TO IMPROVING RANGES OF SIBLING SPECIES MI CROTUS-ARVALIS AND MICROTUS-ROSSIAMERIDIONALIS (RODENTIA, CRICETIDAE) IN REGION BETWEEN THE LOWERVOLGA AND TURGAI RIVERS

At present the exact pattern of distribution of two related species Mi crotus arvalis and M. rossiaemeridionalis on the vast territory of the superspecies range in adjacent regions of eastern Europe and north-we stern Asia remains unknown. Therefore the basic goal of the research w as to obtain new data on geographic ranges and habitat preferences of these two species in this region. The route of the expedition was 5 km long and covered the area of about 400 thousand sq. km situated in th e steppe, semidesert and desert zones between the lower part of the Vo lga River (Europe, Russia) and the Turgai River (Asia, Kazakhstan). Du ring the trapping period (4126 trap nights in total) 436 small mammals were captured. Twenty three voles belonging to Microtus arvalis super species were captured and identified in 10 of 16 localities. Presence of M. rossiaemeridionalis is originally demonstrated for 5 new localit ies, M. arvalis (obscurus?) was recorded in 6. The results obtained pr ovide the basis for accurate definition of southern borders of the ran ges for both Species thus contributing to the knowledge of their geogr aphic distribution and zones of sympatry.