ARE RED-TAILED HAWKS AND GREAT HORNED OWLS DIURNAL NOCTURNAL DIETARY COUNTERPARTS

Red-tailed Hawks (Buteo jamaicensis) and Great Homed Owls (Bubo virgin ianus) are common in North America where they occupy a wide range of h abitats, often sympatrically. The two species are similar in size and have been portrayed as ecological counterparts, eating the same prey b y day and night. We tested the trophic similarity of the two species b y comparing published dietary data from across the United States. Both species ate primarily mammals and birds', and mean proportions of tho se two prey types did not differ significantly between diets of the tw o raptors. Red-tailed Hawks ate significantly more reptiles, and Great Horned Owls significantly more invertebrates. Dietary diversity was n ot significantly different at the level of prey taxonomic class, and d iet overlap between the two species averaged 91%. At the prey species level, dietary overlap averaged only 50%, and at that level Red-tailed Hawk dietary diversity was significantly greater than that of Great H orned Owls. Mean prey mass of Red-tailed Hawks was significantly great er than that of Great Horned Owls. Populations of the two species in t he western United States differed trophically more than did eastern po pulations. We conclude that, although the two species are generalist p redators, they take largely different prey species in the same localit ies resulting in distinctive trophic characteristics.