Addition of eggs to nests of conspecifics is a common avian alternative breeding strategy, called conspecific brood parasitism. The consequences of this breeding strategy on recipient breeding success have seldom been quantified, while taking into account environmental factors and host female characteristics. We study the occurrence of nest parasitism and, using an information theoretic approach, the most important factors responsible for nest desertion in female Barrow's goldeneyes (Bucephala islandica). Nest parasitism is common in the study populationpopulation, and 58% of the nests contained non-natal eggs, representing 20% of all eggs. A prime factor explaining nest desertion was the number of non-natal eggs. There were also significant effects of year and own clutch size. By contrast, ambient temperature and female laying date did not influence nest desertion. These results provide one of the first demonstrations that non-natal eggs can have substantial negative effects also in precocial species.