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.
Spot-bellied eagle-owl
This is a very powerful and bold predatory owl, which is assuredly at the top of the avian food chain in its forested range. However, no extensive study of its dietary habits is known. Even in larger eagle-owls such as the Eurasian eagle-owl, although they can and do prey on a wide range of prey including impressively large prey, most of the diet consists of small mammals, often small rodents such as voles and rats. There is no reason to assume that the spot-bellied eagle-owl does not also take a very large quantity of relatively small prey such as rodents until complete dietary studies are known. However, almost all of the prey thus far reported for this species is very large and impressive, much of it being presumably as heavy or heavier than the eagle-owls themselves. Due to being most widely reported as being chased and eaten by spot-bellied eagle-owls has led some authors to list their primary prey as pheasants. Among these, junglefowl ("Gallus" sp.) and kalij pheasants ("Lophura leucomelanos"), both weighing from , are commonly eaten, as well as Indian peafowl ("Pavo cristatus"), which can weigh anything from . The spot-bellied eagle-owl pounces on gamebirds while they're asleep on their perches in trees or bamboo clumps, often killing them in seconds with their powerful talons. Cases, where they've followed peafowl to their roosts and then pulled them out at sundown, have been reported. It also consumes an array of mammals, from small rodents to large prey such as apparent adults of golden jackals ("Canis aureus"), hares ("Lepus" ssp.), large Indian civets ("Viverra zibetha"), Indian spotted chevrotains ("Moschiola indica"), and even young muntjacs ("Muntiacus" sp.). These larger mammals are likely as much as or even more. While most reported prey appear to be largely terrestrial, they are known to capture arboreal prey including Indian giant squirrel ("Ratufa indica") and juvenile purple-faced langur ("Trachypithecus vetulus"). Additionally, they are considered a potential threat to toque monkeys ("Macaca sinica"), and one apparently caught an Indian flying fox ("Pteropus giganteus") from its tree roost. Due to the capture of diurnal prey such as giant squirrel, partial daytime foraging habits have been inferred for the spot-bellied eagle owl. They will also opportunistically prey upon snakes, lizards (including large monitor lizards) and fish. Like several of the eagle-owls and fish owls but unlike most owls, the spot-bellied eagle-owl has been recorded as feeding on carrion. Thus far, they've been seen feeding on the carcases of goats ("Capra aegagrus hircus") and tigers ("Panthera tigris").