On the basis of long-term works (1984–1992) in headwater stuffs of Angara river on the data selective elimination of goldeneye Bucephala clangula females on «cold» wintering grounds of this region are resulted. The expressed intersexual dimorphism in dimensions (females in 1,3–1,5 times there are less than males) gives priority to drakes at feeding on fields with a rapid current. They lose less energy and is better conserve mass of a body during a wintering ground. Females lose mass of a body faster and move along the edges of an ice-hole with the worst foraging conditions. In cold winters and deficiency of foodstuffs organism expenses on heat production increase and to 69,0 % of birds perishes from an attrition. Below the weir of Irkutsk Hydroelectric Power Station of a condition of a wintering ground are more congenial that leads to concentration here females and young birds and their best survival rate even in severe winters. The result of selective elimination of females is sharp growth of a male proportion in the vernal season (before the beginning of a season of reproduction).