Homogenisation processes and local effects on avifaunal composition in Italian towns

We tested whether urbanization homogenizes breeding bird communities. We compared the similarity of breeding bird communities among different urban sectors: town centres, inner periphery, outer periphery and scarcely built areas, at regional and local scale in 26 Italian towns. If urbanization causes homogenisation, the similarity of bird communities between different towns should be higher in the more urbanised sectors. We obtained data on presence of bird species in each square of the grid of urban atlases. We used the frequency of each species in each urban sector to calculate a similarity index. The similarity of the avifauna between towns was lowest in scarcely built areas and highest in the inner periphery. For each urban sector, the similarity indices between towns were negatively correlated with differences in both latitude and altitude between towns. The values of regression coefficient increased from the centre to the less urbanised sectors although the scarcely built area did not show the highest values. The frequency of a specialist group, the Mediterranean species, was negatively correlated with latitude only in the least urbanised sector. These results indicate that urbanization promotes homogenisation of biological communities. However, the similarity of avifauna between sectors in each town was higher than the similarity between different towns for the same sector. These and other findings suggest that local factors play an important role for the composition of urban bird communities.