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
Eurasian eagle-owls are strictly territorial and will defend their territories from interloping eagle-owls year around, but territorial calling appears to peak around October to early January. Territory size is similar or occasionally slightly greater than great horned owl: averaging . Territories are established by the male eagle-owl, who selected the highest points in the territory from which to sing. The high prominence of singing perches allows their song to be heard at greater distances and lessens the need for potentially dangerous physical confrontations in the areas where territories may meet. Nearly as important in territorial behaviour as vocalization is the white throat patch. When taxidermied specimens with flared white throats were placed around the perimeter of eagle-owl territories, male eagle-owls reacted quite strongly and often attacked the stuffed owl, reacting more mildly to a stuffed eagle-owl with a non-flared white throat. Females were less likely to be aggressive to mounted specimens and did not seem to vary in their response whether exposed to the specimens with or without the puffed up white patch. In January and February, the primary function for vocalization becomes for the purpose of courtship. More often than not, eagle-owls will pair for life but usually engage in courtship rituals annually, most likely to re-affirm pair bonds. When calling for the purposes of courtship, males tend to bow and hoot loudly but do so in a less contorted manner than the male great horned owl. Courtship in the Eurasian eagle-owl may involve bouts of "duetting", with the male sitting upright and the female bowing as she calls. There may be mutual bowing, billing and fondling before the female flies to a perch where coitus occurs, usually taking place several times over the course of a few minutes.