Distribution and structure of bird assemblage in Northern Eurasia in the first half of summer

To reveal features of the distribution of birds in Northern Eurasia, the results of surveys carried out in the period from 1880 to 2019 (with interruptions and mainly since 1960) averaged over the first half of the summer (May 16–July 15) were analyzed. 354 researchers participated in the collection of material (for 110 years). Data processing was carried out using multivariate statistics methods, including cluster analysis and linear qualitative approximation of connection matrices. The classification of bird species by their distribution accounts for 42% of its similarity. The information content of representations decreased by 10–15% only (by 12% on average) with twice as many species analyzed, a significantly larger number of surveyed habitats and the area of the studied territory (as compared to the previously surveyed East European and West Siberian Plains and Altai). This level of explanation can be considered satisfactory (the correlation coefficient is 0.65). The summer distribution of bird species, as well as the heterogeneity of their distribution as a whole, is determined by changes in the hydrothermal regime in the zonal-belt and provincial aspects. The heat-to-moisture ratio determines the type of vegetation and its productivity both on land and in aquatic and semiaquatic habitats. The specificity of the vegetation type in territories and water areas, taking into account anthropogenic transformation, coincides with the heterogeneity of the bird distribution and the formation of ornithocomplexes as a whole. With the division of geographical space into zones, subzones, and especially physiographic countries, the variability in the distribution of birds and their communities is associated to a lesser extent, occupying the second and third places in the hierarchy of significance, respectively.