Long-term changes in duck inter-specific nest parasitism in South Bohemia, Czech Republic

Inter-specific parasitism in duck species in Central Europe may be an accidental consequence of conspecific breeding parasitism. Analysis of 1,237 nest records for five duck species in South Bohemia from 1999–2008 found that parasitism, where a bird lays its eggs in the nest of another species, had occurred in 6.6% of nests. Three Red-crested Pochard Netta rufina clutches were all parasitised and Red-crested Pochard most often laid parasitic eggs in the nests of other species. Gadwall Anas strepera was the second most parasitised species, with non-Gadwall eggs found in 16.4% of 152 Gadwall nests checked. Mallard nests were the least likely to be parasitised and Mallard Anas platyrhynchos also laid relatively few parasitic eggs. There was a significant correlation between the probability of each species being parasitised and of its being a parasite. The results were compared with those in an earlier publication on the frequency of inter-specific clutch and nest parasitism in South Bohemia. Inter-specific breeding parasitism was more frequent in 1975–1980, in the years of increasing population size for all five species, when 13.9% (n = 284 nests) of clutches were found to have been parasitised.