ИСТИНА

Since early 1980-s, “Parus” program coordinates winter land bird census on an extensive network of study sites across European part of Russia. The territory of about 3,3 million km2 was divided into 5 forest subzones, with 3–4 longitudinal sectors in each. Volunteer observers make annual censuses in one or several sites in all these parts, conducting censuses on at least 20-km route for each typical habitat. We analyzed winter abundance trends for 14 most abundant species over the period 1987–2017. Using rtrim package for R, we estimated missing data for all study sites. For each sector of the territory, we averaged winter population numbers, considering the area of forest habitats appropriate for each species. These assessments, divided by numbers of study sites in each sector, were used as weight coefficients in trends calculations. We obtained population indices and calculated trend parameters for the whole study period, as well as before and after 2001. None of the species had positive trends in any period. During 31 years, three species showed stable trends, and 8 of them demonstrated significant population decline, in many cases accelerated since 2000-s. The decline was most pronounced in Goldcrest (Regulus regulus), Crested Tit (Lophophanes cristatus) and Willow Tit (Poecile montanus). For most of the studied species, these tendencies probably reflected the changes in tree composition, caused by intense logging in the taiga zone. It had resulted in a dramatic decrease of old coniferous forests area, which was substituted with young, mostly deciduous stands. Other factors such as climate change could also play a role.