EFFECTS OF URBANIZATION ON THE BREEDING BIRD SPECIES RICHNESS IN FINLAND - A BIOGEOGRAPHICAL COMPARISON

Cities represent the extreme of human-modified environments, with only remnants of the original habitats present. To study how increasing ur banization 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 urba n 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 e stimated number of breeding bird species decreased with urbanization. The highest species richness was found in the countryside (21.8 specie s in a 50-pair sample) and the lowest in the large city center (7.4 sp p.). This finding supports the widely accepted hypothesis that moderat e 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 point s to the important role of trees and shrubs as shelter, and as nesting and feeding places. The species richness was similar at different lat itudes, when the level of urbanization was the same. The great product ivity (amount of food) and high predictability of resources (food avai lable throughout the year) in the urban habitats may explain why the s pecies richness does not decrease northwards in the urban environments .