Noise is an invisible pollutant, but its effects can be seen. To begin with, the natural soundstage changes, altering the behavior of animals and affects health of humans and other species. It is true that in cities noise pollution is usually overshadowed by other pollution such as air or water quality, but its consequences are equally tangible.
At the beginning of this century, studies on urban birds They found that noise caused by human activity causes birds to sing at higher frequencies to avoid masking traffic, a source of low-frequency noise.
What Paris has achieved. As collects the paper published in Oxford Academicthe French capital has been fighting noise for decades directly and indirectly, especially focused on traffic, which shows a transformation in its urban mobility: it has gone from having 250 kilometers of bicycle lanes in 2003 to 800 kilometers in 2023, recycling traditional traffic lanes, with sound-absorbing asphalt, lowering speed limits, the expansion of electric vehicles and the installation of acoustic chambers capable of detecting and fining the noisiest vehicles (the famous “Medusa radars“).
The result is obvious: the government agency Bruitparif demonstrates that Paris is today approximately three decibels quieter than it was almost 20 years ago (since 2008). It may not seem like much, but it is worth remembering that the decibel scale is logarithmic and that in practice this reduction represents approximately half of the previous sound intensity.
Why is it important. The WHO is clear: Noise is the second most harmful environmental stressor for health in Europe (behind air pollution) and prolonged exposure to it increases the risk of cardiac ischemia, hypertension and sleep disorders in humans. The European Environment Agency details in its 2025 report that noise contributes to 49,000 new cases of ischemic heart disease annually on the continent. The prestigious The Lancet states in this paper that nocturnal noise causes sleep fragmentation, which raises blood pressure and, in the long term, damages the endothelium.
If we stick to birds and their song, it is something like human language: they are culturally transmitted from generation to generation and changes in song are also learned by individuals of the same species in the environment. But it goes beyond changing a sound: it affects your ability to attract a mate, warn of danger, defend your territory or simply communicate. And be careful because this also affects other species such as whales because of the noise of the boats either the bats. This other one study published in Proceedings of the Royal Society B which analyzes 160 species of birds since 1990 found that noise significantly impacts communication, risk behaviors, feeding, aggression and physiology, with a clear negative effect on reproduction.
Context. He Noise Prevention Plan in the Environment of Paris seeks to transform the French capital into a more livable city, becoming a living laboratory where urban planning and sensory planning combine to try to curb the impact of decades of acoustic degradation due to automobile dependency.
For the study of Parisian birds, the great tit is the sentinel, using recordings of its songs both in the center of Paris and in the Fontainebleau forest as a wild reference. This observation is not new: already in 2006 a study showed that the chickadees that sing under the Eiffel Tower did so with a minimum frequency 400 Hz higher than those that sang in the Fontainebleau forest. This pattern has been replicated in other cities and species and the result is the same: it is common for birds to increase the minimum frequency of song in response to urban noise.
The pending subject. Even though noise has decreased, Parisian tits continue to sing with significantly higher minimum frequencies than non-urban birds, and these frequencies have not decreased along with noise reduction. The explanation, according to the research teamis the cultural mechanism: young birds learn to sing by imitating the adults in their environment and for decades the only adults available to teach them sang high because it was the only way to make themselves heard. Now the city is quieter, but there are no teachers who sing gravely to learn. The habit persists even if the original cause has diminished.
San Francisco in COVID-19 leads the way: during the pandemic background noise was reduced by about seven decibels and the white-crowned sparrow responded by singing at lower frequencies. Nature is speaking loud and clear: the reduction achieved by Paris is real but insufficient.
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Cover | Noureddine BOUABDALLAH and Alexander Kagan
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