Dietary biology of the Eurasian eagle-owl
Generally speaking, there appears to be rather strictly adhered size hierarchy among birds of prey and the very largest raptorial prey attacked by Eurasian eagle-owl tend to roughly equal to their own size. Larger raptors, such as eagles and vultures, seem to be largely invulnerable to eagle-owls. However, in Scandinavia, there are two cases of eagle-owls preying on “fairly large” nestlings of white-tailed eagles ("Haliaeetus albicilla"). Given the size, average adult weight of , and formidable character of this eagle, it is possible that the young of other raptors larger than themselves may too be attacked. Eastern imperial eagles ("Aquila heliaca"), which are nearly as large as the white-tailed eagle at an average weight of , have been killed by eagle-owls in Kazakhstan. Remarkable, considering the greater threat that the eagle normally poses to the eagle-owl than vica versa, it appeared a golden eagle was amongst the prey remains found around a nest in the French Pyrenees. Cases in Spain where large, formidable birds of prey, the Egyptian vulture ("Neophron percnopterus") and Bonelli's eagle, that are roughly equal in size to the eagle-owls, both weighing just over , have been predated, these seem to be taken from the nest or shortly after independence and rare occurrences. However, in Turkey, the eagle-owl is apparently a regular and serious predator of Bonelli's eagles. The Eurasian eagle-owl predates the largest members of the most species-rich diurnal raptor genera: the northern goshawks from the "Accipiter" genus, the upland buzzards from the "Buteo" genus and the gyrfalcons ("F. rusticolus") of the "Falco" genus. Additional large raptors, i.e. those that can average or more in body mass, taken as prey include osprey ("Pandion haliaetus"), the red kites ("Milvus milvus"), short-toed eagles ("Circaetus gallicus"), the greater spotted eagle ("Clanga clanga"), the lesser spotted eagle ("Clanga pomarina"), and the rough-legged buzzards ("Buteo lagopus") and saker falcons ("Falco cherrug"), in both of which females average more than . The taking of rough-legged buzzards and snowy owls must be confined to full-grown victims, since they nest further north than Eurasian eagle-owls. Eurasian eagle-owls also hunt the smallest raptors available, including those such as lesser kestrels ("Falco naumanni") and Japanese sparrowhawks ("Accipiter gularis") that weigh less than . Some of these are cases of eagle-owls killing nestlings or fledglings but they can easily overtake adult buzzards, goshawks and falcons of any size.
Verreaux's eagle-owl
Despite the alternate common name of giant eagle-owl, the Verreaux's eagle-owl is not the largest owl or eagle-owl in the world. It is, however, a very large and powerful owl species. This species is both the largest owl found in Africa and the world's largest owl to occur in the tropics. Among all the world's owls, it is fourth heaviest living owl, after Blakiston's fish owl ("Bubo blakistoni"), the Eurasian eagle-owl ("Bubo bubo") and the tawny fish owl ("Bubo flavipes"), and is also the fourth longest living owl (measured from the bill to the tip of the tail), after the great gray ("Strix nebulosa"), Blakiston's fish and Eurasian eagle-owls. Based on body mass and wing chord length, Verreaux's eagle-owl is about the same size as "medium-sized" races of Eurasian eagle-owl, such as those from Central Asian steppe ("B. b. turcomanus") and the Himalayas ("B. b. hemachalana"), slightly smaller than most northern Eurasian races, considerably smaller than Siberian and Russian eagle-owls, and somewhat larger than the smallest Eurasian eagle-owl subspecies, such as those from the Iberian Peninsula ("B. b. hispanus") and the Middle East ("B. b. omissus" or "nikolskii").