Factors affecting bird species diversity on a local scale: a case study of a mosaic landscape in Southern Poland

The main objective of this paper was to investigate factors that affect bird species diversity at local spatial scales including the role of habitat heterogeneity. The studies were carried out in a mosaic landscape of southern Poland, in habitat fragments, each described by variables which characterised the size of the plot and its spatial structure, including vegetation. A species diversity index was then calculated for each plot using Shannon-Wiener index, based on count of nesting birds obtained through territory mapping method. Correspondence analysis (CA) was then used to illustrate relationships between groups of plots of different scopes of species diversity and the measured characteristics of the plots. The high diversity among birds was found to be primarily connected with an increase in the proportion of old forest, whereas the diversity decreased with an increase in the proportion of ‘farmland’ (including meadows and pastures). Other significant effects on the changes in species diversity were exerted by the degree of density in the herb layer and the tree canopy layer, as well as by the presence of wetlands. The localscale inertia in the heterogeneous-type habitats results primarily from the differences in quality and structure of the plot, which reflect their position between the ‘forest’ – ‘non-forest’ gradient. In the studied range of sizes (0.2–40 ha), the size of a given plot is of lesser significance than that of the vegetation structure. All the variables which represent potential effects upon the local-scale diversity of birds, and the suitability of CA are discussed against the background of the results of this study and available literature data.