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

Abstract

Cities represent the extreme of human-modified environments, with only remnants of the original habitats present. To study how increasing urbanization affects breeding bird richness ; we 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. The breeding birds were censused using the territory mapping or study plot method. The estimated number ofbreeding bird species decreased with urbanization . The highest species richness was found in the countryside (21 .8 species in a 50-pair sample) and the lowest in the large city center (7 .4 spp.) . This finding supports the widely accepted 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.) . This result points to the important role of trees and shrubs as shelter, and as nesting and feeding places. The 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 the urban habitats may explain why the species richness does not decrease northwards in the urban environments.