Green space area and type affect bird communities in a South-eastern European city

Urbanization decreases the species richness and results in the homogenization of bird communities. Bird species are important indicator species for biodiversity and reflect the habitat quality of urban forests and other green spaces. In this study we investigated the key drivers that influence bird communities in urban forests and green spaces in the Southeastern European city of Ljubljana, Slovenia. We were interested in how the number of species, species dissimilarity and indicator species are affected by the type of green space (urban forest vs park), area of green space and type of urbanization (urban vs peri-urban areas). We sampled birds twice in 2012 in 39 standardized point counts across Ljubljana. We found that the abundance was influenced by the area of the green space. Species dissimilarity and species turnover are affected by the area and type of green space. Interestingly, the analysis showed that the species composition of peri-urban areas was similar to that of urban areas. Indicator species were found for all environmental variables. On the basis of the results, we suggest the strategy that would increase the diversity of birds and increase the stability of their populations in urban areas. Urban planners should encourage 1) both forests and parks since they harbour different species of birds, 2) larger green spaces since larger areas have species that are more typical of larger areas and 3) a mosaic of a larger number of smaller forest remnants combined with larger forest complex serving as source areas.