Urbanization reduces shyness and neophobia in a common waterbird

Behavioural plasticity is thought to play a key role in the processes of wildlife urbanization. However, urban behavioural phenotypes may also be shaped by microevolutionary processes, being responsive to unique selection regimes in the urban landscape. Here, we aimed to investigate differentiation of behavioural phenotypes among urban and non-urban populations of a common waterbird, the Eurasian coot Fulica atra. By using field experiments, we tested whether coots from urban and non-urban populations responded differently to a human intruder (shyness) and a novel object (neophobia) at the nest. Our research focused on three coot populations showing different levels of urbanization and different histories of urban colonization. We found that coots from the old urban population required less time to return to the nest and resume incubation following the appearance of a human intruder at the nest, compared to non-urban coots. Similarly, the probability of returning to the nest and resuming incubation upon exposure to a novel object at the nest was higher in old urban population than in non-urban coots. These results provided robust experimental evidence for the reduction of shyness and neophobia in the old, long-established urban coot population. Moreover, birds from a new urban population showed intermediate behavioural reactions, suggesting that urban behavioural phenotypes develop gradually since the urban colonization event. While still requiring experimental validation (e.g., through common garden experiments), our results suggest that both short-term effects of phenotypic plasticity and long-term effects of microevolutionary adaptations may contribute to the development of optimal urban behavioural phenotypes.

Significance statement Urban life is known to promote the emergence of remarkable behavioural phenotypes in different groups of animals, including birds. Here, we provide experimental evidence for reduced shyness and neophobia in urban Eurasian coots Fulica atra during the breeding season. We also show that the expression of urban behavioural phenotypes was stronger in the old than new urban population, indicating that it increased with time from the urban colonization event. Although behavioural plasticity may rapidly produce differences in behaviour at the early stages of urbanization processes, we argue that long-term microevolutionary processes may gradually reinforce this differentiation. Our study provides novel insights into the mechanisms responsible for the behavioural differentiation of urban and non-urban animals, enhancing our understanding of how animals modulate their behaviour during the Anthropocene.