BACKGROUND: Urban environments exert strong pressures on animal behavior, leading to altered fear responses to humans. Species with a longer history of urban presence and greater tolerance to urban environments are expected to show reduced fear responses towards humans. Here, we examined whether avian flight initiation distance (a proxy of fear)-the distance at which a bird flees from an approaching human-is associated with a species' timing of urban colonization (i.e., when it has started to breed in urban areas) and with present-day urban tolerance (i.e., how common it is in the city). Unlike previous studies which paired avian fear responses and urbanization timing from different regions, we collected both in the same city (Prague, Czechia), minimizing regional differences in urban history and providing a more rigorous test of the link between urbanization timing and avian fear responses. RESULTS: Using standardized data from 4420 flight initiation distance observations across 68 species, we applied Bayesian phylogenetic mixed models while controlling for ecological and contextual variables. We found that species with a longer urban history (i.e., earlier timing of urban colonization) showed significantly shorter flight initiation distances, suggesting reduced fear responses. In contrast, present-day urban tolerance based on breeding commonness was not related to flight initiation distance variation. CONCLUSIONS: We found that the timing of urban colonization better predicts reduced fear of humans in birds than present-day urban tolerance, emphasizing the role of long-term behavioral filtering and/or selection in shaping urban wildlife behavior. By explicitly separating urbanization time from contemporary urban commonness within a single city and analyzing individual-level fear responses, our study shows that earlier urban colonizers exhibit consistently shorter escape distances, reflecting cumulative long-term processes rather than short-term plasticity alone. These findings highlight the importance of incorporating urban colonization history into behavioral ecology and urban wildlife management frameworks.

Department of Zoology Faculty of Science Palacký University 17 Listopadu 50 Olomouc 77146 Czechia

Faculty of Environmental Sciences Czech University of Life Sciences Prague Kamýcká 129 Prague 16500 Czech Republic

Institute for Advanced Study Technical University of Munich Lichtenbergstraße 2a Garching 85748 Germany

Institute for Environmental Studies Faculty of Science Charles University Benátská 2 Prague 12801 Czechia

TUM School of Life Sciences Ecoclimatology Technical University of Munich Hans Carl von Carlowitz Platz 2 Freising 85354 Germany

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Species' urbanization time but not present urban tolerance predicts avian fear responses towards human