Comparative Food Habits of the Eagle Owl Bubo bubo and the Great Horned Owl Bubo virginianus in Six Palearctic and Nearctic Biomes

Abstract

Food habits and trophic convergence between Palearctic Eagle Owl and Nearctic Great Horned Owl were studied on the basis of the taxonomic composition of their diet, trophic diversity and mean weight of prey. Within each faunal region six biomes were distinguished: Mediterranean shrubland, temperate deciduous forest, boreal conifer forest, grassland, temperate desert, and mountain. Three prey assemblages dominated the diet of the two owls but maximum frequencies were not always attained in similar Palearctic and Nearctic biomes. Thus, lagomorphs dominated in the Mediterranean shrubland (Eagle Owl) and temperate deciduous forest (Great Horned Owl), respectively; voles (Cricetidae) dominated the diet of both owls in the boreal conifer forest; desert rodents (gerbils, jerboas and kangaroo rats) and invertebrates dominated their diet in deserts. The diet of the two owl species reached maximum trophic diversity in temperate deciduous forest and deserts and minimum mean weight of prey in the deserts. Great Horned Owls tended to have a more diverse diet than Eagle Owls. Limited trophic convergence between the two species of owl could be due to differences between similar Palearctic and Nearctic biomes in the composition of prey assemblages and abundance of the preferred prey (lagomorphs), and to intraand interspecific differences in the body weight of the owls.