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
A very large balance of the prey range can also be comprised by birds and other prey including reptiles, amphibians, fish, insects and other invertebrates are seemingly taken whenever they are available. All told, well more than 600 different species have been identified as prey of Eurasian eagle-owls. Their diet includes basically all the same prey as all sympatric diurnal raptors in the genera "Buteo", "Aquila" and "Haliaeetus". The total number of prey species may even surpass that of the great horned owl and may well be the greatest of any raptorial bird on the Eurasian continent. Among five segments of Europe the average prey diversity per region was 63 species, a higher number than any of the other 40 raptorial bird species studied there. The mean mass of prey per study has varied from as little as , near the now former Aral Sea in Turkmenistan with the Turkmen jerboa ("Jaculus turkmenicus") being the primary prey species, to , in Spain with the European rabbit being the primary prey species. Remarkably, in northern Spain, where the rabbit is now extirpated (as was the eagle-owl for a time in the 20th century), the average weight of prey can dip as low as . In comparison, the lightest mean prey mass in dietary studies of the great horned owl was while the highest was .