Why traffic noise makes robins more aggressive

By Mark Waghorn via SWNS

Traffic noise is making rural robins more aggressive, according to new research.

The fiercely territorial birds are getting physically confrontational because their song can't be heard above the din.

They rely on signals, both visual and acoustic, to keep out other individuals - and change behavior when threatened.

It has implications for animal conservation and environmental regeneration projects, scientists say.

Senior author Dr. Caglar Akcay, of Anglia Ruskin University, explained: "We know human activity can have a significant impact on the long-term social behavior of wildlife.

"Our results show human-produced noise can have a range of effects on robins, depending on the habitat they live in."

The international team measured aggression toward an intruder by using a 3D model - accompanied by recordings of robin songs. Traffic noise was added through a speaker.

Dr. Akcay 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, and we believe this is because the noise is interfering with their communication."

It adds to evidence human activities are preventing birds from developing normal social behavior and keeping the peace - and even reproducing.

The noise stops the sharing of crucial information. Aggressive communication is common - and birds may mistake the signals.

What is more, fights draw attention - making robins more vulnerable to predatory crows, jays and sparrowhawks.

Birds already face an array of human-made dangers, from pesticides and intensive farming to shooting and poisoning. But noise had often been overlooked, the paper in Biology Letters found.

A spokesperson for the RSPB said: “Everyone is becoming increasingly concerned that nature is in crisis in the UK, with one in 10 of our wildlife species at threat of extinction.

"Many of our birds’ populations are already facing a serious crisis as a result of habitat loss, climate change and other human activities.

“This report is a good reminder that the way we live and our lifestyle has an impact on our natural world and that we need to protect our natural world if we want to let nature sing.”

The research does not have clear implications for human health, although excessive noise can damage children’s ability to learn and causes stress among adults.

Dr. Akcay 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.

"It should be stressed that physical aggression is a risky behavior for small birds like robins and is likely to have health consequences."

The purpose of birdsong is twofold – to attract mates and defend territory. Dr. Akcay and colleagues analyzed male European robins living in both urban and rural areas.

As well as adapting their sounds to ward off rivals, robins adopt specific visual displays during territorial interactions.

These include swaying and displaying the red feathers on their neck, as well as moving closer to their opponent and attempting to chase it away.

As expected, the urban robins typically displayed more physical aggression than rural counterparts during interactions with the simulated intruder.

But the latter became more aggressive with traffic noise. Physical displays of territoriality increase because it interferes with signaling behavior using songs.

The simulated traffic sounds did not affect levels of physical aggression in the urban robins as they are used to noisier habitats. But they adapted by reducing call rates.

It is believed they have learned to 'sit out' temporary increases in noise. Rural robins instead compensate with increased physical aggression.

Added lead author Cagla Onsal, a graduate student at Koc University, Turkey: "Signals are extremely useful because they can deter an intruder without a fight that may be costly to both the territory owner and the intruder.

"But if the songs can't be heard by the intruder the robins may have to resort to physical aggression.

"However, this not only risks injury but displays of aggression can also draw attention to predators, such as sparrowhawks."

Birds already face an array of human-made dangers, from pesticides and intensive farming to shooting and poisoning.

Noise had often been overlooked. The study in Behavioral Ecology and Sociobiology was funded by the British Ornithologists' Union.