Altitudinal belt differentiation of bird population in the central part of the Verkhoyansk Range (Eastern Siberia, Russia)

The knowledge of ecological and geographical patterns of mountain bird fauna and population formation is considered to be one of the most vital issues of modern ornithology. The obtained data can be used in the monitoring and development of biodiversity conservation measures. In our study, we analyzed ecological patterns of the altitudinal belt differentiation of bird population in the central part of the Verkhoyansk Range. We collected data during expeditions carried out in summer 2014 in the Nyamni river basin (6430'N, 13232'E) and in 2015 - on the Arkachan plateau (6543N, 13010'E). We conducted studies in the regions with three distinct altitudinal belts: forest (1000 m asl), subalpine (1000-1200 m asl) and alpine (1200-1700 m asl). The survey was conducted by the method of route accounting in transects of unlimited width. We analyzed the fauna of nesting birds in terms of species belonging to the faunal complexes and the geographical-genetic groups. We determined the avifauna similarity of the compared areas and altitudinal belts by the S0rensen and Jaccard faunal commonness coefficient. We used the population similarity coefficient to identify differences in the bird population of several areas. Our studies established that 67 species of birds nest in the surveyed areas of the Verkhoyansk Range including 62 species in the Nyamni river basin and 42 species on the Arkachan plateau. Species richness reduces with height. The avifauna basis of the three belts of both regions is formed by passerine species (44-71%). In the Nyamni river basin, groups of waders (8-25%) and birds of prey (8-13%) are also significant in each belt. The ratio of different taxonomic groups' representatives in each altitudinal belt is more unstable on the Arkachan plateau, and more similar in the Nyamni river basin. We proved that due to the large number of common species in neighboring belts, changes in bird species composition with height take place gradually. The maximum relative similarity in both areas is typical of the avifauna of forest and subalpine belts (42 (26)-67 (50)%), the minimum - the avifauna of forest and alpine belts (9 (5)-25 (14)%). The similarity of the aviafauna of two areas at the level of the forest belt is 71 (55)%, the subalpine belt - 44 (28)% and the alpine belt - 52 (35)%. We noted that the proportion of species of different faunal complexes is variable within the entire vertical profile. The most significant part is taken by species of Siberian (31-61%) and widespread (25-43%) faunal complexes. In addition, we revealed that the most significant part in aviafauna formation of two lower altitudinal belts belongs to species of widespread (31-41%), boreal (17-37%) and boreal-hypoarctic (17-25%) geographical-genetic groups. In the alpine belt, a group of arctic-alpine species (25-57%) also plays an important role. Thus, the nesting bird population density decreases with height. The bird population density in the forest belt ranges from 409 to 544 ind./km2, in the subalpine belt - from 112 to 296 ind./km2 and in the alpine belt - from 56 to 126 ind./km2. The similarity of bird populations in two areas at the level of the forest belt is 50%, the subalpine belt -20% and the alpine belt - 28%.

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