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Urban Chaffinches Stayed Aggressive During a Repeated Intrusion

A male common chaffinch perched on a moss-covered stump in Scotland
Research · Behaviour

Male common chaffinches living in an urban part of Istanbul maintained their territorial aggression when researchers repeated a simulated intrusion one day later, whereas males at rural sites reduced their response. The study, published in Ecology and Evolution on 24 February 2026, suggests that city birds may be less flexible in this particular behaviour than their rural counterparts.

The researchers studied the common chaffinch (Fringilla coelebs) because males defend breeding territories and the species occurs in both urban and rural environments. Urbanisation can change food availability, habitat structure and the acoustic setting in which birds communicate. One proposal is that human-made noise masks signals used to assess rivals, potentially making disputes harder to settle through song alone.

Fieldwork took place in Sarıyer, Istanbul, at one urban site and two rural sites. The team tested 23 territorial males: 11 in the city and 12 in the countryside. A speaker was placed inside each territory and played a recording of a male chaffinch song for one minute. Researchers recorded how close the resident male approached, how much time it spent within one and five metres of the speaker, and how many flights it made. Each male received the same playback again after 24 hours, allowing the team to compare both the strength and the consistency of the response.

Urban males stayed aggressive on the second day

Urban and rural males did not differ significantly during the first trial. The contrast emerged on the second day. Rural males became less aggressive, while urban males responded at much the same level as before. Consequently, the urban birds had higher aggression scores than the rural birds during the repeated intrusion. Aggression was also more repeatable among the urban males, and their behaviour varied less from one trial to the next.

Aggression scores of rural and urban male common chaffinches during first and second simulated territorial intrusions
Rural males reduced their aggression during the second simulated intrusion, while urban males did not. Figure 1 from Yelimlieş et al. (2026), Ecology and Evolution, CC BY 4.0.

Noise was not supported as an independent explanation within the city

Across all sites, aggression scores increased with ambient noise. However, noise levels barely overlapped between the urban and rural habitats, and the relationship was not statistically supported when the urban birds were analysed on their own. The authors therefore state that their data cannot establish a strong, habitat-independent effect of noise on aggression. They propose several possibilities for the persistent urban response: noise may hinder recognition of the repeated song, or urban territories may be valuable enough that maintaining a strong defence is worthwhile. Both explanations require further experiments.

The result runs against the expectation that animals successful in cities should show greater behavioural flexibility. Reducing an unnecessary aggressive response could save energy and lower the risk of injury, so a rigid response may carry costs. At the same time, the researchers caution that the sample was small, the birds were not individually ringed, and the study included only one urban location. The work therefore identifies a pattern and a testable question rather than a general rule for city-dwelling chaffinches.

Sources and image credit

  1. Yelimlieş, A., Önsal, Ç., & Akçay, Ç. (2026). Flexibility of territorial aggression in urban and rural chaffinches. Ecology and Evolution, 16(2), e73145. https://doi.org/10.1002/ece3.73145Primary peer-reviewed open-access article first published 24 February 2026 under CC BY 4.0. Repeated simulated territorial intrusions were conducted with 23 male common chaffinches at one urban and two rural sites in Istanbul; rural males reduced aggression on the second trial while urban males did not.

Image: Caroline Legg (cazalegg) — male common chaffinch (Fringilla coelebs), Scotland, photographed 7 December 2020; representative species image, not a bird from the Istanbul study. Source: Wikimedia Commons. · CC BY 2.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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