Intraspecific and interspecific brood parasitism occur frequently in waterfowl. We examine the consequences of these behaviors to the population dynamics of Barrow's and Common Goldeneyes during a 10 year study period in central British Columbia. The frequency of parasitism was significantly related to population density and to the availability of nest sites. High levels of parasitism, in turn, resulted in reduced reproductive success of females. Using a simulation model based on field data, we demonstrate that high frequencies of intraspecific parasitism can lead to the extirpation of local populations. Brood parasitism between species leads to the additional complication that parasite offspring may become sexually imprinted on the host species, thereby facilitating cross-mating and interspecific hybridization. We test this hypothesis using (1) a comparative analysis of the Anseriformes and (2) field studies and molecular genetic analyses of interspecific hybridization in goldeneyes. Our results demonstrate that social interactions such as brood parasitism may play an important role in determining the long-term viability of local populations.