A study of Galápagos yellow warblers, a songbird widespread in the Galápagos Islands, are changing their behaviour due to traffic noise, with those frequently exposed to vehicles showing heightened levels of aggression. Researchers played bird songs from a speaker, simulating an intruder, accompanied by recorded traffic noise at 38 locations populated by Galápagos yellow warblers on the islands of Floreana and Santa Cruz – 20 sites were within 50 metres of the nearest road and 18 were over 100 metres away. They then measured song, typically used to ward off intruders, and physical, aggressive behaviours such as approaching the speaker closely and making repeated flights across it. During trials with traffic noise, the researchers found that Galápagos yellow warblers living in roadside territories showed increased aggression, but those living away from the roads showed decreased aggression relative to trials without noise. Importantly, the effect of living on a roadside territory was present even on Floreana Island, with only about 10 vehicles present on the island, suggesting even minimal experience of traffic affects responses to noise.