Dietary biology of the Eurasian eagle-owl
In the Iberian peninsula, the Eurasian eagle-owl is part of a complex guild of predators that have evolved to survive mostly on European rabbits. Among this guild, golden eagles ("Aquila chrysaetos") were recorded per one study to rely on rabbits for 40% of the diet, the eagle-owl for 49% of the diet, the Spanish imperial eagle ("Aquila adalberti") for 50% of the diet, the Bonelli's eagle ("Aquila fasciata") for 61% of the diet and the Iberian lynx ("Lynx pardinus") for 79% of the diet. Elsewhere, the Spanish imperial eagle and eagle-owl are considered to outflank the golden and even the Bonelli's eagle as the most specialized avian predator of rabbits in the Iberian region. Other predators, such as common buzzard ("Buteo buteo"), northern goshawk ("Accipiter gentilis") black kite ("Milvus migrans") Iberian wildcat ("Felis silvestris tartessia"), red fox, stone marten ("Martes foina") and introduced Egyptian mongoose also prey heavily on rabbits in Spain, but are more generalized and less reliant than the above predators. All these powerful predators do not generally compete directly for food but conflicts may ensue over the rights to territories and nesting sites amongst the birds. Being nocturnal in activity, however, the Eurasian eagle-owl does not tend to compete as directly as do the three eagle species and even these are discreetly segregated by habitat preferences, the goldens preferring open, steep cliffs, the Bonelli's favoring densely vegetated areas mixed with rocky spots and the imperial favoring relatively flat open woodlands. Among these eagles, the golden eagle tends to have the most similar habitat preferences to the Eurasian eagle-owl and across a broad band of overlapping distribution, the two are considered nearly ecological equivalents by day and night. However, good-sized female golden eagles are up to twice as heavy as an average eagle-owl, so seem to have a considerable advantage in size and power. Conversely, to support their large size and large territory needs, the golden eagle cannot survive on small and diverse prey nearly as successfully as the eagle-owl. Among the Iberian peninsula rabbit-eating guild, the species with wider ranges, the eagle-owl and the golden and Bonelli's eagles, have had some degree of success living off of alternate prey following the devastation of the rabbit population due to rabbit haemorrhagic disease. The two rabbit predators endemic to Iberia, the Iberian lynx and Spanish imperial eagle, have been devastated by the reduction and other causes and both are threatened species today.
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").