Spatial and typological structure of autumn-summer and autumn populations of birds of the northern macroslope of the Kyrgyz range (Tian Shan)

In the autumn-summer and autumn periods, post-nesting migrations significantly change the appearance of spring-summer ornithocomplexes. In this connection, it is of undoubted interest to identify a set of environmental factors that determine the heterogeneity of the ornithocomplexes' structure in the indicated seasons in comparison with the preceding ones. The aim of this research was to describe changes in the structure of the bird population of the northern macroslope of the Kyrgyz ridge during these periods and compare it with the structural changes in the Altai mountains. The results of bird counts conducted from June 16, 1991 to June 15, 1992 on the northern macroslope of the Kyrgyz ridge were analyzed. The seasonal aspects of the bird population were determined by the obtained abundance indicators using the method of ordered classification separately for each level of heights (high mountains, middle mountains, foothills). 22 habitats were surveyed in both periods. The studies were carried out on the routes with no restriction on the width of the transect, with recalculation of the data for the average group detection distances. Within every habitat, 5 km of the route was covered with a two-week repetition. In total, 550 km were covered for both seasons. The research showed that strustural classification of the bird population of the Kyrgyz range in the autumn-summer and autumn seasons illustrates the existence of three systems of bird population: undeveloped, built-up land and water habitats. Water communities of birds form a single ornithocomplex type, regardless of the altitude. In autumn and summer, on the Kyrgyz ridge, the number of allocated types is reduced by half compared to the previous seasons (spring and spring-summer) due to post-breeding dispersal of birds (See Fig. 1 and 2). In autumn, the number of types on the Kyrgyz ridge increases to 10. The importance of afforestation, productivity and altitudinal zonation in both periods is almost the same. The influence of the composition of forest-forming species, water availability, bushiness and food capacity is several times higher in the Altai mountains than on the Kyrgyz ridge (See Table). On the contrary, water content and building degrees, cattle grazing and the presence of rocks and talus have a greater impact on the Kyrgyz ridge. The number of the registered bird species in the Altai is much larger than on the Kyrgyz ridge, and vice versa for background species. There аге 26 leading species on the Kyrgyz ridge and 35 in the Altai mountains. The common leaders for both regions were 10. More mountain and synanthropic species are leading on the Kirghiz ridge. In the Altai, there are more forest and wetland species among the leaders. On the Kyrgyz ridge, these are predominantly passerines, and in the Altai, in addition, plate-tailed birds and waders. The total abundance and biomass of birds is greater on the Kyrgyz ridge, the maximum indicators are characteristic of foothill settlements. In the Altai, there are more invertebrates and vertebrates in the birds' diet, as well as vegetative parts of plants, whereas there are more seeds and juicy fruits on the Kyrgyz ridge. In the autumn-summer period on the Kyrgyz ridge and in the Altai, Tibetan birds prevail in the highland belt. Mediterranean birds are rare in the Altai, whereas on the Kyrgyz ridge they are encountered in significant numbers in all belts. Species of the European fauna type in the Altai prevail in all belts, and on the Kyrgyz ridge, mainly, in the foothills and highlands. Birds of the Mongolian fauna type prefer highlands and foothills of the Kyrgyz ridge and foothills and middle mountains of the Altai mountains. Chinese species were recorded as predominant in the high mountains of the Kyrgyz ridge and in all high-altitude belts of the Altai mountains. The Siberian fauna type is abundantly noted in the high mountains of the Kyrgyz ridge and in the middle mountains and highlands of the Altai. Arctic birds in the Altai were not encountered in the considered seasons, and on the Kyrgyz ridge they were detected in small numbers in the high mountains. The indicators of the total abundance and biomass in autumn are less than in the autumn-summer period. As a result of migration, population density and species richness increased in foothill habitats, whereas on the rest of the territory they decreased. In the diet of birds, the number of seeds and juicy fruits on an energy equivalent basis increases in autumn, and the number of invertebrates decreases. The proportion of birds finding food on the ground was almost unchanged compared with the previous period; that from air and shrubs decreased, and that from other tiers increased. Tibetan and Mongolian species still occur in significant numbers in the highlands in autumn. They were detected also in the foothills. In all belts, in autumn, European and Siberian birds joined the leaders of the previous season due to the autumn migration. There were more Chinese forms in the foothills, in contrast to the autumn-summer period. The strength of the connection with environmental factors is almost identical with the summer-autumn period. The heterogeneity of the ornithocomplexes is significantly determined by water content, productivity and food capacity of habitats and somewhat less by afforestation and bushiness. The absolute height of the terrain affects even less, and the building degree, on the contrary, affects greater. In autumn, the influence of all environmental factors together does not change compared to the autumn-summer period; the indicators of natural-anthropogenic modes are higher. Thus, the characteristic difference between habitats of arid zones and humid ones is a decrease in the number of types in the second half of summer (summer-autumn period). The total abundance and background richness is greater on the Kyrgyz ridge. Passerines are leaders for the Kyrgyz ridge; waders and plate like birds are leaders for the Altai. In the Altai, forest and water-swamp birds are more prevalent, whereas mountain and synanthropic species predominate in the Kyrgyz ridge. The species composition in both mountain regions are the same, but in different seasons and high-altitude zones the ratio of their abundance and species number varies. In autumn, the spatial heterogeneity of the bird population of the Kyrgyz ridge differs from the previous season: the number of identified population types increases almost twofold. The paper contains 2 Figures, 1 Table and 22 References.

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