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.
Eurasian eagle-owl
The Eurasian eagle-owl is a very large bird, smaller than the golden eagle ("Aquila chrysaetos") but larger than the snowy owl, despite some overlap in size with both species. It is sometimes referred to as the world's largest owl, although Blakiston's fish owl ("B. blakistoni") is slightly heavier on average and the much lighter weight great grey owl ("Strix nebulosa") is slightly longer on average. Heimo Mikkola reported the largest specimens of eagle-owl as having the same upper body mass, , as the largest Blakiston’s fish owl and attained a length of around longer. In terms of average weight and wing size, the Blakiston’s is the slightly larger species seemingly, even averaging a bit larger in these aspects than the biggest eagle-owl races from Russia. Also, although shorter than the largest of the latter species, the Eurasian eagle-owl can weigh well more than twice as much as the largest great grey owl. The Eurasian eagle-owl typically has a wingspan of , with the largest specimens possibly attaining . The total length of the species can vary from . Females can weigh from and males can weigh from . In comparison, the barn owl ("Tyto alba"), the world's most widely distributed owl species, weighs about 500 g (1.1 lb) and the great horned owl ("Bubo virginianus"), which fills the eagle-owl's ecological niche in North America, weighs around 1.4 kg (3.1 lb).