SummaryIntraspecific nest parasitism was recorded in 31% of clutches containing±5 eggs laid by Maned DucksChenonetta jubatain nest boxes near Canberra. This is within the range for other cavity-nesting waterfowl. Frequency of parasitism was higher in 1987 (62% of 13 incubated clutches) than in 1988 (27% of 22 incubated clutches). Less rain fell during the laying period in 1987 (209 mm) than during the same period in 1988 (309 mm). Rain increases the growth of pasture grazed by Maned Ducks. The higher incidence of parasitism in the drier year suggests that individual Maned Ducks used nest parasitism as a salvage strategy, to enhance their chance of reproductive success when food was relatively scarce. Natural and experimental parasitism did not increase nest desertion, nor did they reduce clutch size of hosts, fat levels of incubating females or egg hatchability. Larger broods survived as well as smaller ones. Thus, nest parasitism in Maned Ducks may increase the reproductive success of the parasite, without reducing the reproductive success of the host. The sample sizes in this study were small and more data are required to confirm these tentative conclusions.