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.
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).