Abundance and Demographic Structure of the Great Bustard (Otis tarda) (Otididae, Aves) Population at Lek Areas in the Saratov and Volgograd Trans-Volga Region

The results of our studies of the great bustard population in the Saratov and Volgograd Trans-Volga regions are presented. For the first time on this territory, censuses of the numbers of bustards were carried out in their lek areas in the spring over a period of three years. This made it possible to obtain more reliable data on the numbers of individuals of this species, as well as on the demographic structure in the model area, and to compare them with those obtained during fall population counts. In our opinion, as a result of intensification of agriculture, the nesting habitats of the bustard have been sharply reduced, which was caused by changes in the structure of crop areas and the massive use of pesticides. In the absence of necessary protective measures, this has led to a reduction in the numbers of birds in the Saratov Trans-Volga region by almost ten times over 20 years. This trend is observed throughout almost the entire world range of the great bustard, where no long-term effective measures aimed at preserving the natural habitats of the species are taken. In the Trans-Volga region, the number of lek areas has decreased by approximately half and the numbers of individuals of the species in the remaining leks have decreased. The demographic structure of the bustard population when studied in lek areas shows a significant predominance of males over females, which contradicts the stability of the population. Due to the reduction in the number of habitats suitable for bustards to nest, the success of their reproduction has decreased significantly. Spring treatment of crop areas with pesticides by ground and aerial methods coincides with the nesting period of birds, which is a powerful factor of disturbance and leads to the loss of clutches. Females the clutches of which have been preserved have the problem of acute food shortage after their chicks hatch, which also leads to elimination of some part of the broods.