Distribution characteristics of geographic races of some passerine birds in the Eastern Caucasus

The study of distribution characteristics of subspecies forms is of great importance to understand processes of geographical species formation. It essentially broadens our knowledge of population structure of particular species, and allows more accurate assessment of avifauna differences between relatively small physical-geographical regions, such as the Eastern Caucasus. By the Eastern Caucasus, we mean the northern and southern macroslopes of the Greater Caucasus with the adjacent plains within the borders of Northern Azerbaijan, Daghestan, Chechnya and Ingushetia. The objective of this research was to clarify in the Eastern Caucasus the distribution limits of geographical forms of some bird species of the order Passeriformes, which had been believed to be represented in the area by two or more subspecies. The results of the study indicate that for such species as Alauda arvensis, Sturnus vulgaris, Acrocephalus scirpaceus, Saxicola rubicola, Saxicola maurus, Passer domesticus, Passer montanus, and Linaria cannabina, the distribution of only one subspecies should be recognized as reliable in the Eastern Caucasus, contrary to the previous ideas. At the same time, it is the area where a number of Transcaucasian subspecies such as Galerida cristata caucasica, Calandrella rufescens pseudobaetica, Anthus campestris boehmii, Sylvia communis icterops, Sylvia curruca caucasica, and Carduelis carduelis brevirostris penetrate into the northern macroslope of the Greater Caucasus, thus reflecting its zoogeographical isolation in respect to other regions of the Northern Caucasus.