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
Wild birds found in their diet have ranged in size from the Eurasian wren ("Troglodytes troglodytes") to about 15 species weighing over . One of the largest wild adult bird verified as prey was the greylag goose ("Anser anser"). Other large species have been hunted, some may be cases of nest robbery rather than large adults but none are heavier than the largest mammalian prey that eagle-owls have taken including greater white-fronted goose ("Anser albifrons"), bar-headed goose ("Anser indicus"), great cormorant ("Phalacrocorax carbo"), Himalayan snowcock ("Tetraogallus himalayensis") and demoiselle crane ("Anthropoides virgo"), all averaging around , the swan goose ("Anser cygnoides"), the common crane ("Grus grus") and the (between the dimorphic sexes) great bustard ("Otis tarda"). Eurasian eagle-owls have also hunted adult male western capercaillie, which average about , although usually the much smaller females, at , are more regularly taken. Although they rarely take domestic birds, the range of sizes killed is just as dramatic, from loose budgerigars ("Melopsittacus undulatus"), weighing only , to domestic turkeys, which may easily weigh over .