Abstract
Urbanization is a worldwide phenomenon converting natural habitats into new artificial ones. Environmental conditions associated with urbanization represent great challenges for wildlife. Behaviour and stress tolerance are considered of major importance in the adaptation to novel urban habitats and numerous studies already reported behavioural and stress response phenotypes associated with urbanization, often suggesting they represented adaptations, while rarely demonstrating it.The main goal of this study was to test the adaptive nature of urban shifts in behavioural and stress-related traits, and by adaptive we mean phenotypic change favouring traits in the same direction as selection.Using seven years of monitoring of urban and forest great tits, we first tested for differences in exploratory behaviour, aggressiveness and breath rate, between both habitats. Second, we performed habitat-specific analyses of selection on the three former traits using (1) reproductive success and (2) survival estimated via capture-mark-recapture models, as fitness estimates, to determine whether shifts in these behavioural and stress-related traits were aligned with patterns of ongoing selection. We found that urban birds displayed higher exploratory behaviour and aggressiveness, and higher breath rate, compared to forest birds. Selection analyses overall revealed that these shifts were not adaptive and could even be maladaptive. In particular, higher handling aggression and higher