- A noisier world makes it challenging for birds, which primarily rely on sound to communicate, and many are forced to change their behavior to cope with their clamorous environment.
- A recent study looked at how traffic noise impacts communication in male Galápagos yellow warblers (Setophaga petechia aureola), a common resident bird on the islands, and found that traffic noise increases aggression in birds living closer to roads.
- With traffic increasing in the biodiversity-rich Galápagos, conservationists worry about the impact of noise on birds, especially the yellow warblers, which are also the most common roadkill.
When Leon Hohl and Alper Yelimlieş landed in the Galápagos in 2022 to volunteer in a decades-old nest survey project, they expected to look for Darwin finches and their babies. But that year turned out to be too dry for the finches to breed, and the two bird enthusiasts weren’t going to sit idle. Since they were in the Galápagos — nature’s “evolution laboratory” — they turned their attention to another bird: The Galápagos yellow warbler (Setophaga petechia aureola), a subspecies of the North American yellow warbler with elaborate, complex birdsongs.
Hohl and Yelimlieş, both from Austria’s University of Vienna, teamed up with their supervisors to understand how the soaring human numbers on the archipelago’s most populous island of Santa Cruz, and increasing vehicular traffic noise in the soundscape, impact the island’s resident birds.
“We were interested in how yellow warblers would respond to noise, depending on how much experience they had with noise,” Çaglar Akçay from Anglia Ruskin University, U.K., one of the supervisors, told Mongabay. “Noise is generally a stressor.”
In a study published recently in the journal Animal Behaviour, Akçay and his team examined the behavior of male Galápagos yellow warblers on two islands and found that birds living closer to roads with vehicular traffic were more aggressive than their counterparts living further away.
Between January and March of 2022, the researchers conducted a set of experiments in which they played pre-recorded male yellow warbler songs on a speaker and observed the birds’ responses to them. The recorded sound simulated an intruder yellow warbler claiming territory. They added traffic noise to some of the recorded warbler songs to imitate intruders in a noisy environment.
Galápagos yellow warblers have complex birdsongs. Image by Zoltan BAGOSI via iNaturalist (CC BY-NC 4.0), audio courtesy of Çaglar Akçay.
The researchers conducted the first set of trials on Santa Cruz Island, which is inhabited by more than 15,000 people (which inflates to around 30,000 when tourists are included) and around 1,000 vehicles. For the second set of trials, they chose Floreana Island, with a little more than 100 people and 10 vehicles. The researchers picked some sites very close to roads and others more than 100 meters (328 feet) away.
A male yellow warbler typically responds to other male yellow warblers that wander into its territory with songs to shoo them away. But in a noisy environment, where it’s difficult for the bird to be heard, a warbler is more likely to become more aggressive and approach the intruder. In the bird world, that’s a risky move — one that could escalate to a physical altercation and result in injury.
In their experiments, the researchers found that birds that lived closer to roads displayed heightened aggression by flying very close to and around the speaker emitting intruder calls, compared to those that lived further away from roads. They also found that males increased the minimum frequencies, or the lower pitch, of their song in response to noisy playback so they could be heard, and only males living away from the roads sang with higher peak frequencies — that is, higher pitch. Even though the birds were from the same populations, they behaved differently in their responses based on their prior experience dealing with noise, Akçay said.
But what stood out the most to the researchers was that birds living near roads on both islands displayed similar aggressive behavior, even though there was a sea of difference in the noise levels.
“We were expecting to find island [level] differences, which we didn’t,” Akçay said. “Even low amounts of traffic on Floreana seems to be enough for the birds to change their behavior.” However, males in Santa Cruz sang longer in response to noisy recorded songs than those on Floreana.
“Traffic noise impacts birds in many different ways—changes in behaviors like song frequency and timing, vigilance for predators, aggression or boldness, and ability to find and attract mates,” bioacoustics researcher Jennifer Phillips from Washington State University, who was not involved in the study, told Mongabay by email. She said that these results suggest “more aggressive individuals are able to live on territories that have noise, while less aggressive individuals are more likely to settle on quieter territories away from roads.”
With noise, birds and bird songs go out of tune
For birds, their songs are critical to most aspects of life — attracting mates, raising chicks and defending their territories — and, hence, making their song heard is crucial. While responses vary by species, most birds have figured out a way to cope with some levels of human noise by adjusting their frequencies, amplitudes, or aggression levels.
But some species are better at dealing with noise than others, according to Phillips.
“Many species may adjust their behaviors and be able to live near noise, but the most sensitive species are likely not able to change their behaviors or deal with the stress of daily noise interruptions,” Phillips said. “This is why cities or human impacted areas often have lower biodiversity, because more sensitive species are the first to go.”
The stress caused by noise and the resulting aggression takes a toll, too. It reduces the birds’ physical health and their ability to breed successfully.
“We’ll see more and more effects of this as humans alter the habitats,” Akçay said. “There [are] very few places on Earth where there’s no human noise.”
That effect is pronounced in the biodiversity-rich Galápagos, where the human population has increased 10-fold in the last 50 years, the number of tourists is soaring, and vehicles are rapidly multiplying. Santa Cruz saw a 57-fold increase in vehicular traffic between 1980 and 2013. A previous study found that the island’s birds are increasingly becoming roadkill, and that 70% of birds killed by traffic on Santa Cruz are yellow warblers. And as this study shows, noise is also impacting the warblers.
“Roads are not really going to be friendly to birds, ever,” Akçay said, adding that imposing speed limits could help. “Lower speed limits also mean lower noise [and] it can improve roadkill.”
Banner image: The Galápagos yellow warbler is a resident subspecies of the North American yellow warbler. Image by Nick Athanas via Flickr (CC BY-NC-SA 2.0).
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Citations:
Hohl, L., Yelimlieş, A., Akçay, Ç., & Kleindorfer, S. (2025). Galápagos yellow warblers differ in behavioural plasticity in response to traffic noise depending on proximity to road. Animal Behaviour, 123119. doi:10.1016/j.anbehav.2025.123119
Brumm, H. (2004). The impact of environmental noise on song amplitude in a territorial bird. Journal of Animal Ecology, 73(3), 434–440. doi:10.1111/j.0021-8790.2004.00814.x
Akçay, Ç., Porsuk, Y. K., Avşar, A., Çabuk, D., & Bilgin, C. C. (2020). Song overlapping, noise, and territorial aggression in great tits. Behavioral Ecology, 31(3), 807–814. doi:10.1093/beheco/araa030
García-Carrasco, J.-M., Tapia, W., & Muñoz, A.-R. (2020). Roadkill of birds in Galapagos Islands: a growing need for solutions. Avian Conservation and Ecology, 15(1). doi:10.5751/ace-01596-150119
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