest box placement?"

  • "It's strange that noise, despite being a pollution, isn't as talked about as air pollution."
    ※The above are representative reaction examples expected from the article's points (sound masking/urban stress/feasibility of measures/species differences).


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