Changes in the Fauna and Distribution of Birds of the Forest-Steppe Trans-Urals in the Late 20th to Early 21st Centuries Under the Influence of Natural and Anthropogenic Factors

The distribution of birds in the West Siberian plain in the western part of the forest-steppe zone (bound east by the Ishim River) is very dynamic. Just since the beginning of this century, 17 new breeding species have been discovered in this region. Most of them (76%) are representatives of the Tropical group (five species) dispersing from the south, as well as the Nomadic (5) and the European (3) types of fauna coming from the south and the west; three species belong to the Chinese type of fauna and one belongs to the Siberian type. Another new species from the Tropical group was recorded as breeding in the last decade of the previous century. The distribution ranges of all six representatives of the Tropical group and two species of the Nomadic fauna associated with aquatic habitats have expanded northward most over the past 40 years (for 500–600 km). A powerful wave of their dispersal in the forest-steppe occurred during the years of maximum filling of water reservoirs in the early 2000s. At the same time, despite the cyclical dynamics of the water level, cyclical processes in the changes of the distribution of limnophile birds are not expressed (analysis of century-long faunal lists shows the cyclical nature of the distribution of no more than 2–3 such species). It is assumed that against the background of intense climate warming most bird species, primarily limnophiles, are not simp-ly redistributing individuals within the ranges, but are expanding their ranges northward, and that expansion will continue in the future. The anthropogenic impact on the regional avifauna is mainly caused by the consequences of the economic crisis in agriculture. In recent decades, it has been much less obvious than the na-tural impact.