The Galápagos Islands have long been a showcase for how plants and animals adapt to their environment.
The menagerie of unusual species inhabiting these volcanic outcrops off the coast of Ecuador played a central role in Charles Darwin’s insight about how species form – evolution by natural selection. Most famous are the plethora of finches with beaks shaped to collect different kinds of seeds.
But there’s a new force at work on these remote islands. And like natural factors such as rainfall, there are signs that species are changing to adapt. That factor is people – or, more specifically, people in cars.
Unlike the legendary finches, this new insight relates to the Galápagos yellow warbler, a petite songbird that weighs little more than a quarter. The ubiquitous bird appears to tweak both its song and behavior depending on whether its living next to a road, scientists reported this month in the journal Animal Behavior.
The new work “highlights the significant impact of human activities on wildlife behavior, even in relatively remote locations such as the Galápagos Islands,” said Caglar Akcay, a behavioral ecologist at United Kingdom-based Anglia Ruskin University, who was involved in the study.
Human intrusions into the natural world have been known to alter animal behavior in all sorts of ways, whether it’s mountain lions shifting movements to avoid bright lights or animals being less skittish around predators.
In the case of songbirds, which rely on sound to do everything from find a mate to scare off rivals, the cacophony of the modern world is a major factor. Birds in urban places, for example, have been found to sing at a higher pitch.
Akcay and several other scientists wanted to know whether road traffic in the islands was having noticeable effects on songbirds there. While far less busy than a major city, some of the islands have experienced a surge in human activity. Between 1980 and 2013, the number of vehicles on the most populous island, Santa Cruz, grew from 23 to 1326.
To figure out whether this altered the behavior of the yellow warbler, the scientists created an experiment. They compiled a recording of sounds of vehicles driving down a road, and another of yellow warblers singing. Then they took these recordings to Santa Cruz and the much less populated island of Floreana. In 38 places where yellow warblers had been spotted, they set up little speakers and played just the birdsong on one day, and both the song and car noises on another. Then they watched and listened for the feathery inhabitants to react.
In nearly every case, a male warbler responded to the provocation. But how they reacted differed, depending on how close the location was to a road and what they were hearing.
Birds that lived within 50 meters of a road became more aggressive than usual when the traffic sounds were played with the songs, approaching the speaker more closely or flitting past it more often. By contrast, birds that lived further from a road became more subdued when songs were accompanied by traffic noises.
“Birds use song during territorial defense as an aggressive signal,” said Akcay. “If external noise such as traffic interferes with the signaling, effectively blocking this communication channel, increasing physical aggression would be an appropriate response.”
The change in behavior could matter to the birds. Singing is a relatively low-cost way to duel, while physical confrontations increase the risk of injuries.
It apparently doesn’t take a lot of traffic to spark this response. The more assertive response of road-dwellers was apparent even on Floreana, where there are fewer than a dozen vehicles and around 100 people.
There was some evidence that the more crowded conditions on Santa Cruz might have altered singing behaviors of birds. The birds on that island tended to sing for longer when traffic noise was played. Due to their greater exposure to traffic, the birds might have learned to lengthen their singing to increase the chance of being heard over the din.
Call it evolution by automotive selection.
Hohl, et. al. “**Galápagos yellow warblers differ in behavioural plasticity in response to traffic noise depending on proximity to road.**” Animal Behavior. March 20, 2025.
Image: AI-generated ©Anthropocene Magazine
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