The zebra finch, which hears the sounds of cars and motorcycles in the egg, still experiences this as an adult

New research reveals that birds exposed to traffic noise while in eggs are damaged for life.

This way, once the birds emerge from the egg, they grow more slowly. When they finally reach adulthood, they also become less able to reproduce. The researchers reached these conclusions in the journal Sciences.

an experience
Scientists base their conclusions on experiments conducted on Australian zebra finches. In these experiments, zebra finch eggs that were scheduled to hatch were removed from the nest at night and exposed to silence, zebra finch songs, or traffic noise (similar to the traffic noise to which urban birds are exposed) for 4.5 hours. At the end of the night, the eggs are placed back in the nest, where the parents care for them during the day. The researchers also performed the same experiment on zebra finches that had just hatched from the egg, but the scientists were not exposed to traffic noise, silence, or zebra finches' songs while in the egg. Then there was a third group of zebra finches that were exposed to traffic noise, songs of their own species, or silence, both in the egg and in the days after they hatched.

He follows
All the zebra finches were then monitored for a longer period of time – at least until they reached adulthood for some time. During that period, the growth of the young was monitored, among other things. 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 exposed to traffic noise while in the egg and/or shortly after hatching appear to grow less. “Individuals who were exposed to traffic noise as fetuses and young children were 11 percent smaller and 14.5 percent lighter than those who were never exposed to the 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. The researchers explained in their study that “telomere length reflects the extent of an individual’s exposure to cell damage.” The following applies: the shorter the telomeres, the more cell damage. 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 zebra finches behaved as adults after being exposed to noise in the egg and/or after they hatched from the egg. It leads to a rather shocking discovery. Because exposure to noise before and after birth appears to reduce the reproductive success of birds. “Individuals exposed to noise before and after birth produced, on average, 59% less independent offspring than those who were 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 evolution and reproduction of species; Studies have previously been published suggesting something like this. But it is still not clear exactly how noise affects animals' growth and reproductive success. For example, it was not known whether sound waves directly affected the development of young animals or whether they did so indirectly, for example because in principle they did not disturb the young, but the parents (or the behavior of these parents), as a result of which they received Young people cared less well and therefore felt their development was less good. The new research – in which only young zebra finches and not their parents were exposed to traffic noise – suggests that noise actually has a direct effect on the development of young birds.

There is no protective effect
Another interesting conclusion the researchers can draw from their study is that prenatal noise exposure does not protect birds from the effects of postnatal noise exposure. It was previously thought that birds exposed to noise in the egg are better prepared for a noisy environment. Therefore, when they are exposed to noise again later in life, they experience fewer negative effects from that noise. But this turned out not to be the case. It turns out that zebra finches exposed to noise in the egg experienced just as many harmful effects from the noise they heard as chicks as birds that were treated only to traffic noise as chicks.

The results are very disturbing. Because traffic noise appears to be detrimental to the growth of zebra finches and even affects the number of zebra finches that are born later. “The results suggest that the acoustic environment for breeding birds in cities and along highways needs to be better managed,” Hans Slabykorn, professor of acoustic ecology and behavior at Leiden University, wrote in response to the new research. According to him, it is also not unlikely that the development of other species – including mammalian species, such as humans – could be hindered by traffic noise. According to him, the research may also indicate this
“Acoustic comfort in hospital environments for pregnant women and children deserves special attention.”