Seasonal Variation in the Diet of Great Horned Owls (Bubo virginianus) on Shortgrass Prairie

Abstract

-We collected and analyzed pellets from known roosts of great horned owls (Bubo virginianus) on shortgrass prairie in N-central Colorado between 1992 and 1994 to examine seasonal trends in owl diets. We also compared the species composition of small rodents in owl diets to the relative abundances of rodents on the study area. In all seasons, lagomorphs (desert cottontails Sylvilagus audubonii, black-tailed jackrabbits Lepus californicus, white-tailed jackrabbits Lepus townsendii) comprised most of the diet biomass. Northern pocket gophers (Thomomys talpoides) were also preyed upon in all seasons, with the highest percentage consumed in spring. Most of the individual prey items taken were rodents, primarily deer mice (Peromyscus maniculatus). Comparisons of diet composition with measures of rodent abundance suggested that owls foraged over a relatively restricted part of our study area, especially in winter. Most prey apparently were taken from roadsides, buildings and an adjacent four-wing saltbush (Atriplex canescens) floodplain, where rodent densities remained relatively higher in all seasons than in the surrounding vegetation. We speculate that the preferential use of these foraging habitats may reflect the availability of suitable hunting perches on the site.