Nesting of the white-headed duck (<i>Oxyura leucocephala</i>) in Barabinskaya lowland and Kuludinskaya steppe
<i>There were investigated 200 wetlands. As a result of registration there have been discovered 1041 specimens of a white-headed duck, 14 nests of the white-headed duck, 33 broods, and taken 85 samples of plankton and benthos during three years. In order to study the nesting, there were chosen 5 model wetlands, where the sets of hidden video cameras recording the whole brooding period were mounted. The nests are located on reed bogs on the edge of the primary reach or by small inner reaches. They are built from dry parts of reed with a small amount of fuzz. Different investigators found fresh layings from the 27th of May to the 10th of July in different years. According to our data, the average number of the laying is 7,7 eggs (n=10). The average sizes of eggs are 69,63±0,43 х 50,88±0,45 mm (n=71). The average mass of one egg is 95,44+1g (n=40). The weight of females varies from 500 to 890 g., i.e., the total weight of the laying is 98-170% of the female weight, and the weight of separate eggs can make up to 15-20% of the female weight. We noted nesting on the lakes with the biomass of plankton not less than 66 g/m3 and biomass of benthos not less than 10 g/m2. The correlation ratio (r) between the number of the white-headed duck and biomass of benthos is 0,9224. Apparently, the white-headed duck is very conservative in choice of wetlands, especially on nesting, which is also indicated in papers of G.S. Dzhamirzoev with co-authors and other authors. During the reproduction period the white-headed duck needs a large concentration of food on the wetland to lay its large eggs. The forage biomass depends in its turn on the water level- places of the white-headed duck habitation. Thus, we consider the forage biomass (which depends on the water level) one of the main factors influencing the choice of a wetland by a bird for nesting. What are the reasons for the anomalously big sizes of the white-headed duck eggs? Probably, the way of its evolution developed not by the way of "quantity", but by the way of "quality". Due to a large mass of the egg, the nestlings appear stronger and therefore the white-headed duck has lower death rate of nestlings than other ducks do. For example, according to unpublished data of V.A. Shilo and S.N. Klimova, the hatched out nestlings of the white-headed duck can loose up to 27% of their mass without a lethal outcome, which is not observed at other species of ducks. Most likely that the white-headed duck developed by the way of increasing the survival rate of nestlings, which explains a large mass of its eggs. Hatching of nestlings in nature occurs on the 22-25th day. The average size of a brood is 5,51 birds. The "coupled" broods are observed by the white-headed duck, i.e. when one white-headed duck leads two and more broods. Apparently, females often leave a brood without care by early August. Out of all broods fixed in August, young birds have not been accompanied by females in 84% of cases. Young white-headed ducks rise on their wings from late August to middle September. </i>Key words: <i>white-headed duck; Oxyura leucocephala; nesting; Western Siberia.</i>