European Robins are well known for their fierce territorial behaviour, but a new study has cast light on how the sound of traffic influences levels of aggression in the species.
Previous studies have shown that urban robins are more inclined to get physical in defence of their territory than birds in the countryside, adapting their song, approaching the rival with swaying visual displays, then going in for an attack if necessary.
A 3D-printed replica of a robin was placed within a city park in Istanbul near busy roads and in a quiet wood on the outskirts of the city. The scientists from Anglia Ruskin University in the UK and Turkey's Koç University equipped the plastic bird with a speaker playing song of the species, while another speaker in the area played the sound of traffic noise.
European Robins in more rural environments became more aggressive with artificially increased traffic noise (Ian Bollen).
Dr Çağlar Akçay, senior lecturer at Anglia Ruskin University and lead author of the study, said: "In normally quiet surroundings, we found that additional traffic noise leads to rural robins becoming more physically aggressive, for instance approaching the model bird more closely."
By contrast, playing extra traffic noise in the city environment did not increase levels of aggression. Instead, the birds reduced their singing, hinting that they had learned to cope with brief increases in noise pollution.
Dr Akçay said: "The chronic high levels of noise that exist day and night in urban habitats, such as from traffic or construction equipment, may permanently interfere with the efficient transmission of acoustic signals and this is likely to be the key reason why urban robins are typically more aggressive than rural birds."
The team suggested that increased aggression would not make day-to-day life easy for the robins, and could even put individual birds at greater risk of predation as they focus on and move in on a rival bird.
Önsal, Çağla, Alper Yelimlieş, and Çağlar Akçay. 2022. Aggression and multi-modal signaling in noise in a common urban songbird. Behavioral Ecology and Sociobiology 76.7: 1-10. DOI: https://doi.org/10.1007/s00265-022-03207-4