Wings over the city: avian and butterfly diversity across a gradient of anthropogenic disturbance

In the last decades, interest in monitoring and quantifying biodiversity in human-modified landscapes ha increased, as anthropogenic disturbance is recognized as a major driver of biodiversity loss. However, green spaces within disturbed environments can sometimes serve as critical refuges for wildlife. In this study, we collected and analyzed data on bird and butterfly communities across a gradient of anthropogenic disturbance in Bologna (Italy) encompassing urban, agricultural and semi-natural contexts. We found the highest species richness and diversity for both taxa in peri-urban areas with natural and semi-natural habitats, while the dense built-up areas supported fewer, mostly generalist species. Intermediate zones, including parks and gardens, acted as ecological filters, hosting both specialist and generalist species, while agricultural areas favoured birds likely due to their greater vagility, but not butterflies, whose communities showed sharper compositional shifts. Finally, we found that both continuous urban cover, discontinuous high-density urban areas, distance to streets, and wood coverage were the main drivers of α and β diversity in our target groups. Our findings highlighted the importance of habitat heterogeneity and continuity with the natural areas surrounding the city in sustaining biodiversity under anthropogenic disturbance. The integrated analysis of two bioindicator groups along a disturbance gradient produced original and transferable results, offering a replicable model for ecological studies and urban planning in similar contexts.