Spatial structure of the population and reproductive success of the bluethroat (Luscinia svecica, Turdidae, Aves) in the south of the Saratov Trans-Volga region

Abstract

The present study was performed in the dry steppe subzone of the Saratov Trans-Volga region during six breeding seasons (years 2010–2015). Habitat features that affected the structure of bluethroat (Luscinia svecica) population were analyzed. The biotopes present in the area investigated differed greatly with regard to the dynamics of environmental conditions during the breeding season. Population density and spatial distribution of nesting territories in each habitat were used to characterize habitat selection, and the breeding productivity was used to assess the result of this selection. Bluethroat population density was always higher in uniformly suitable habitats that provided favorable conditions for nest building and feeding. Part of the population occupied habitats of a lower quality; however, these habitats might be used as “reserve habitats” during breeding seasons characterized by extreme conditions of the environment. Moreover, the contribution of a number of reproductive parameters to the overall breeding productivity was assessed. The present study showed that the starting date and length of fertile period, as well as nest mortality, are the major parameters that determine the variation in breeding productivity between different habitats and seasons. The results are discussed in view of the contributions of population groups to reproduction.