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.
White-tailed eagle
Although other birds of prey are seldom caught, given that they are wary, fast and can defend themselves well, the white-tailed eagle can be characterized as an opportunistic predator of such birds. Indicating that they are regarded as a threat to raptors is that they are frequently mobbed by a wide range of raptor species when displaying active flights, to a similar regard that the perhaps more aggressively predatory golden eagle is. Given the difficulty of this prey type, white-tailed eagles are likely to attack other birds of prey when the victims are distracted, whether by migration on windy days, nesting duties or when trying to capture their own prey, are previously injured or they may even capture one while the raptor tries to mob the eagle. Certainly, nestlings and fledglings can certainly comprise a large fraction of the birds of prey caught as well as adult ones. Other accipitrids they are known to have preyed upon, in increasing order of size are the Eurasian sparrowhawk ("Accipiter nisus"), western marsh harrier ("Circus aeruginosus"), black kite ("Milvus migrans"), European honey-buzzard ("Pernis apivorus"), common buzzard ("Buteo buteo"), northern goshawk, red kite ("Milvus milvus"), lesser spotted eagle ("Clanga pomarina") and eastern imperial eagle, in addition to osprey. Non-accipitrid raptorial birds, these more likely restricted to fully independent birds due to their less conspicuous nests, known to fall prey to white-tailed eagles include Eurasian pygmy owl ("Glaucidium passerinum"), boreal owl ("Aegolius funereus"), Eurasian hobby ("Falco subbuteo"), long-eared owl (Asio otus), northern hawk owl ("Surnia ulula"), short-eared owl ("Asio flammeus"), peregrine falcon ("Falco peregrinus"), snowy owl ("Bubo scandiacus") and Eurasian eagle owl ("Bubo bubo"). Accipitrid prey size ranges by body mass ranges from for a sparrowhawk to in the imperial eagle and that of non-accipitrid raptors ranges from for the pygmy owl to for the eagle owl and apparently both imperial eagles and eagle owls that were caught were adults. As true apex predators, healthy adult white-tailed eagles have no known natural predators.