New research reveals that birds exposed to traffic noise while in eggs are scarred for life.
This way, once out of the egg, the birds grow more slowly. And when they finally reach adulthood, they are also less able to reproduce. Researchers come to these conclusions in the magazine Science.
Experiment
The scientists base their conclusions on experiments with Australian zebra finches. In these experiments, zebra finch eggs that were due to hatch were removed from the nest at night and exposed to silence, zebra finch songs, or traffic noise (similar to traffic noise that urban birds are exposed to) for 4.5 hours. At the end of the night, the eggs were placed back in the nest, where the parents cared for them during the day. The researchers also performed the same experiment with zebra finches that had just hatched from the egg, but had not been exposed by scientists to traffic noise, silence or zebra finches’ songs while they were still in the egg. And then there was a third group of zebra finches that were exposed to traffic noise, songs of their own kind or silence, both in the egg and in the days after they hatched.
Followed
All zebra finches were then monitored for a longer period – at least until they reached adulthood for some time. During that period, the growth of the little ones was monitored, among other things. And at a later stage, the fitness – or reproductive success – of the birds was also examined.
Results
The results are clear, the researchers write in their study. For example, birds that were exposed to traffic noise while in the egg and/or shortly after hatching appeared to grow less well. “Individuals exposed to traffic noise both as embryos and as nestlings were 11 percent smaller and 14.5 percent lighter than those never exposed to noise.”
Telomeres
In their study, the researchers also looked at the length of the birds’ telomeres. Telomeres are protective caps on the ends of chromosomes. “Telomere length reflects the extent to which an individual has experienced cell damage,” the researchers explain in their study. The following applies: the shorter the telomeres, the more cell damage. And the nestling chicks that were exposed to traffic noise while in the egg or shortly after hatching appeared to have shorter telomeres than birds that were not exposed to traffic noise.
Reproduction
The researchers continued to monitor the birds, because they were also very curious about how the zebra finches would fare as adults after they had been exposed to noise or not after they had been exposed to noise in the egg and/or after they had hatched from the egg. It leads to a rather shocking discovery. Because both prenatal and postnatal exposure to noise appeared to reduce the reproductive success of the birds. “Individuals exposed to noise both pre- and postnatally produced, on average, 59 percent fewer independent offspring than those never exposed to noise in their early years,” the researchers wrote.
Immediate effect
The new research is certainly not the first study to show that noise can be harmful to the development and reproduction of species; studies have previously been published suggesting something like this. But it remained unclear exactly how noise affects the development and reproductive success of animals. For example, it was unknown whether the sound waves directly affected the development of young animals or did so indirectly, for example because they did not in principle disturb the young, but the parents (or the behavior of those parents), as a result of which the young received less good care and therefore felt develop less well. The new research – in which only the young zebra finches and not their parents were exposed to traffic noise – now hints that the noise actually has a direct influence on the development of young birds.
No protective effect
Another interesting conclusion that the researchers can draw from their study is that prenatal noise exposure does not protect birds against the effects of postnatal noise exposure. It was previously thought that birds that are exposed to noise in the egg are better prepared for a noisy environment. And therefore, when they are exposed to noise again later in life, they experience fewer negative effects from that noise. But that turns out not to be the case. Zebra finches that were exposed to noise in the egg turned out to experience just as many adverse effects from the noise they heard as nestlings as birds that were only treated to traffic noise as nestlings.
The findings are quite disturbing. Because traffic noise appears to be harmful to the development of zebra finches and even affects how many young the zebra finches subsequently give birth to. “The results suggest that the acoustic environment of breeding birds in cities and along highways needs to be better managed,” writes Hans Slabbekoorn, professor of Acoustic Ecology and Behavior at Leiden University, in response to the new research. According to him, it is also not implausible that the development of other species – including mammal species, such as humans – can also be hindered by traffic noise. And according to him, the research may also hint at that
“the acoustic comfort in hospital environments for pregnant women and babies deserves special attention.”
