Urban landscapes as ecological filters: Insights from a Neotropical bird assemblage

To contribute to our growing understanding of the urban ecological filtering process in highly biodiverse regions, we conducted a study on bird species assemblages across the landscape of Medellín and its surrounding areas in the Colombian Andes. Nonurban land cover categories included well-preserved and second-growth forests, exotic-tree plantations, and open areas. Urban areas were categorized into four urbanization levels ranging from 0% to 100% built cover at intervals of 25%. Well-preserved and second-growth forests exhibited the highest bird species richness, followed by open areas, while the 76%-100% urbanization level displayed the lowest richness. Based on either taxonomic or functional composition, the bird assemblages across all urbanization levels resembled open areas. The other nonurban land cover categories shared a lower proportion of bird species with open areas and all urbanization levels, with well-preserved forests showing distinct compositions. These results suggest that bird species inhabiting open areas face a broad urban ecological filtering until reaching a threshold above 75% built cover, while birds inhabiting well-preserved forest face a narrow ecological filtering at the urban edge. Our findings provide insights into urban ecological filtering at the landscape scale and pose significant challenges for urban planners aiming to maintain favorable environmental conditions for highly biodiverse species pools.