Most socially monogamous bird species engage in extra-pair mating, and consequently males may adopt various behavioral strategies to guard paternity. However, the relationship between mate guarding and extra-pair paternity is unclear: low levels of extra-pair paternity can be associated either with no mate guarding or with intense mate guarding. We investigate paternity guards in the purple-crowned fairy-wren (Malurus coronatus), a duetting species where extra-pair paternity is rare. This species is unusual in a genus known for extremely high levels of extra-pair mating. We examine the behavioral interactions between the sexes underlying these low rates of extra-pair paternity and show that male purple-crowned fairy-wrens do not use frequent copulation or courtship feeding to assure paternity or guard females acoustically by duetting. Males maintain close proximity to females both when they are fertile and when they are not breeding and do not invest in courtship displays to extra-pair females. Consistent with predictions of theoretical models, low extra-pair paternity in this species may be related to female fidelity rather than male paternity assurance strategies, but short-term removal of males would be necessary to test this experimentally.