Angry Birds: Rural Robins Get ‘Road Rage’ When Exposed To Traffic Noise

Human activities, such as traffic noises and other forms of noise pollution, can have significant impacts on the long-term social behaviors of wildlife

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A recently published study has found that human-made traffic noises are linked to increased physical aggression in rural European robins, Erithacus rubecula. Surprisingly, their urban-dwelling relatives show no such response to traffic noises. Why?

Robins are fiercely territorial

The European robin, more commonly known as the robin or robin redbreast, is formally classified into the Old World flycatcher family. This small insectivorous passerine is common and widespread throughout Europe, western Asia and some parts of northern Africa, where it lives in woodlands and parks. It is seasonally migratory in northern Europe, but in the southern parts of its range, this bird tends to stay put. Males and females look identical, whereas juveniles lack the iconic red breast but instead, have golden spots sprinkled uniformly over their honey-brown plumage.

The endearing appearance and small size of robins conceals an unexpected trait: they are quite hawkish. These songbirds aggressively defend their territories from any and all who dare to encroach upon it. Their territorial defense is initially trumpeted with loud, continuous song and, if the invader doesn’t get the hint, the territory-holder then uses a variety of visual displays, such as swaying side-to-side, displaying the brilliance of their red neck feathers, pointing their beak forward, drooping their wings and pricking up their tail, or advancing very close to their target, to indicate the growing threat level to the intruder and to scare him into fleeing. If none of these behaviors have the desired effect, territorial disputes then escalate to knock-down drag-out fights that can result in the death of one or both combatants.

Clearly, a fight to the death is not an evolutionarily stable strategy, but noise pollution appears to play a major role in increased physical aggression seen in rural robins — but not in urban robins. Why?

Raging Rural Robins

One way to approach this question is to compare the behaviors of male European robins living in both urban and rural areas. An international team of scientists recorded urban robins’ behaviors and found they adapted to traffic noise pollution by waiting for lulls in the traffic noisescape so they could produce territorial defense songs and calls with greater effect.

In contrast, the normally more peaceful rural robins hadn’t learned that traffic noises vary in intensity, so they instead became increasingly violent whilst traffic noises were played.

“We know that human activity can have a significant impact on the long-term social behavior of wildlife, and our results show that human-produced noise can have a range of effects on robins, depending on the habitat they live in”, said senior author of the study, Çağlar Akçay, a senior lecturer in behavioral ecology at Anglia Ruskin University.

The authors of this study tested the birds by setting up a 3D-printed plastic model of a robin as a simulated intruder in another robin’s territory at two locations: an urban park in Istanbul close to a road, and a quiet wooded area outside the city. The model played recordings of robin songs, which was guaranteed to attract the territory-holder’s attention. Then, the researchers added traffic noise through a separate speaker nearby.

“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”, Dr Akçay said.

The researchers found that urban robins were generally more physically aggressive than rural robins.

“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”, Dr Akçay noted.

When recordings of traffic noises were played, the rural robins surprised the researchers by becoming much more physically aggressive than urban robins. The scientists think that physical displays of territoriality increase because loud traffic noises interfere with the robins’ territorial defense song signals so “a robust, physical approach is more often necessary to discourage other males from muscling in on their territory.”

“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”, Dr Akçay said.

“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”, said the study’s lead author, Çağla Önsal, who was a graduate student in Cognitive Psychology at Koç University when this study was conducted. “[B]ut if the songs can’t be heard by the intruder, the robins may have to resort to physical aggression.”

Increased physical aggression could attract the attention of a predator, like the neighborhood cat hiding in the bushes.

“It should be stressed that physical aggression is a risky behavior for small birds like robins and is likely to have health consequences”, Dr Akçay said.

Source:

Çağla Önsal, Alper Yelimlieş, and Çağlar Akçay (2022). Aggression and multi-modal signaling in noise in a common urban songbird, Behavioral Ecology and Sociobiology 76:102 | doi:10.1007/s00265-022-03207-4


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