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Particularities of habitat and breeding conditions for birds in Yakutia, which occupies about one fifth of the area of Russia, are predominantly a sharply continental climate, the natural and diverse landscape, the development of the latitudinal and vertical zonation and the regime of summer light. Annual range of temperature has no parallel in the northern hemisphere – more than 100 °C, with the cold winters and hot summers. Due to extreme environmental conditions in winter, migratory birds (227 species) from the distant migrants compose 84.1% of the specific fauna in the region. Spatial and temporal contrasts of the breeding conditions cause a non-uniformly localized nature of bird distribution and high dynamics of their numbers, with many of them with being on the periphery of the species’ ranges. This leads to the formation of colonies in sites and many-species communities disposed to nesting in groups, with saturation unusual for high latitudes. Reduction of the qualitative and quantitative composition of the bird populations from main habitats, compared to more southern latitudes, is accompanied by an increase in the relative abundance of some of them, that leads to a narrowing circle of dominant species. Nest building is unpredictable year to year in seasonally unstable conditions. As a consequence, their periodic non-breeding is reported in the tundra (birds of prey, Siberian cranes, Ross’s gulls, etc.) and in the north- and forest-tundra subzones of the taiga – the abandonment of clutches and nestlings (Northern house martin). In the taiga zone of Yakutia, the potential total duration of possible terms for beginning of birds’ egg-laying composes more than 160 days (third week of February – third week of July). Bird nesting takes place in four stages, seasonally approximately to winter, summer, and two transitional periods (late winter–spring – April to mid May and the beginning of the spring- mid-April to early June), which are accompanied by phenology-climatic phenomenon playing the role of signals for the beginning of egg-laying. At the shifting of these stages, the corresponding shapes, structures, materials, locations, extents of nest cover, and types of food, are reported. Mass start of egg-laying (90.2% of species and 78.6% of nests) in the late spring and early summer is determined by migratory species. The nesting season of most birds is significantly reduced comparing with the southern latitudes and flows in the earlier phenologic conditions, and its initial phase and peak of the start of egg-laying intensity in species and separate pairs are shifted to the calendar later. In spite of the fact that birds with not many eggs per clutch are predominant (size classes mostly as 1–4 and 4–6 eggs), more than 80% of the species lay the same or somewhat larger number of eggs than in other parts of the area. With rare exceptions, the reproduction of birds is monocyclic, and a slight increase of egg numbers in clutches probably does not compensate inter-population prolific differences, because in the southern latitudes many species have several generations per season. |
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