'Alarm Bells' as Scientists Discover Threat to Birds

Baby birds may be negatively affected by the noise of traffic, even when still inside their eggs.

The noises of cars and other motor vehicles heavily interfere with the development of these bird chicks, and can lead to long-term harm, according to a new paper in the journal Science.

This marks the first study that has explored the effects of traffic noise on baby birds when their mothers weren't also exposed to the noise, as has been the case in most previous studies.

Traffic noise has been established by past research to increase the stress levels of adult birds, as well as delayed mate attracting and nest building. This is often due to the birds' communication via song being drowned out by the noise pollution.

The researchers—hailing from Australia's Deakin University in Victoria—investigated how wild zebra finch babies would be affected after being exposed to traffic noise, as well as the song of other zebra finches and silence, while still within their eggs and just after hatching.

The researchers found that, if the eggs were exposed to traffic noise for five days before hatching, they were less likely to hatch than when exposed to native songs of their species.

"Both traffic noise and song were played at the same moderate amplitude—65 decibels, which is similar to a conversation level—but something about the acoustic characteristics of the noise caused embryonic death," Mylene Mariette, a researcher at Deakin University, said in a statement.

"After hatching, the chicks were reared normally by the zebra finch parents. However, to expose the nestlings to noise, without exposing the parents, we took the babies away during the night, and exposed them to sound in the absence of the parents."

The researchers also found that the hatched chicks that had been exposed to the traffic noise experienced issues with their development to adulthood, including reduced growth in the nest.

"Nestlings exposed to noise rather than song were slower to grow and showed more severe signs of cellular damage," said Mariette. "These negative effects were the result of both previous noise exposure before hatching and current exposure during the nestling stage."

Additionally, these effects were long-term, impacting the growth of the noise-exposed birds long into adulthood.

"Once the chicks had left the nest, they were reared together in an aviary and not exposed to any playback," said Mariette. "One month after the end of exposure, we measured the juveniles again and found that noise-exposed chicks were no longer smaller than their song-exposed siblings, but the impact on their physiology had worsened. And even a year later, once the birds were adults, the cellular impact of noise was still clearly visible."

The experimental chicks were then allowed to breed with each other in aviaries, with the researchers studying which were the most successful at mating and producing chicks. They saw that the birds that had been exposed to traffic noise in the egg and as a chick produced only half as many offspring as those who had not experienced traffic noise. This effect was seen not only for their first breeding season but also later in life, even after they had already produced offspring.

The researchers still aren't sure why traffic noise has such an effect on birds. However, another study by Mariette found that the brain is wired in such a way that sound can have a direct impact on the body's physiology.

"Whatever the mechanism, an impact of such magnitude in a songbird, is highly concerning," said Mariette. "We may wonder what impact noise has on species for which embryos unambiguously perceive sounds. Among many other species, including humans, fetuses become responsive to external sounds in the last trimester of gestation."

This research highlights how anthropogenic noise is impacting wildlife, and therefore the need to reduce noise pollution for the sake of animals that share our space.

"This study therefore rings alarm bells about the impact of noise pollution on biodiversity and highlights the urgent need for noise reduction measures, for the benefit of humans and wildlife alike," Mariette said. "Although many solutions already exist, such as using electric vehicles in cities, maintaining trees and hedges along roads to act as noise barrier, favoring train over truck transport for goods, we should but also keep our city parks and own gardens quiet by avoiding noisy tools, especially leaf blowers."

The study also raises questions about whether human embryos could be affected by noises while still inside the womb.

"The study of Meillère et al. on zebra finches reinforces the notion of negative noise impact on chicks as they develop in the egg, an effect that extends to prenatal exposure to noise in other species, including humans," Hans Slabbekoorn, a researcher at Leiden University in the Netherlands, wrote in an accompanying Perspective article for the journal Science. "The findings suggest that the acoustic environment of breeding birds in cities and along highways should be better managed, and that the acoustic comfort in hospital environments for pregnant mothers and babies warrants special attention."

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