Eurasian eagle-owl
The Eurasian eagle-owl is a member of the genus "Bubo", which may include either 22 or 25 extant species. Almost all the larger owl species in the world today are included in "Bubo". Based on an extensive fossil record and a central distribution of extant species on that continent, the "Bubo" appears to have evolved into existence in Africa, although early radiations seem to branch from southern Asia as well. Two genera belonging to the scops owls complex, the giant scops owls ("Otus gurneyi") found in Asia and the "Ptilopsis" or the white-faced scops owl found in Africa, although firmly ensconced in the scops owl group, appear to share some characteristics with the eagle-owls. The "Strix" is also related to the "Bubo" and is considered a "sister complex", with the "Pulsatrix" possibly being intermediate between the two. The Eurasian eagle-owl appears to represent an expansion of the genus "Bubo" into the Eurasian continent. A few of the other species of "Bubo" seem to have been derived from the Eurasian eagle-owl, making it a "paraspecies", or they at least share a relatively recent common ancestor. The Pharaoh eagle-owl, distributed in the Arabian Peninsula and sections of the Sahara Desert through North Africa where rocky outcrops are found, was until recently considered a subspecies of the Eurasian eagle-owl. It appears that the Pharaoh eagle-owl differs about 3.8% in mitochondrial DNA from the Eurasian eagle-owl, well past the minimum genetic difference to differentiate species of 1.5%. Smaller and paler than Eurasian eagle-owls, the Pharaoh can also be considered a distinct species largely due to its higher pitched and more descending call and the observation that Eurasian eagle-owls formerly found in Morocco ("B. b. hispanus") apparently did not breed with the co-existing Pharaoh eagle-owls. On the contrary, the race still found together with the Pharaoh eagle-owl in the wild ("B. b. interpositus") in the central Middle East has been found to interbreed in the wild with the Pharaoh eagle-owl, although genetical materials have indicated "interpositus" may itself be a distinct species from the Eurasian eagle-owl, as it differs from the nominate subspecies of the Eurasian eagle-owl by 2.8% in mitochondrial DNA. The Indian eagle-owl was also considered a subspecies of Eurasian eagle-owl until recently, but its smaller size, distinct voice (more clipped and high-pitched than Eurasians), and the fact that it is largely allopatric in distribution (filling out the Indian subcontinent) with other Eurasian eagle-owl races has led to it being considered a distinct species. The mitochondrial DNA of the Indian species also appears considerably distinct from the Eurasian species. The Cape eagle-owl ("B. capensis") appears to represent a return of this genetic line back into the African continent, where it leads a lifestyle similar to northern eagle-owls albeit far to the south. Another offshoot of the northern "Bubo" group is the snowy owl. It appears to have separated from other "Bubo" at least 4 million years ago.
Dietary biology of the Eurasian eagle-owl
In terms of sheer quantitative abundance, rodents are by far the most dominant prey group in the diet of the Eurasian eagle-owl. Roughly 130 species of rodent are known to have been taken by these owls. Due to their small sizes, however, rodent prey often comprise a relatively small portion of the prey biomass, excepting relatively large rodents such as rats and hamsters, some of which weigh at least . In many parts of Europe, the most numerous prey in dietary studies are the brown rat and the common vole, followed by the nearly as widespread field vole ("Microtus agrestis"). Among the areas where the common vole was the leading prey species included southern Sweden, Germany, Poland, the Czech Republic, and Slovakia. In areas that have undergone more heavy development, the brown rat predominates, being the leading prey item in several parts of France including Côte-d'Or, Lozère and even the remote Pyrenees, Belgium, the Italian Alps, and Brașov, Romania. The brown rat is even the primary prey in Lebanon despite it being tied solely to human habitations as the environment is often too arid to allow it to survive further afield. Black rats ("Rattus rattus"), at , are also hunted but rarely in equal number to the generally more successful brown rats. In Norway and Finland, field voles were the most numerous prey species, per one study in the latter country it made up 30.1% of the food but only provided 3.3% of the prey biomass. The European water vole, averaging at , was the main prey species in Styria, Austria, although considerably secondary in biomass to hedgehogs, as well as in central Sweden. The water vole often the second or third most regularly found prey species in several other European studies. In Samara, Russia, the diet is dominated by the European water vole, although other species such as European hamsters ("Cricetus cricetus") and European hares ("Lepus europaeus") (both also significant prey there) probably outweigh them in biomass contribution. The common vole and European water vole together made up roughly 80% of the prey by number in the High Tatras of Slovenia and more than 60% of the diet in bordering Poland.
In the northern extremes of their range, Eurasian eagle-owls tend to have a less varied diet than those to the south and the need to catch significant numbers of rodents rises as they are often the only regularly accessible prey in sparse sub-Arctic environments. In northern Sweden, more than 60% of the food was made up of microtine rodents, i.e. the Norway lemming ("Lemmus lemmus"), the field vole, the European water vole and the grey red-backed vole ("Myodes rufocanus"). In one study from western Russia, rodents comprised more than 90% of the diet of the eagle-owls, led by the steppe lemming ("Lagurus lagurus") at 24% by number, the narrow-headed vole ("Microtus gregalis") at 21% and the European water vole at 17.9%. Similarly in high altitude tundra of the East Austrian Alps, nearly 90% of the food was found to be comprised by microtine rodents, the European snow vole ("Chionomys nivalis") being the most frequently identified species in the diet. In Spain, the Algerian mouse ("Mus spretus"), at up to 41.8% of the prey by number, and wood mouse ("Apodemus sylvaticus"), at up to 10.5% by number, are often regularly taken, especially in regions where rabbit numbers have declined. In Romania, the Romanian hamster ("Mesocricetus newtoni") and European hamster are the most prominent species found in the eagle-owl's diet, alongside the brown rat. The Romanian hamster is also dominated the prey list per a study in Bulgaria, only the European water vole follows distantly in number. Dormice are readily taken when available in Europe, especially the edible dormouse from central Europe to the eastern countries. In Slovenia, the edible dormouse was the most regularly-recorded prey species, making up 20.2% of the food but it comprised 9.4% of the biomass. The edible dormouse was also the most regular prey species in Trentino-Alto Adige/Südtirol, Italy, making up 22.5% of the diet. The smaller garden dormouse ("Eliomys quercinus") and considerably smaller hazel dormouse ("Muscardinus avellanarius") are also occasionally predated in Europe, plus at least a half dozen other dormouse species in eastern Europe, Asia Minor and several points to the east.