Intraspecific and interspecific nest parasitism in ducks in the south of Western Siberia (Northern Kulunda)

Intraspecific and interspecific nest parasitism is wide spread in ducks. However, these phenomena were studied severally. The present study aims to quantify the frequency of both kinds of parasitic shedding of eggs and to find out how it depends on the relative abundance of each species in the breeding duck community. We examined these phenomena among waterfowl nesting on Lake Krotovo, Western Siberia. The study was carried out from 1970 until 2016. Complete searches for duck nests were conducted at 7–10 days intervals from early May to late July. A total of 6654 duck nests were found and monitored. On each nest visit all eggs were censused and labelled with indelible felt pens. Eggs were identified according to their color, size, shape, or stage of development. The parasitism degree was defined as the ration between the number of nests containing “foreign” eggs and the total number of studied nests of a particular species. To assess the results, we used Student's t-test, Mann-Witney U test. To establish the contingency of the parasitism level and the number of a species, Pirson correlation and Spearmen correlation analysis were applied. It was shown that all the species nested on Lake Krotovo took part in both interspecific and intraspecific nest parasitism. Relative abundance of each species varied from year to year. In the most abundant duck species (Mallard, Pochard, Tufted Duck), the proportion of intraspecific parasitic eggs (e.g. laid in the nests of the same species) was significantly greater than that of interspecific eggs (e.g. laid in the nests of another species). In the least abundant duck species, conversely, the proportion of interspecific parasitic eggs was greater. The common level of parasitic egg-laying in Pochard did not significantly depend on its number on the Lake. Pochard and Gadwall more often parasitized on the clutches of another species, when the proportion of its nests on the Lake decreased, and more often parasitized intraspecifically, when the relative representation of this species in the breeding duck community increased (r = 0.61; p