Robins in rural areas become more physically aggressive when exposed to traffic noise, one study suggests.
Red-breasted birds are fiercely territorial and rely on cues, both visual and audible, to indicate their territory and keep other individuals away.
They change their behavior when threatened.
Researchers believe that while urban robins are used to temporary increases in noise levels and have learned to keep them out, rural robins instead compensate with increased physical aggression.
In one study, scientists from Anglia Ruskin University and Koç University in Turkey studied the behavior of male European robins (Erithacus rubecula) living in urban and rural areas.
They measured aggression towards an intruder using a 3D model of a robin.
The model robin was accompanied by recordings of robin songs, while additional traffic noise was added via a separate loudspeaker nearby.
By recording the birds’ behavior during interactions with the simulated intruder, the researchers noted that urban robins typically displayed more physical aggression than rural robins.
However, rural robins have become more aggressive with the addition of traffic noise.
Scientists believe that physical displays of territoriality increase because traffic noise interferes with robins’ signaling behavior using song.
In addition to tailoring their songs to ward off intruders, robins adopt specific visual displays during territorial interactions.
These include waving and displaying the red feathers on their necks, as well as approaching their opponent and attempting to drive them off.
Dr Caglar Akcay, senior lecturer in behavioral ecology at Anglia Ruskin University and senior author of the study, said: ‘We know that human activity can have a significant impact on the long-term social behavior of wildlife, and our findings show that human-made noise can have a range of effects on robins, depending on the habitat in which they live.
“In normally quiet environments, we have found that additional traffic noise leads rural robins to become more physically aggressive, for example by approaching the model bird more closely, and we believe this is because the noise interferes with their communication.
“Chronic high levels of noise that exist day and night in urban habitats, for example from traffic or construction equipment, can permanently interfere with the efficient transmission of acoustic signals and this is probably the main reason why urban robins they are typically more aggressive than rural birds.
“It should be stressed that physical aggression is a risky behavior for small birds such as robins and is likely to have health consequences.”
When testing urban robins, which already live in noisier habitats, simulated traffic noise did not affect physical aggression levels.
However, birds have adapted to the additional noise by reducing the frequency of their calls.
Lead author Cagla Onsal, who carried out the research during her studies at Koç University, said: ‘Signals are extremely useful because they can deter an intruder without a fight which can be costly for both the land owner and the the intruder, but if the songs cannot be heard by the intruder, the robins may have to resort to physical aggression.
“However, not only does this risk injury, but displays of aggression can also draw attention to predators, such as sparrowhawks.”
The study is published in the journal Behavioral Ecology And Sociobiology.