Formation of a “cold” winter of shorebirds and waterfowl in the source and upper current of the river Angara (South Baikal) and its causes

Abstract

On the basis of many years of research (1972-2019), the peculiarities of the formation of “cold” wintering of near-water and waterfowl in the source and upper reaches of the Angara river are considered. Despite the fact that it has been for a very long time studied, this issue has not yet received proper coverage in the scientific literature. Until now, there are different opinions about the reasons for its formation - sometimes very controversial, which requires a more complete analysis of the available materials. We found out that the formation of wintering is associated with delays in the departure of birds that have not accumulated a sufficient amount of plastic substances necessary for the continuation of migration. Late freezing source and upper course of the Angara river (mid-January - early February) allow birds to stay for a long time. Here, due to the huge mass of water heated in summer, which increases the temperature of the surface air layer in the late autumn and early winter periods, a thermal is refugium formed. However, by the time the birds are able to continue their migration, it becomes impossible. Permanent snow cover and very low air temperatures are in the surrounding areas established, and all lake systems freeze. This thermal refugium, into which birds, delayed with flight, gradually move, becomes an ecological trap, and the “cold” wintering itself is forced.

Waterfowl and Shorebirds: Formation and evolution of “cold” wintering grounds in Inner Asia (Baikal Siberia)

“…In the second half of the 20th century (the 70s), we began intensive research on "cold" wintering in the source and upper reaches of the Angara River. For the first time, special methodological approaches to accounting for wintering waterfowl were developed and their numbers were fairly accurately determined, as well as their changes over a long period [2,9,[14][15][16][17]. It was at this time that the general warming of the climate began to affect wintering waterfowl and some increase in their numbers was noted.…”

“…By this time, all lakes and small streams and rivers had long been frozen and stops of coastal birds for rest and feeding were possible only on the Angara River and Lake Baikal. In such cases, the sudden onset of cold weather forced the birds to stay here for the "cold" winter, and after the complete freezing of Lake Baikal to concentrate at the source of the Angara River [9]. It was these conditions, acting as an ecological trap for birds, that forced them to stay on vacation in its upper reaches, located within the forest-steppe, and then stay here for forced wintering.…”

“…The number of birds in such "cold" wintering grounds can reach -55.0-60.0 thousand birds (the source and upper course of the Angara River) [2], however, the exact reasons for their formation are still unknown. Various authors have made several assumptions about the main directions of their formation and evolution, some of which are undoubtedly correct, but there is still no final decision on this issue [3][4][5][6][7][8][9].…”

“…The solution of these issues is of great importance for the proper organization of their protection and the development of measures to maintain the number of birds in extreme conditions of some very harsh winter seasons. During such periods, the surface air temperature drops below -40.0° C, the area of sagebrush is sharply reduced to the minimum possible size, and bird mortality can reach 69.0% [2,[8][9]. The presented work deals with special issues related to the formation, maintenance of bird numbers and the evolution of "cold" wintering grounds in Inner Asia, as well as the organization of their protection as a unique natural phenomenon.…”