EN
Counts of birds wintering in river valleys and other objects in the Mazovian Lowland were conducted in the period 16-24 January, 2016 along 17 rivers of different size classes. Birds were also observed in other places of the concentration of waterbirds, such as towns and dam reservoirs. 95 observers participated in this action. In total, 1215 km of the river course were surveyed. The winter of 2015/2016 was rather frosty, and mean daily temperatures during bird counts varied between -5°C and -10°C. The water level in the Vistula River and its basin was within the mean and low zones. The surveyed water bodies were totally covered with ice. In January 2016, 104 wintering bird species were noted (tabs 1 and 2), with a total of nearly 80 thousand individuals. There were 39 species of waterbirds, with a total of 52 889 individuals. The most abundant species was the Mallard Anas platyrhynchos – 73.6%, rather abundant were also: Black-headed Gull Chroicocephalus ridibundus (4.8%), Goosander Mergus merganser (3.9%), Goldeneye Bucephala clangula (3.7%), Mute Swan Cygnus olor (3.5%), not identified large Gulls Larus spp. (3.2%), and Cormorant Phalacrocorax carbo (2.7%). Land species were represented by 65 species (table. 2.) with a total of 26 933 individuals. The most abundant were: Siskin Spinus spinus (12.2% of the assemblage, 27 ind./10 km) and Fieldfare Turdus pilaris (12% of the assemblage, 26.6 ind./10 km). The dominant species included also: Jackdaw Corvus monedula (8.1%), Yellowhammer Emberiza citrinella (7.9%) and Great Tit Parus major (6.9%). The mean density of birds was 221.7 ind./10 km, and it was similar to the mean from the previous five years (202.8 ind./10 km).