The Mexican Spotted Owl (Strix occidentalis lucida), one of the three subspecies of the Spotted Owl recognized within the United States, is designated as threatened under the Endangered Species Act. Arizona’s Walnut Canyon National Monument has been designated as critical habitat for it. This continuing study focuses on composition of the species’ diet through the identification of prey items found in its regurgitated pellets. Similar research has taken place in surrounding areas (Ganey 1992, Block et al. 2005; J. Ganey pers. comm., 2020), but this is the first such study within the national monument. In my pilot study, in 2018, my collaborators and I gathered 48 pellets (comprising 1600+ individual bones), then in 2020 an additional 70 pellets (comprising 3100+ individual bones). In total they included the bones of rodents, small passerine birds, shrews, bats, and a single owl. Pellets gathered in 2020 were dissected and analyzed in early 2021. At that time five Spotted Owl territories were known in the canyon.