Food habits of the Great Horned Owl (Bubo virginianus) in a Patagonian steppe in Argentina

We studied seasonal variation in the diet of the Great Horned Owl (Bubo virginianus) through pellet analysis. Pellets were collected every month during 1995-96 from a steppe area in northwest Patagonia, Argentina. We identified 1216 prey items in 522 pellets. Rodents accounted for 98.5% of the diet while the remainder consisted of a variety of birds and insects, Rodents most frequently found in pellets were Eligmodontia morgani, Abrothrix longipilis, A. xanthorhinus, Oligoryzomys longicaudatus, Reithrodon auritus, and Ctenomys haigi. In terms of biomass. the most important species were R. auritus, A. longipilis, C. haigi, and E. morgani. Food-niche breadth was greatest in winter. Within the study area, the Great Horned Owl should he considered to be a rodent specialist all year round.