Birds can recognize their predators and adopt distinct strategies to avoid predation. We conducted a series of field experiments in Southeastern Brazil to investigate the ability of birds to discriminate between closely related predators. We achieved this through the presentation of a series of models and/or vocalizations of closely related owl species that represent various levels of danger and familiarity to the local bird community, and measured the composition and intensity of the mobbing that ensued. We found that the birds did not differentiate between owls of the same genus (within both Asio and Glaucidium), whether they were familiar (occur in the study area) or unfamiliar (occur outside of the study area). However, when presented with similar, although less closely related, diurnal owl species which represent different threat levels, the birds mobbed the dangerous predator less intensely, but in larger groups, than the non-dangerous predator. These results suggest that birds can access general information about familiar predators and extrapolate when faced with an unfamiliar predator. Additionally, the birds demonstrated that they can recognize distinct predators with regard to the threat they pose, and choose different strategies to deal with each degree of risk. These studies highlight that birds exhibit a complex system of predator recognition that allows careful discrimination between threat levels in familiar situations, while allowing for generalization in unfamiliar situations.