For birds living the city life, listening to the rhythm of the street might cause more than hearing loss, a new study finds—it might just shorten their lives.
As cities rise and expand rapidly, each new skyscraper and boulevard yields more than aesthetic changes, and with each new construction project comes a new headache, perhaps especially for birds. Food sources shift, prime nesting real estate changes and the clanging and banging cacophony grows louder and louder. Out in the real world, it’s hard to isolate which stressful factor is most damaging in the non-stop hustle of urban life, but researchers at Max Planck Institute for Ornithology in Germany were able to isolate the effects of noise pollution on zebra finches (Taeniopygia guttata) at different stages of life in their lab. The researchers report this week in Frontiers in Zoology that birds in a late juvenile stage of life were more vulnerable to a boisterous soundscape, showing a tell-tale sign of stress that is often linked to rapid aging and shorter lifespans.
“It’s a very provocative thought that noise pollution can affect how long you live,” says Rachel Buxton, a conservation biologist at Colorado State University who was not involved with the study. “Considering whether stress from noise would translate to humans certainly gives you something to think about.”
Previous studies have shown that noise is linked to several stress-related health problems in humans and animals alike. One indicator scientists frequently use to track degrading health is measuring the length of part of our DNA called telomeres. Telomeres are the caps at the end of chromosomes, kind of like the plastic at the tip on a shoelace. When telomeres shrink with time and eventually disappear, cells begin to age—not unlike when the plastic on a shoelace frays, causing it to slowly unravel.
In people, studies of pregnant mothers undergoing extraneous stress during pregnancy showed that the women gave birth to babies with shorter telomeres. In birds, recent fieldwork observing populations of great tits (Parus major) demonstrated that life in an urban environment can indeed shorten telomeres as well. The researchers were also able to show that birds with shorter telomeres disappeared from the overall population.
Building on past work, researchers working on the new study set out to determine whether noise alone, without air pollution or other negatives of city life, would have the same kind of shortening effect on telomeres. Furthermore, they wanted to know at what stage of life birds are most susceptible to stressful side effects of a noisy environment— specifically, city sounds recorded in Munich and played back randomly to mimic a typical summer day and night.
The team studied the hatchlings of three groups of birds, 263 in total. One group of nesting parents was exposed to noise during their breeding and birthing period, and the researchers continued to play the noises until the babies were 18 days old. They also exposed a second group, one composed of juveniles 18 days old and up—about the time young zebra finches typically leave the nest—to noise for about 100 days. The last group was exposed to no sound at all.
At 21 days old, bloodwork showed that each group of adolescent birds had telomeres about the same length. At 120 days old, however, the group of young birds that was exposed to noise in their later juvenile stage of life had much shorter telomeres than the birds whose parents had been exposed to noise.
This surprised the team, says Sue Anne Zollinger, co-author of the new study and a behavioral physiologist at Max Planck Institute for Ornithology. Previous work had suggested that the offspring of parents exposed to noise would have the shortest telomeres.
Perhaps, Zollinger says, the parents took extra precautions to shield themselves and their nests from noise in the aviaries while the teenage birds, so to speak, lived a little more recklessly in their newfound freedom.
Additionally, this later stage of youth is a naturally stressful time for teen birds: It’s when they leave the nest, figure out how to scavenge for food and learn to sing. Most birds, like humans, develop communication skills from tutors while most other animals will start barking, bellowing and bleating even without ever hearing others make a peep.
“They need to sing in order to court as well as engage in friendly and aggressive interactions,” says Zollinger. “Overall, it’s a sensitive time when the birds are trying to survive on their own and they have a lot of learning to do—not just vocal learning—but also just how to be a wild bird in general.”
Because the study began in 2014, most of the birds are about three or four years old now. On average, zebra finches can live to be eight years old, Zollinger says, so whether the birds’ shortened telomeres actually lead to shortened lives remains to be seen.
The thing about telomeres is that loss of length is not the end—an enzyme called telomerase can recover telomere length. But exactly what stimulates telomerase activity remains a mystery, and typically it becomes more difficult to repair cells and bounce back from adversity as we age.
In the meantime, continuing to narrow down what aspects of city life deal the most stressful blow could help inform city planners of how to build safer, quieter urban areas for our feathered friends, says Zollinger.