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.