Galapagos birds exhibit ‘road rage’ due to noise

A new study has discovered that birds in the Galápagos Islands are changing their behaviour due to traffic noise, with those frequently exposed to vehicles showing heightened levels of aggression.

Published in the journal Animal Behaviour and led by experts from Anglia Ruskin University (ARU) and the Konrad Lorenz Research Centre at the University of Vienna, the research examined the impact of vehicle noise pollution on Galápagos yellow warblers (Setophaga petechia aureola), a songbird widespread on the archipelago.

The Galápagos Islands, located over 500 miles off the coast of Ecuador, are considered a natural living laboratory due to the large number of unique, endemic species. The Galápagos yellow warbler is genetically distinct from other yellow warblers found in the Americas and is classified as a subspecies.

A visit to the Galápagos Islands in 1835 helped inspire Charles Darwin to develop the theory of evolution by natural selection. However, recent decades have seen significant human population growth. Alongside a rise in tourism, the permanent population is increasing by over 6% per year, leading to more vehicles on the islands’ roads.

The new study involved researchers playing 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.

The researchers 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. 

Additionally, Galápagos yellow warblers on the more populous island of Santa Cruz increased the duration of their song when confronted by traffic noise. These findings support the idea that long-term selection based on noise experience, or an individual bird’s previous experience of noise, allows them to adapt and adjust the features of their songs.

Finally, the birds increased the minimum frequencies of their songs during the noise experiments, regardless of their territory’s proximity to the road, helping to reduce any overlap of their songs with the low-frequency traffic noise.

Co-author Dr Caglar Akcay, Senior Lecturer in Behavioural Ecology at Anglia Ruskin University (ARU), said: “Birds use song during territorial defence as an aggressive signal. However, if external noise such as traffic interferes with the signalling, effectively blocking this communication channel, increasing physical aggression would be an appropriate response.

“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.

“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.

“Our study shows the importance of considering behavioural plasticity in conservation efforts and developing strategies to mitigate the effects of noise pollution on wildlife. 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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