Habitat use, feeding, diet composition, changes in body mass and interior indices, time budget, sex ratio and mortality of Mallards wintering in Belarus were investigated in 1980-1992. Counts and individual tagging allowed to reveal in wintering Mallards several functional groups, which use of wintering area was independent. The estimated number of Mallards in every wintering ground depended on food abundance in unfrozen feeding water bodies. The main food of 80% of Mallards wintering in Minsk city district was active silt from sewage plant. 80-90% of Mallards wintering in Lukomlskoe Lake (rural area) fed on Zebra Mussels Dreissena polymorpha. Body mass of Mallards studied increased from October till December and decreased from January till the middle of March (24% in females and 23% in males), and could have negative impact on reproductive success of sedentary Mallards. Time expenditure on flights and swimming decreased and foraging time increased from December till March. Mortality rate fluctuated between 1 and 6% in different winters.
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