LAUSR

Abstract Month-to-month changes in avian assembages are considerable in forest habitats. In this study such changes were studied by means of the line transect method (eight transect with total length of 77.7 km) in lowland coniferous forest in SW Poland (dominant forest type in Central European Plain), in three consecutive spring months: April, May and June. Shannon’s diversity index varied between 1.31 and 2.25 in particular month, while Simpson’s diversity index and Pielou’s evenness index were almost identical everywhere: H′ = 0.92-0.93 and J′ = 0.74-0.78, respectively. In overall, the differences in mean densities of breeding species between three months on all transects pooled were not statistically significant, as were also not statistically significant such differences on particular transects. Month-to-month variations in densities in all transects pooled were statistically significant in the case of 26 out of 54 species (48.1 %). Month-to-month changes in population densities recorded on transects, only partly conform to the arrival patterns. Two counts, instead of three, would sufficed for precise estimation of bird population densities in Central European lowland pine forests: one count should be conducted in April, to register mainly resident species, and the second one in May to count mainly the migrant species.