Banik M. Chats (Aves: Saxicola) of the North-eastern Ukraine: distribution, biology, behaviour

The European Stonechat (Saxicola rubicola) rapidly colonised vast areas in the Ukraine in the twentieth century. As a result, a zone of sympatry with far more numerous species, the Whinchat (S. rubetra), was formed in the North-eastern Ukraine in 1960s – 1980s. The key questions aroused about what are the causes for the expansion of the range of the European Stonechat and which aspects of the biology of both species facilitate their coexistence in bird communities. The results of the research indicate that it became possible owing to the almost complete separation of the main phases of the breeding cycle of the species, the dissimilar requirements in the size of the breeding territories, the absence of interspecific territoriality etc. The abundance of the Whinchat is several times higher than that of the European Stonechat in all studied habitats. The level of abundance of both species in chalk steppe clearly depends on different factors and the changes of the numbers are asynchronous and not unidirectional. The expansion capability of the European Stonechat is probably enhanced by different behavioural strategies in the young birds originated from the first-and the second clutch broods. The observed waves of expansion were caused by the climate fluctuations which favour the survival of the birds at the critical time of the southward migration. The causes of the expansion were also favourable changes in the habitat structure following flood-plain drainage.