# Flexibility of Territorial Aggression in Urban and Rural Chaffinches

## TL;DR

Urban chaffinches show less flexible territorial aggression compared to rural ones, and aggression increases with ambient noise.

## Contribution

Contrary to expectations, urban chaffinches showed less behavioral flexibility in aggression despite higher noise levels.

## Key findings

- Urban chaffinches were less flexible in territorial aggression compared to rural chaffinches.
- Aggression levels increased with higher ambient noise levels in both urban and rural chaffinches.
- Rural chaffinches decreased aggression in repeated trials, while urban chaffinches did not.

## Abstract

Rapid environmental change due to urbanization poses novel challenges to animals. Behavioral change and individual plasticity are generally hypothesized to be the key to adapting to these challenges. One commonly observed behavioral change is higher observed aggression levels in urban animals, perhaps because anthropogenic noise disrupts effective acoustic communication during conflicts, leading to greater use of physical aggression. We investigated the hypothesis that urban noise drives aggression by performing repeated simulated territorial intrusion experiments on rural and urban chaffinches (
Fringilla coelebs
). We expected urban chaffinches to be more aggressive, change their aggression levels more between trials, and for aggression to increase with noise levels, irrespective of the habitat. We found that while aggression did not differ between habitats in the initial trial, rural chaffinches decreased their aggression level in the second trial and thus were less aggressive than the urban chaffinches, which did not change their response. That is, urban birds were less flexible in responding to an intruder than rural birds, contrary to previous findings in other songbirds. Moreover, aggression levels correlated positively with ambient noise levels. Given our small sample size and lack of spatial replicates, our results should be interpreted with caution. Nevertheless, as a lack of flexibility in aggression is potentially costly, our results highlight the importance of studying the plasticity in aggressive behavior in human‐impacted landscapes.

Behavioral flexibility of urban animals may allow them to adapt to rapid environmental change. We tested whether urban chaffinches are more flexible in territorial aggression than their rural counterparts and whether changes in territorial aggression are related to anthropogenic noise. Contrary to our expectations, we found that urban chaffinches were less flexible in aggression; however, aggression increased with increasing ambient noise levels, irrespective of the habitat.