City noise in the egg is already detrimental to the health of birds

City noise in the egg is already detrimental to the health of birds

Normal exposure to everyday city sounds has a major negative impact on bird young that are still in the egg. Australian and Spanish biologists wrote this down at the end of April Science after experiments with zebra finches. ‘Noise disturbed’ eggs more often do not hatch, and young that do hatch grow less well and have poorer blood values. Damage can even be seen at DNA level. And ultimately they reproduce less successfully as adults.

It has long been known that noise from human activities, even at relatively low noise levels, can be harmful to animals. Research on marine mammals, birds, frogs, fish and insects has shown that they communicate and behave differently when exposed to human sounds. It is clear that it causes stress to animals. But its influence on unborn and young animals has hardly been studied, the authors write Science. And certainly not in a way that excludes indirect effects: namely effects on the parents, which then affect the young.

The Australian and Spanish researchers therefore devised a series of experiments to rule out these indirect effects. They did this by removing the eggs from the parents at night and exposing them in an incubator to traffic noise or zebra finch song, both at moderate noise levels (65 dB, comparable to the noise level fifty meters away from a highway). A control group lay in a quiet incubator overnight. Other groups also received the same treatment between four and thirteen days after hatching.

Worn telomeres

The differences were large, the researchers said. In the silent group and the bird song group, almost all eggs hatched; in the traffic noise group only about 60 percent. On day twelve, young that had been exposed to traffic noise both before and after hatching were 11 percent smaller and more than 14 percent lighter than conspecifics that had heard equally loud parental sounds. Their telomeres (the DNA ends; a measure of ‘wear and tear’ of the DNA) were significantly shorter (more ‘worn out’). Their hematocrit (a measure of the amount of red blood cells) was significantly lower. And in the end, they had 59 percent fewer offspring over their entire lifespan.

The researchers also saw these negative effects, although less so, in birds that had only been exposed to traffic noise as eggs. Remarkable, they write, because until now biologists assumed that hearing in nest stayers (birds that do not leave the nest immediately after hatching) only develops after hatching. The influence of traffic noise on the chicks was additive: the more days of exposure, the greater the effect.

behavioral ecologistHans Slabbekoorn Those birds are our canary in the coal mine

In this test, the effect did not go through the parents (who can also be stressed by noise, which can influence the development of their young), but through the young themselves, the researchers concluded. According to them, it is still unclear exactly how this works. Such a large impact of noise levels that animals and humans experience on a daily basis “is worrying,” they write, and calls for measures to limit anthropogenic noise as much as possible, “not least during early development.”

“We should certainly take this seriously,” responds Hans Slabbekoorn, professor of acoustic ecology and behavior at Leiden University. He wrote a commentary in the study Science, but was not involved himself. “This is very urgent not only for animals in nature, but also for humans,” he says. “The World Health Organization (WHO) has published several reports since 2011 on the ‘healthy life years’ lost due to exposure to sounds of 65 dB and above. In many places in the city and along the highway it quickly becomes louder than that. And then we also go to pop concerts and often use headphones. All in all, that is a major damage that we do not take nearly seriously enough.”

What is special about the study with the zebra finches is the sophisticated experimental design, which avoided effects on the parents. “We have known for some time that there are major effects of noise on parent birds,” he says. “For example, our own research has shown that parents visit the nest more often in a noisy environment. Perhaps this provides some kind of compensation, because we found no negative effects on the growth and survival of the young.”

Not only loud sounds, but all sounds that require your attention, cost energy, he explains. “Sounds tax your working memory, so to speak. This means you can use it less effectively for other things. Just look at yourself: if you have to park backwards, you also want it to be quiet in the back seat.”

Constant extra burden on that working memory can cause stress in the long term, even unnoticed, according to Slabbekoorn. “And that has all kinds of effects. With these zebra finches, even into the next generation.”

Findings in animal research have led to adjustments here and there, especially for marine mammals. For example, engineers are looking for quieter techniques for piling in offshore wind farms. But how do these results with zebra finches relate to our own daily lives? “Those birds are our canary in the coal mine,” says the Leiden professor. “The whole stress system works in birds just like it does in us. So those effects undoubtedly exist for us as well.”

Noise in the incubator

And he’s not just talking about highways, pop concerts and headphones. According to him, a relevant context is, for example, the incubator department in the hospital. “Researchers have sometimes measured the sounds in such an incubator. It is a gigantic noise from ventilation, pumps and other machines, and those sounds also resonate extra in such a tank. You don’t want vulnerable babies to spend their first weeks like this, do you?”

Slabbekoorn draws a parallel with developments in anesthesia. “We used to think: you don’t have to anesthetize babies during an operation, because they don’t feel any pain anyway. Now we know better. But we still have incubators that are only equipped for temperature and monitoring, not for sound.”




SCIENCE