Data on bird abundance in urban woodlands in 32 Swedish cities

The expansion of urban areas is increasingly contributing to biodiversity
declines. Several studies have analyzed the effect of increasing
urbanization on bird diversity, but few have differentiated effects of
urban landscapes (matrix) from changes in focal habitat quality at
multiple spatial scales. In this study we analyzed the effect of
urbanization on bird communities in individual (local scale) and across
multiple (regional scale) cities while controlling for the quality of
sampled natural habitats. We conducted bird point counts and habitat
quality mapping of trees, dead wood and shrubs in 459 forest remnants
along an urbanization gradient in 32 cities in Sweden. We then analyzed
how the degree of urbanization affected species richness of
woodland-breeding bird and red-listed bird species at a regional and local
scale. We also analyzed how urbanization affected beta-diversity and
dissimilarity between communities at the different spatial scales, and if
dissimilarities in species communities along the urbanization gradient
were driven by species nestedness or turnover. We found that urbanization
decreased species richness, and the number of red-listed species, at both
the regional and local scale. Dissimilarities in woodland-breeding bird
communities among urban, semi-urban and peri-urban areas at the local
scale were particularly due to turnover, and at the regional scale to
nestedness. Since there was no difference in habitat quality among
woodlands across the urbanization gradient, we conclude that landscape
urbanization systematically causes poorer and more homogeneous bird
communities. However, despite that natural habitats in cities contribute
less to the regional diversity, they are critical to maintain the local
bird communities of individual cities and their surroundings.