AN ANALYSIS OF THE BIRD FAUNA AND POPULATION IN THE SOUTHERN SPURS OF KOLYMA HIGHLAND
In our study, we analyzed the ecological patterns of altitudinal differentiation of the bird fauna and population in the southern spurs of Kolyma Highland. The studies was conducted in the regions (n = 11) with three distinct altitudinal belts: forest (1000 m asl), subalpine (1000–1700 m asl), and alpine (2600 m asl). The survey was conducted by using route accounting in transects of unlimited width. The fauna of breeding birds was analyzed in terms of species attributed to certain faunal complexes, as well as geographic and genetic groups. The similarity of the avifaunas of the areas and altitudinal belts compared was determined using the Sørensen and Jaccard similarity indexes. A population similarity coefficient was applied to identify the differences in the bird populations of several areas. The similarity of the taxonomic structure and species composition of nesting birds in the region which supports 74 species was found high. A number of species (n = 16) were recorded for the first time as nesting in the southern spurs of Kolyma Highland at a distance of 20–800 km off their northern range limits. The taxonomic structure of nesting birds corresponds to the zonal and landscape features of Northeast Asia, with species of Passeriformes, Charadriiformes and Anseriformes dominating and taking up to 83% of the overall diversity. Species of the Siberian faunal complex (33–49%) prevail in the avifauna. From the viewpoint of zoogeography, the bird fauna of the southern spurs of Kolyma Highland shows certain peculiar traits due to species (n = 8) ecologically linked to mountainous landscapes. The avifauna of the southern spurs of Kolyma Highland must have been developed following the general zonal-landscape and altitudinal zonal principles. The species diversity of birds drops from foothills to mountain tops. Changes in species composition with elevation occur gradually. In the forest belt, 69 species (92%) are nesting, vs. 33 species (45%) and 15 species (20%) in the subalpine and alpine belts, respectively. Over a wide range of altitudes that cover at least two high-montane belts there are 45% species. In the southern spurs of Kolyma Highland, the population density of birds and their abundance progressively drop with altitude in most species. The population density decreases mainly in the areas where the subalpine belt is replaced by the alpine one. The bird population density of the forest belt amounts to 176–674 ind./km<sup>2</sup>, vs. 76–230 ind./km<sup>2</sup> and 20–72 ind./km<sup>2</sup> in the subalpine and alpine belts, respectively.