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.
Eurasian eagle-owl
Long-eared owls in Eurasia have vertical striping like that of the Eurasian eagle-owl while long-eared owls in North America show a more horizontal striping like that of great horned owls. Whether these are examples of mimicry either way is unclear but it is known that both "Bubo" owls are serious predators of long-eared owls. The same discrepancy in underside streaking has also been noted in the Eurasian and American representations of the grey owl. A few other related species overlap minimally in range in Asia, mainly in east Asia and the southern reaches of the Eurasian eagle-owl’s range. Three fish owls appear to overlap in range, the brown ("Ketupa zeylonensis") in at least northern Pakistan, probably Kashmir and discontinuously in southern Turkey, the tawny ("K. flavipes") through much of eastern China and the Blakiston's fish owl in the Russian Far East, northeastern China and Hokkaido. Fish owls are distinctively different looking, possessing more scraggy ear tufts that hang to the side rather than sit erect on top of the head, generally have more uniform, brownish plumages without the contrasting darker streaking of an eagle-owl. The brown fish owl has no feathering on the tarsus or feet and the tawny has feathering only on the upper portion of the tarsi but the Blakiston’s is nearly as extensively feathered on the tarsi and feet as the eagle-owl. Tawny and brown fish owls are both slightly smaller than co-occurring Eurasian eagle-owls and Blakiston’s fish owls are similar or slightly larger than co-occurring large northern eagle-owls. Fish owls, being tied to the edges of freshwater where they hunt mainly fish and crabs, also have slightly differing, and more narrow, habitat preferences.