These birds wait on a high perch at night and swoop down on prey. They mainly eat small organisms with a strong focus on small mammals in their diet. Swengel and Swengel (1992) reviewed ten studies that found northern saw-whet owls eating almost exclusively mammals (88% to 100%), with most of the mammals being rodents (85% to 99+%). Specifically in their Wisconsin study, the Swengels counted saw-whet owls as most often eating deer mice, ("Peromyscus"; ~68% of captured prey), voles ("Microtis pennsylvunicus" and "M. ochroguster"; ~16%), and shrews (~9%; "Blurinu brevicuudu" and "Sorex cinereus"). A similar study by Holt and Leroux (1996) in Montana found saw-whet owls eating more voles (60%) than other mammal species. Engel "et al". (2015) also found in the saw-whet owl a strong preference for small mammals (89%), with 55% of prey being two species of voles.