Spatial similarity of urban bird communities:: a multiscale approach

Aim Human land use, especially urbanization, might homogenize the world's biota. The objective of this study is to find out if urbanization homogenizes wintering bird communities, and if habitat type affects the spatial variation of urban bird communities across spatial scales. Location We compared the quantitative similarity of winter bird communities between town centres, apartment block areas and single-family house areas across regional and local scales in five towns in northern Finland. Methods The wintering birds were surveyed using a single-visit study plot (30 ha) method in January and February 2001. The validity of single-visit and single-year data was confirmed by using data from several-visit surveys and multi-year data set. The level of urbanization was measured according to the number of inhabitants and general structure of the habitat. Results Temporal variability in species richness and total number of individuals was low, both between winters and within winter. Bird community similarity between different habitat types within a single town was about the same as that in similar habitats in different towns. At the regional scale, bird community similarity between town centres (30%) was lower than between areas of apartment blocks (54%) or between areas of single-family houses (54%). We detected a threshold point between towns of 35,000 and 105,000 inhabitants and between town sizes of 5.0-8.5 km in diameter where human impact causes marked changes in bird community structure. At the local scale, bird community similarity level between apartment block areas (49%) and single-family house areas (62%) were about the same. Passer domesticus, Parus major and Pica pica dominated the bird communities in residential areas. Different habitat factors affected bird species abundances on the local and regional scales. Conclusions Urbanization cannot be seen as a process that monotonically increases the similarity of bird communities. Our results indicate that the similarity between urban bird communities is dependent on the size of the town, location of the study site within the town and especially the local habitat structure. Because different habitat factors affected bird species abundances, it is difficult to extrapolate bird-habitat relationships derived from one scale to other scales. In wintertime, single-family house areas are important biodiversity hotspots in cities. Therefore, it is especially important to understand the factors affecting the occurrence of birds in the single-family house area in order to maintain or even increase diversity on winter birds in other urban habitats.