Density and Species Richness of Some Forest Bird Communities in South Sweden

Abstract

Eight forest plots were studied, some of them for five years. Bird community population densities fluctuated from year to year, but the density differences between habitats remained approximately the same. Densities and bird species richness of different forest plots were closely correlated. Both bird community densities and species richness were most successfully predicted from the proportion of the basal tree and shrub area standing dead. Vertical foliage structure and/or number of species of trees and shrubs were minor additional factors. It is suggested that vertical foliage structure is correlated with ecosystem productivity. Food availability is suggested as the ultimate determinant of variations in local bird species richness and community density. The proportion of Turdinae decreased and that of Sylviidae increased with increasing total bird population density. Overall, the bird community structure in different types of forests was similar. The proportion of residents was higher and tropical migrants lower in coniferous than in nearby deciduous forests. Only about 10% of the bird individuals in the coniferous forests were tropical migrants in contrast to about 60% in northeastern North America.