Formation and Analysis of Long-Term Series of Bird-Population Observations at Key Sites as Way to Study Biodiversity

Studies of 35-year dynamics of the number of bird species and 80-year observations of their arrival on the western macroslope of the Barguzin Ridge have been carried out. A steady decrease in the total abundance of background bird species after 1997–1998 has been revealed. Shifts and cyclic changes in the time of bird arrival have been found. Twenty-six (40.0%) out of 65 species arrived statistically significantly earlier, 7 species (10.8%) arrived later, and 32 species (49.2%) had no statistically significant timing. Correlations have been established between the timing of the first recording of migratory bird species and their local abundance and habitat distribution. Some mechanisms for the formation of the local bird population have been disclosed, including using the redistribution of species breeding density between river valleys and habitats on an altitude profile.