Number Dynamics of Shorebirds and Waterfowl in “Cold” Wintering Grounds at Headwaters and Upper Reaches of the Angara River during the Warming Peak

Based on long-term research (2012–2017), we have analyzed the population dynamics of waterfowl in their cold wintering grounds at the headwaters and upper reaches of the Angara River. It is shown that this period coincides with the maximum level of climate warming, a multi-century trend lasting approximately 2,000 years. The warming peak was observed in 2015. The number of waterfowl during this period increased until 2013 (25,503 birds), and then began to decline (11,054 birds in 2017). It has been proven that a sharp decline in the number of wintering birds is associated with a noticeable increase in the duration of the warm autumn period, favorable for the departure of migrating birds. The last migrating flocks of Vegae Larus vegae and Mongolian Larus mongolicus Gulls with individual birds and small groups of Heuglin’s Gull Larus heuglini were observed on December 3, 2013 and December 13, 2024. The departure of the last flocks of Goldeneyes Bucephala clangula was recorded at the same time. Late migratory flocks reached numbers from 70–80 to 120–150 gulls and 3,000–5,000 Goldeneyes. Having not yet accumulated the necessary level of plastic substances (fat) used as energy resources during the period of active migration late-migrating birds are forced to stay for the “cold” winter. By the time they accumulate the necessary level, but departure becomes impossible due to the extreme severity of winter conditions. It has been proven that the number of birds staying for the “cold” winter is primarily determined by temperature conditions and the duration of the autumn period. When autumn sets in early and is cold, migration usually ends earlier and the number of birds in the “cold” wintering grounds increases.