Owls are efficient predators and are widely distributed around the globe. Remains of undigested prey is regurgitated by these birds in the form of pellets, and these are a valuable source of information about prey communities and the diet of owls. In this study, the composition of mammals present in the diet of owls that inhabit different caves was evaluated through the analysis of their pellets. We found 373 pellets from seven caves, and small mammals composed at least 80% of the diet of these birds in all caves. The mammal composition found in the pellets showed a richness of 26 distinct taxa including 12 rodents, three marsupials and 11 bats. In this work, we highlight the richness of small mammals in a poorly known Caatinga area. We also highlight the importance of morphology and taxonomy in supporting this kind of research, which relies upon vertebrate parts as its source of information for identification. Finally, we reiterate the efficiency of the study of owl pellets as a rapid approach for assessing local mammal richness and as a complementary method in studies of diversity and conservation.