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While the impacts of predators on prey demography are well studied, relatively few studies have explored how predators affect the population genetics of prey. I investigated the effects of predation pressure on genetic diversity and genetic similarity in song sparrows (Melospiza melodia) and the demographic mechanisms (births, deaths and dispersal) that may drive this relationship. I compared genetic diversity and genetic similarity (measured at 13 neutral microsatellite loci) between landscapes (island and mainland), and between populations within each landscape. In every comparison, sparrows inhabiting the landscape or population with higher nest predation were more related to one another, and in one comparison, had lower genetic diversity. High nest predation also was associated with reduced birth and population growth rates, and increased variance in reproductive success. Thus, the effects predators have on prey demography may negatively impact the genetic diversity of prey populations, beyond their effects on prey population size.