Traffic noise pollution stunts growth in baby birds, even while in the egg, research has found.
Unhatched birds and hatchlings exposed to noise from city traffic experience long-term negative effects on their health, growth and reproduction, the study found.
“Sound has a much stronger and more direct impact on bird development than we previously knew,” says Dr Mylene Mariette, an avian communication expert at Deakin University in Australia and a co-author of the study, published in the journal Science. “It would be wise to work more to reduce noise pollution.”
A growing body of research suggested that noise pollution causes stress to birds and makes communication more difficult for them. But whether birds are already distressed at a young age because they are affected by noise, or because of how noise disrupts their environment and parental care, was still unclear.
Mariette’s team regularly exposed zebra finch eggs for five days to either quiet, soothing playbacks of zebra finch songs, or recordings of city traffic sounds such as revving cars and passing cars. They did the same with newborn chicks for about four hours a night for up to 13 nights, without exposing the birds’ parents to the sounds.
They observed that the birds’ eggs were almost 20% less likely to hatch when exposed to traffic noise. The chicks that did hatch were more than 10% smaller and almost 15% lighter than the other hatchlings. When the team analyzed their red blood cells and their telomeres – a stretch of DNA that shortens with stress and age – they were more eroded and shorter than their peers’.
The effects persisted even after the chicks were no longer exposed to noise pollution, and carried over into their reproductive age four years later. The birds that were disturbed by noise during the early stages of their lives produced less than half as many offspring as their counterparts.
“We expected certain effects, but we didn’t expect them to be this strong,” Mariette said, especially since the exposure to noise pollution was relatively mild and for only four hours a day. “It was really quite impressive.”
“We generally accept, based on numerous studies, that very young birds, especially in the egg, have very poor or no sensitivity to sound,” says Robert Dooling, an animal hearing expert from the University of Maryland in the US, who is not involved at the study. But “this study raises the specter of broad, negative, lasting effects of noise on development”.
Hans Slabbekoorn, a professor of acoustic ecology and behavior at Leiden University in the Netherlands who was not involved in the study, said he was particularly surprised. When his team conducted experiments exposed chicks and their parents to moderate noise pollution, they found no impact on the growth of the chicks.
Slabbekoorn speculated that changes in the behavior of the parents – such as how they take more care of their nests – may have avoided or compensated for the negative effects of noise on the chicks.
to newsletter promotion
“Indeed I did not expect [such a] big impact necessarily,” Slabbekoorn said. It is the cumulative nature of these negative effects that “may end up being the most problematic”, he added. “Especially when noisy conditions are frequent or persistent, such as with birds living in noisy neighborhoods, near airports or busy highways.”
His research also found that birds at airports are exposed to such loud noise levels that they can be partially deaf.
More data are needed to establish how many birds and to which species these levels apply, and it remains unclear whether it is the loudness, the pattern, the pitch or other elements of traffic noise that disturb the young birds, or the mechanism behind the observed effects.
