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The article deals with the main results of a long-term study of birds in the Barguzin State Nature Biosphere Reserve (Russia). Phenological observations of the bird spring arrival have been carried out from 1938 to 2020. Monitoring of bird communities has been carried out from 1984 to 2020 on permanent counting routes in the valleys of three rivers in the area from the Lake Baikal coast to the highlands of the Barguzin Range (460–1700 m a.s.l.). We detected shifts and cyclical changes in the timing of the bird arrival and revealed a steady decrease in the abundance of the bird population after 1997–1998. The long-term series of observations (taking into account of model bird groups) made it possible to identify some responses of the biota to climatic changes in the Lake Baikal Region. Twenty-six species (40.0%) began to arrive in spring statistically significantly earlier, seven species (10.8%) significantly later, and for 32 species (49.2%) the arrival timing did not change statistically significantly. In contrary to Europe and North America, in the Baikal Region, the proportion of distant migrants in the group of early arriving bird species is higher than in the group of nearby migrants. We suggest that these differences may be associated with different wintering areas of long-distance migrants (species of the Baikal Region winter in South and Southeast Asia in contrast to African wintering areas of European birds). In the Baikal Region, the periods of high and low abundance in background species populations are probably associated with the passage of wet and dry phases of a long climatic cycle. We have identified positive trends in long-term changes in abundance for seven background species (14.0%), and a steady decline in abundance for 17 species (34.0%). In addition, we noted an equal ratio of species with a positive and negative trend in native species abundance. Negative trends of changes in the number of distant and nearby migrants prevailed over positive (increase) trends. So, we found 14 species with negative and four species with positive trends. An increase in the duration of observations makes it possible to give a more reliable assessment of processes in population dynamics, and identify mechanisms of the influence of meteorological and phenological factors on the dynamics of the abundance of bird species. This makes it possible to predict some biota responses to long-term climate changes in the absence of anthropogenic transformations of the natural environment.

A decrease in the number and the timing shift of the bird arrival in the North-Eastern Baikal Region