Traffic noise is making these Galápagos birds more aggressive

While actual road rage is primarily a human trait, some birds on the Galápagos Islands are experiencing their own issues with traffic. Galápagos yellow warblers (Setophaga petechia aureola) that are exposed to noisy traffic appear to show heightened levels of aggression. The findings are detailed in a study published March 20 in the journal Animal Behaviour.

“Birds use song during territorial defence as an aggressive signal,” Caglar Akcay, a study co-author and behavioral ecologist at Anglia Ruskin University in the United Kingdom, said in a statement. “However, if external noise such as traffic interferes with the signalling, effectively blocking this communication channel, increasing physical aggression would be an appropriate response.”

A world-renown “natural living laboratory,” the Galápagos Islands are over 500 miles off the coast of Ecuador. During his famed voyage to the archipelago aboard the HMS Beagle, the Galápagos helped inspire Charles Darwin’s theory of evolution by natural selection. The archipelago is home to a large number of unique and endemic species including giant Galápagos tortoise, marine iguana, flightless cormorant, and the Galápagos yellow warbler in this new study. The small yellow songbird is widespread on the archipelago. It is also genetically distinct from yellow warblers found elsewhere in the Americas and is classified as a subspecies.

However, the human population and impacts on the Galápagos has significantly grown in recent years. Alongside a jump in tourism, the population of permanent residents is also increasing by over 6 percent per year, leading to more motor vehicles around the islands. 

This new study took a closer look at the impact of vehicle noise pollution on the Galápagos yellow warblers. To stimulate the sound of an intruder, the team played bird songs from a speaker and recorded traffic noise. These noises were recorded at 38 locations populated by Galápagos yellow warblers on the islands of Floreana and Santa Cruz. Twenty of the sites were within 164 feet (50 meters) of the nearest road and 18 were over 328 feet (100 meters) away.

The team then measured their song–which is typically used to ward off intruders–and their physical and aggressive behaviors. These actions include making repeated flights across the speaker or approaching it closely.

During trials that included traffic noise, the team found that Galápagos yellow warblers living in roadside territories showed increased aggression. Those living away from the roads had a decreased aggression relative to trials without noise from cars.

“Our results show that the change in aggressive responses in yellow warblers occurred mainly near roads. Birds occupying roadside territories on both islands, and therefore having regular experience of traffic noise, may have learned to increase physical aggression when the territorial intrusion was accompanied by traffic noise,” said Akcay.

[ Related: Noise pollution messes with beluga whales’ travel plans. ]

This effect of living on a roadside territory was even present on Floreana Island, which only has about 10 vehicles on it. According to the team, this suggests that even minimal experience of car traffic affects responses to noise. 

The Galápagos yellow warblers on the more populous island of Santa Cruz also increased the duration of their song when confronted by traffic noise. Long-term selection based on noise experience, or an individual bird’s previous experience of noise could allow the birds to adapt and adjust parts of their songs.

“We also found some evidence of birds trying to cope with noise by adjusting their song, with yellow warblers in all habitats increasing the minimum frequency of their songs to help them be heard above the traffic noise,” said Akcay.

The birds also increased the minimum frequencies of their songs during the noise experiments, whether or not their territory was close to the road. This helped reduce any overlap of their songs with the low-frequency traffic noise.

“Our study shows the importance of considering behavioural plasticity in conservation efforts and developing strategies to mitigate the effects of noise pollution on wildlife,” said Akcay. “It also highlights the significant impact of human activities on wildlife behaviour, even in relatively remote locations such as the Galápagos Islands.”

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