Flight initiation distance and bird tolerance to humans in rural and urban habitats

Urbanization induces homogenization and changes the behavioural patterns of various bird species, thereby facilitating coexistence and prompting adaptations to disturbances in urban environments. However, there is limited research on the influence of how urbanization affects bird tolerance towards humans, especially in developing sub-tropical regions such as Nepal, which is undergoing rapid unplanned urbanization. This study identified the flight initiation distance (FID) as a proxy for assessing bird tolerance. We focused on evaluating the human tolerance levels of 33 bird species using their FIDs in urban and rural habitats within Kathmandu Valley, a rapidly urbanizing city in South Asia. We found higher tolerance in urban birds than in their rural conspecifics, which varies mainly with dietary guild and season. The positive impact on FID was associated with time of the day and body size, while a negative association was observed with flock size, mean population density of humans and interaction between body size and elevation. Our study highlights the increased tolerance level of birds in urban areas, probably owing to habituation, and emphasizes the imperative need to investigate the potential adverse effect on urban bird population owing to this increased tolerance level.