Structure and factors of forest birds diversity forming in the Ishim river area (Russia)
The paper studies the relationship between specific parameters of habitats (the forest area along the route, the average age of the forest, the closure of the crowns, the condition of the crowns, the type of anthropogenic impact, the stage of vegetative succession, the wetting of the forest), the abundance of birds, Shannon and Simpson's indices of the species diversity of forest ornithocenosis. This study is based on the materials of field bird records conducted in the seasons of 2014-2016 on 28 permanent routes in the forest habitats of the Ishim River area (Russia). A statistically significant effect of the anthropogenic impact on the Shannon diversity index and the significant influence of the plant succession stage on Shannon's species diversity index and the abundance of birds have been established by the method of one-way analysis of variance using the nonparametric Kraskel-Wallis's criterion. It is shown that the maximum value of Shannon's index of variety is characteristic for the ornithocenosis of recreational forests; the one close to the maximum is in forests in which grazing is carried out. In the course of plant succession, there is initially an insignificant increase in the total abundance of birds, then a significant decrease in it, as well as a sharp decrease of Shannon's diversity index. The obtained results show that the anthropogenic load in form of cattle grazing and recreation conditions an increase in forest habitats' heterogeneity and thereby contributes to an increase in bird species diversity.