Dietary biology of the golden eagle
Owls, which may have dissimilar periods of activity, are not entirely exempt from golden eagle predation either. Several species have been recorded as prey, especially in Northern Europe, Slovakia (where owls make up 2.4% of prey remains) and some parts of the Western United States. Species hunted have ranged in size from tiny Eurasian pygmy owl ("Glaucidium passerinum") and little owl ("Athene noctua") to the formidable, large great horned, Eurasian eagle and great gray owls ("Strix nebulosa"). Barn owls ("Tyto alba") have been predated by golden eagles in both North America and Eurasia. On Santa Rosa and Santa Cruz Islands, barn owls made up 4.5% of the diet, the largest known occurrence of that species in the eagles' diet. However, the great horned owl is the owl species that occurs most regularly in the diet of North American golden eagles. In Europe, golden eagles are relatively minor predators of owls compared to Eurasian eagle-owls and northern goshawks. The primary owls hunted by European eagles are Ural owls ("Strix uralensis") and short-eared owls ("Asio flammeus"). Few eye-witness accounts are known of owl predation, but one violent mid-day confrontation between a golden eagle and an adult great horned owl was witnessed in Jefferson County, Colorado. Although this owl was about a third of the eagle's weight, it was able to land some damaging blows on the larger bird. In the end, despite its wounds, the eagle was victorious over the dead owl. A case of kleptoparasitism by a golden eagle on a great horned owl has been recorded. Although the Eurasian eagle-owl is preyed upon by golden eagles (4 confirmed cases of golden eagles killing eagle-owls in Europe), in one case a golden eagle (age unspecified) was found amongst the prey in an eagle-owl nest.
Dietary biology of the Eurasian eagle-owl
Jirds, jerboas, gerbils and hamsters, particular the genera "Allactaga", "Ellobius", "Gerbillus", "Meriones", and "Pygeretmus", start to become noticeable in the diet in the more arid portions of this species’ range, i.e. from Asia Minor to the Middle East and Central Asia. Relatively large species such as Tristram's jird ("Meriones tristrami") and the Euphrates jerboa ("Allactaga euphratica") are often amongst the more prominent species to be hunted. In western Kazakhstan, the primary foods are the great jerboa ("Allactaga major") and northern mole vole ("Ellobius talpinus") while on the Buzachi and Mangyshlak Peninsulas of the Kazakh Caspian Sea, the primary foods were the Libyan jird ("Meriones libycus"), great gerbil ("Rhombomys opimus") and small five-toed jerboa ("Allactaga elater"). All told, in the peninsular Kazakh regions of the Caspian Sea, jirds, jerboas and gerbils made up about 92% of the food. In the Tibetan Plateau of China, the tundra vole ("Microtus oeconomus") is the leading prey species, making up 53.1% of the prey. In Mongolia, two rather small rodents, the Mongolian five-toed jerboa ("Allactaga sibirica"), at 23.6% of the prey, and the Campbell's dwarf hamster ("Phodopus campbelli"), at 14.5% of the prey, make up a majority of the prey by number. In the Transbaikal, the Chinese striped hamster ("Cricetulus barabensis") was the main prey species, making up 43.8% of the diet.
What all primary rodent prey species share is that they are either nocturnal or crepuscular and are often common to abundant in openings of woods and rocky environments. The reason Eurasian eagle-owls take rats, which associate rather closely with humans, much more regularly than they take house mice ("Mus musculus") is not their larger size (many other rodents regularly taken by eagle-owls are as small or smaller than a house mouse) but the rat's ability to flourish along the edges of crop fields, refuse dumps, roadsides and abandoned buildings and fields, whereas the mice are more closely tied to active human habitations. A single refuse dump can host several thousand rats and eagle-owl territories that include dumps can locally expect higher productivity due to the abundance of this food source. Squirrels are readily predated but, being diurnal, are largely unavailable to this and other owls. When they are captured, it is presumably around dawn or dusk from their tree hole, in species such as the widespread red squirrel ("Sciurus vulgaris"), or burrow entrance, in the case of ground squirrels, most regularly recorded as prey in Asia Minor and the Central Asia. A few specimens of the woolly flying squirrels ("Eupetaurus cinereus"), the largest of the world's flying squirrels and one of the rarest, were the only identified foods for Eurasian eagle-owls in northern Pakistan alongside some European hares. Although not common in the diet, a few species of marmot have been taken and may be an important aspect of the prey biomass. In Europe, adult-sized alpine marmots, ("Marmota marmota") have been killed. However, the average weight of Tarbagan marmots ("Marmota sibirica") taken in Mongolia was only and that of alpine marmots in Engadin, Switzerland was only . These obviously comprising young marmots as adults have average weights from , from spring low weights to pre-hibernation weights during autumn hypophagia. Other than marmots, the largest rodent known to be hunted by Eurasian eagle-owls is the introduced aquatic rodents, the muskrat ("Ondatra zibethica"), which in one study estimated to average when taken, and the nutria ("Myocastor coypus"), equal in size to the large marmots.