a yellow warbler sits on a branch with its beak open, singing
The Galápagos yellow warbler is a genetically distinct subspecies of the yellow warbler, which might be familiar to residents of the United States. Alper Yelimlies
The Galápagos Islands are famous for their pristine, natural ecosystems. But even on this remote and mostly undeveloped archipelago, human activity is affecting animals.
Researchers recently discovered that traffic noise may be causing male Galápagos yellow warblers to behave more aggressively when defending their territories. Even exposure to just a handful of cars on a regular basis changed the birds’ habits, according to a new paper published last week in the journal Animal Behaviour.
For the study, scientists focused on the Galápagos yellow warbler (Setophaga petechia aureola), a small songbird that’s endemic to the archipelago. The Galápagos Islands, which famously inspired British naturalist Charles Darwin’s theory of evolution, are located roughly 600 miles off the coast of mainland Ecuador, in the Pacific Ocean.
Males have bright yellow feathers covering most of their bodies, with a reddish-brown “cap” atop their heads during the breeding season. They are territorial birds that defend their turf from other males. Typically, males will sing loudly to warn approaching intruders to stay away. But, if necessary, they will engage in physical fights.
“Birds use song during territorial defense as an aggressive signal,” study co-author Çağlar Akçay, an ecologist at Anglia Ruskin University in England, says in a statement. He and his team wondered whether traffic noise might be affecting the birds’ interactions. “If external noise such as traffic interferes with the signaling, effectively blocking this communication channel, increasing physical aggression would be an appropriate response.”
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To test this, they visited 38 yellow warbler nesting sites on two different islands: Santa Cruz Island, which has more than 15,000 human residents and more than 1,000 cars, and Floreana Island, which has less than 100 human residents and approximately ten cars. Some of the nesting sites were near roads (within 164 feet), while others were farther afield (more than 328 feet away).
At each site, they played two different types of audio recordings: one with the sound of a male Galápagos yellow warbler and traffic noises, and another with only the male bird call, unobscured by the sound of cars. Then, they watched to see how the birds responded.
The male Galápagos yellow warblers that lived near roads on both islands reacted more aggressively when they heard the recording of the intruding male alongside traffic. They approached the speaker and repeatedly flew by it—which researchers used as a proxy for physical aggression. The birds that did not live near roads, by contrast, behaved less aggressively when they heard the recording of the intruder and traffic noises.
It’s possible that the birds were flying closer to the speaker simply to make themselves heard over the din of traffic. But the males didn’t always sing as they approached.
And, even if the birds were flying closer simply to “talk it out” with the intruder, they might still be putting themselves in harm’s way, says Akçay to the London Times’ Akshay Raja.
“Getting closer might be interpreted as an aggressive signal,” he adds. “If you’re flying back and forth to defend your territory, some of these birds will have territories on either side of the roads, so they will actually have to fly over the road and they get killed by the vehicles.”
Indeed, the study’s authors note that the Galápagos yellow warbler is the most commonly killed bird on Santa Cruz Island’s main road.
Two yellow birds on branch
Galápagos yellow warblers are endemic to the Galápagos Islands. Çağlar Akçay / Anglia Ruskin University
Researchers noticed other changes in the birds’ behavior, which they call “behavioral flexibility.” Male birds increased the minimum frequencies of their songs when they heard the recordings that contained traffic sounds, regardless of where they lived. They likely made this change so their vocalizations did not overlap with the low-frequency vehicle sounds, the scientists suggest.
The birds on Santa Cruz Island sang for longer durations when they heard the traffic noise recordings, while the birds on Floreana Island sang for shorter durations. Birds that lived far from roads on both islands also increased the peak frequency of their vocalizations.
These findings suggest the birds are trying to “cope” with the road noise by adjusting their song, even on the sparsely populated Floreana Island, per the study. The team hopes future conservation efforts will include strategies for mitigating noise pollution, which seems to affect wildlife behavior even in relatively remote destinations.
“Even that little experience [of traffic on Floreana Island], apparently, has some effect,” Akçay tells the Guardian’s Nicola Davis. “We have to think about noise pollution even in places like Galápagos, I think, and the impact of noise pollution on the unique species there.”
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Sarah Kuta | READ MORE
Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.
Filed Under: Animals, Biology, Birds, Cars, Charles Darwin, Conservation, Ecology, Ecuador, Evolution, Land Birds, New Research, Wildlife, Zoology