Conspecific nest parasitism (CNP) is a widespread alternative reproductive tactic in birds. Several hypotheses have been put forward to explain the evolution and occurrence of CNP, but no generally applicable hypothesis exists. Recent experimental results from the common goldeneye (Bucephala clangula), a cavity-nesting duck, have revealed that parasitic females preferentially lay eggs in safe nest-sites, implying that nest predation risk is an important ecological determinant of CNP. The present study focuses on the mechanisms by which parasites identify safe nest-sites. Predation risk of a given nest-site was predictable between successive breeding seasons. At the end of the nesting season, females prospected active nest-sites more frequently than nest-sites that did not have a nest in the current season. Nest-sites that had been prospected more frequently by females in year t had a higher probability to be parasitized in year t + 1. The results suggest that the use of public information, derived through nest-site prospecting, enabled parasites to target safe nests. These findings provide a new and potentially generally applicable perspective to understand the evolution and occurrence of CNP.