Bird community responses to urbanization and vegetation parameters across the city of Salzburg, Austria

Abstract

Urbanization continues to be a major threat to biodiversity. The knowledge of local and site characteristics that influence species diversity within cities is of importance to design and manage urban spaces that promote biodiversity and ecosystem services. While the characteristics of urban green spaces for biodiversity have been studied in detail, the urban matrix has received less attention. We, therefore, studied the role of sampling site and local-scale parameters at different urbanization intensities on bird and tree communities during the breeding season across the city of Salzburg encompassing the heterogeneity of the urban landscape. We found more exotic than native tree species, however areas with many trees, were dominated by native tree species. Although building cover negatively related to bird species richness at all scales, bird species richness increased with the amount of grass cover, the number of trees and the number of native tree species at the smallest, i.e. sampling site, scale. Building cover and the number of trees in a sampling site also influenced bird community composition. At larger scales, land cover (i.e., building cover and green urban area) was more strongly related to bird community composition than sampling site characteristics. Relationships with community composition can partly be explained by species-specific responses as the occurrence of different species was associated with different sampling site characteristics. Our study shows the importance of unsealed soil, i.e. grass cover, and native trees on bird communities within cities, but different species may require different configurations of these habitat parameters. Furthermore, also within the urban matrix site characteristics can promote avian diversity even in areas with high building cover.

Supplementary information: The online version contains supplementary material available at 10.1007/s11252-025-01738-y.

Keywords: Bird community; Bird species richness; Tree species richness; Urban ecology; Urban matrix.

Fig. 1

Map of the city of Salzburg showing the 48 sampling points of the study, created with QGIS 3.22.11. Data provided by OpenStreetMap. The city border (black line) was prepared using European Union’s Copernicus Land Monitoring Service (https://land.copernicus.eu/local/urban-atlas/urban-atlas-2018)

Fig. 2

Non-metric multidimensional scaling (NMDS) plot of tree community composition at the different sampling sites (black dots) in Salzburg (Sørensen dissimilarity, stress = 0.15, k = 3). Exotic tree species or domesticated varieties are shown as red triangles, native tree species are shown as purple triangles. The number of trees recorded at a 50-m scale was the only environmental variable that had a significant influence on tree composition in the permanova (Table 1) and is plotted as an arrow

Fig. 3

The relationship between A) building cover (in %), B) grass cover (in %), C) the number of trees and D) the number of tree species (the number of exotic tree species in red and native tree species in purple) in a 50-m radius and bird species richness in Salzburg. The relationship between the number of exotic tree species and bird species richness was not significant (Table 2) and is thus shown as a dashed line

Fig. 4

Non-metric multidimensional scaling (NMDS) plot of bird community composition at the different sampling sites (black dots) in Salzburg (Sørensen dissimilarity, stress = 0.15, k = 3). Species with woodlands and forests as original habitats are coloured in green, those with other habitats (grassland, human-modified, rock, shrubland and wetland habitats) are coloured in blue. Bird species names were moved slightly after plotting to avoid overlap. The environmental variables that had a significant relationship with bird composition in the permanova (Table 1) are plotted as arrows

Fig. 5

The relationship between A, B) building cover (in %), C, D) the number of trees, E–F) the number of exotic tree species, G-I) the number of native tree species in a 50-m radius around the recording point and the presence of specific bird species in Salzburg