Abundance and demographic structure of the great bustard (<i>Otis tarda</i>) (Otididae, Aves) population at lek areas in the Saratov and Volgograd Trans-Volga region

Abstract

The results of our studies of the great bustard population in the Saratov and Volgograd Trans-Volga region are presented. For the first time in this territory, censuses of the numbers of bustards were carried out in their lek areas in the spring for 3 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 compare them with those obtained during autumn population counts. In our opinion, as a result of agriculture intensification, 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 protection measures, this has led to a reduction in the numbers of birds in the Saratov Trans-Volga region by almost 10 times over 20 years. This trend is observed throughout almost the entire world range of the great bustard, where there are no long-term effective measures aimed at preserving the natural habitats of the species. In the Trans-Volga region, the number of lek areas has decreased by approx. 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 significantly decreased. 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 whose clutches have been preserved, have the problem of acute food shortage after their chicks hatched, which also leads to elimination of some part of the broods.