Dietary biology of the Eurasian eagle-owl
Throughout the western Mediterranean region, the Eurasian Eagle-Owl is something of a specialist on a single prey species: the European rabbit. The rabbit historically reached extremely high densities in Iberian scrub, i.e. more than 40 per every 1 square hectare (2471 square acres). In central Spain, up to 73.1% of the prey that were recorded for Eurasian eagle-owls, by number, can be rabbits. Where still available, they are also the main prey in Portugal and central France. However, following the devastation of the wild rabbit due to rabbit haemorrhagic disease, the local eagle-owls have frequently had to adapt to other, often smaller, prey. On the other hand, given the now much reduced numbers of rabbits, the eagle-owls still regularly select rabbits, seemingly out of proportion to their commonality. Although large mature wild rabbits commonly weigh , the eagle-owls usually hunt smaller specimens, often with an average weight around , with young rabbits usually selected in spring and summer and subadults selected in the autumn and winter. This is largely due to the behaviour of rabbits, with younger rabbits being forced to distribute following weaning, being less cautious in behaviour and occupying less primary habitat, thus being forced out of the confines of their burrows more regularly than mature adults. However, the estimated average weight of rabbits taken can be variable, reported from as little as in a study from Spain to as much as in the Netherlands.
Dietary biology of the Eurasian eagle-owl
Discreet habitat preferences may coincidentally spare many owls, as owls from the genera "Strix", "Glaucidium", "Aegolius" and the northern hawk-owl ("Surnia ulula") tend to restrict both nesting and their hunting forays to more enclosed areas of woodland than habitats inhabited by the eagle-owls. Meanwhile, "Asio", "Otus", "Athene" and barn owls owls tend to hunt in more open habitats than the edges favored by eagle-owls. However, habitat preferences are never enough to spare any of these genera from predation by the great eagle-owl. In the Italian Alps, despite differing habitat preferences and partially overlapping prey, several tawny owls were killed by eagle-owls. Woodland nesting owl species tend to nest in tree hollows, many of which are too small for an eagle-owl to access, so are somewhat less likely to be picked off at their nests. Open-country owls that tend to nest in open-access nesting sites like short-eared owls and little owls may be somewhat more vulnerable at the nest. The great numbers of long-eared owls taken, since it often nest in dense, protective thickets, are probably adult or immature owls attempting to hunt. In Europe, Eurasian eagle-owls are generally the only owls to regularly nest in rocky habitats. This is not the case in arid desert-like regions, where limited nesting options frequently force diverse owls to use rocky areas as nesting sites. However, the cliffs and other rocky areas preferred by Eurasian eagle-owls are also utilized by several species of diurnal raptor in Eurasia. In Spain, golden eagles, Bonelli's eagles and peregrine falcons ("Falco peregrinus") most often nest on cliffs. Large scavenging birds such as cinereous vultures ("Aegypius monachus"), bearded vultures ("Gypaetus barbatus"), Eurasian griffons ("Gyps fulvus"), Egyptian vulture ("Neophron percnopterus") and common ravens also often nests on the same Iberian cliffs. While the two eagles nested at great distances from one another (they are known to be territorial towards each other), the eagle-owl nesting within of the other species. In these cliff nests, the only considerable predatory interaction was the eagle-owls appearing to predate the peregrine falcons. In the Tibetan Plateau, upland buzzards ("Buteo hemilasius") also seem to favor similar habitats and both the eagle-owl and buzzard take similar prey there. In general, the eagle-owl can nest closer to diurnal raptors because, as a nocturnal animal, it will not actively compete for territories as it would with other members of its own species.