Some bird species adapt perfectly to urban environments to the point of becoming pests (pigeons and parrots are some well-known examples). However, pollution and the lack of green spaces in cities make the presence of a wide variety of common birds in rural areas almost impossible.
A study co-led by a researcher from the Doñana Biological Station (EBD-CSIC) and whose results were published this week in the prestigious journal Science provides new data that may help explain why some birds have little success in the cities. The answer lies in the noise caused by traffic and its effects on the reproduction and development of chicks.
Various studies have linked excess noise (for example that existing in some urban environments) with health in humans. There is less data on the damage of this type of pollution, noise, on wild species. The new study led by Mylene Mariette, researcher at the Doñana Biological Station (EBD-CSIC) and Deakin University (Australia), and Alizée Meillère, scientist at Deakin University, demonstrates that exposure to traffic noise in birds interferes directly with development, causing serious and lasting harm to individuals.
The CSIC points out in a note presenting these results that previous studies had shown that “in noisier environments, fewer bird eggs hatch, and the incidence of delivery of dead fetuses in human beings increases.” However, these studies “could not separate the effect of noise on the mother from the effect on her offspring, because in all studies, both the young and the parents were exposed to noise. The new research “reveals for the first time that noise is harmful to the young, even when the mother is not exposed to the noise.
Because bird embryos develop outside the mother’s body and can be artificially incubated, it is possible to manipulate the embryos’ experience without manipulating the mother. The scientific team took advantage of this to expose zebra finch eggs, an Australian bird, to sounds. “We showed that, under optimal incubation conditions, eggs are less likely to hatch when exposed to traffic noise for five days before hatching than when exposed to the song of the species,” explains Meillère. Both traffic noise and singing were played at the same moderate amplitude (65 dB, similar to conversation level), but something about the acoustic characteristics of the noise caused embryonic death.
After hatching, the chicks were raised normally by the zebra finch parents. However, to expose the chicks to noise, without exposing the parents, the scientific team took the chicks overnight and exposed them to acoustic recordings in the absence of the parents.
Being exposed to noise at night in the chick phase also had a negative impact on growth and physiology. “Chicks exposed to noise grew worse and also showed more serious signs of cellular damage than those exposed to singing, such as a more rapid shortening of telomeres, which are the protective ends of chromosomes,” explains the researcher. These negative effects were the result of both previous exposure to noise before hatching and current exposure during the chick stage.
And these negative effects did not end when noise exposure stopped. Once the chicks left the nest, they were all raised together in an aviary and not exposed to any recordings. One month after the end of the exposure, the researchers measured the juveniles again and found that the noise-exposed individuals were no longer smaller than their song-exposed siblings, but their physiological state had worsened. And even a year later, once the birds were adults, the cellular impact of the noise was still clearly visible.
Did that persistent impact matter on physiology? To find out, once the birds were adults, the scientific team gave them the opportunity to breed freely in aviaries, to see who was most successful. “The results were impressive. “Finches exposed to noise before and after hatching produced only half as many offspring as those that never experienced traffic noise,” says Mariette. “This was observed in young adults during their first breeding season, but also later in life, in mature adults.”
This study reveals that noise directly and profoundly interferes with development, with lifelong consequences. One question that arises is why. What makes traffic noise so harmful to developing youth? While there is still no answer, a synthesis by Mariette, published this month in the Journal of Experimental Biology, highlights how the brain is specifically designed to allow a direct impact of sound on physiology, and how even plants and cells They are sensitive to sound and vibrations.
“Whatever the mechanism, an impact of such magnitude on a songbird, which according to many researchers cannot hear sounds until a few days after hatching, is very worrying,” says Mariette. “We can ask what impact noise has on species whose embryos perceive sounds unambiguously. Among many other species, this includes humans, in which fetuses respond to external sounds in the last trimester of gestation.”
In conclusion, this study raises the alarm about the impact of noise pollution on biodiversity and highlights the urgent need for noise reduction measures, for the benefit of both humans and wildlife. Many solutions already exist. They include the use of electric vehicles in cities, maintaining trees and hedges along roads to act as a noise barrier, favoring the transport of goods by train over the truck, but also simply keeping urban parks quiet. and the gardens themselves, avoiding noisy tools and especially leaf blowers.
