Eurasian eagle-owl
Even those near the northern limits of their range, where winters are harsh and likely to bear little in food, the eagle-owl does not leave its native range. There are cases from Russia of Eurasian eagle-owls moving south for the winter, as the icebound, infamously harsh climate there is too severe even for these hardy birds and their prey. Similarly, Eurasian eagle-owls living in the Tibetan highlands and Himalayas may in some cases vacate their normal territories when winter hits and move south. Even in those two examples, there is no evidence of consistent, annual migration by Eurasian eagle-owls and the birds may eke out a living on their normal territories even in the sparsest times.
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 .