Effects of urbanization on the breeding bird species richness in Finland: a biogeographical comparison

The authors compiled literature data on bird assemblages at five different levels of urbanization (forest, countryside, village, small and large city centers) and along an urban gradient (park, residential area and city center in different towns) in the three ornithogeographical zones in Finland. Estimated number of breeding bird species decreased with urbanization. Highest species richness was found in the countryside (21.8 species in 50-pair sample), the lowest in the large city center (7.4 spp.). Data support the hypothesis that moderate disturbance will increase biotic diversity. The estimated number of breeding bird species was lower in the city centers (6.8 species in a 25-pair sample) than in the urban parks (12.1 spp.), pointing to the important role of trees and shrubs as shelter, and as nesting and feeding places. Species richness was similar at different latitudes, when the level of urbanization was the same. The great productivity (amount of food) and high predictability of resources (food available throughout the year) in urban habitats may explain why the species richness does not decrease northwards in the urban environments. -from Authors