Dietary biology of the Eurasian eagle-owl
In the Iberian peninsula, the Eurasian eagle-owl is part of a complex guild of predators that have evolved to survive mostly on European rabbits. Among this guild, golden eagles ("Aquila chrysaetos") were recorded per one study to rely on rabbits for 40% of the diet, the eagle-owl for 49% of the diet, the Spanish imperial eagle ("Aquila adalberti") for 50% of the diet, the Bonelli's eagle ("Aquila fasciata") for 61% of the diet and the Iberian lynx ("Lynx pardinus") for 79% of the diet. Elsewhere, the Spanish imperial eagle and eagle-owl are considered to outflank the golden and even the Bonelli's eagle as the most specialized avian predator of rabbits in the Iberian region. Other predators, such as common buzzard ("Buteo buteo"), northern goshawk ("Accipiter gentilis") black kite ("Milvus migrans") Iberian wildcat ("Felis silvestris tartessia"), red fox, stone marten ("Martes foina") and introduced Egyptian mongoose also prey heavily on rabbits in Spain, but are more generalized and less reliant than the above predators. All these powerful predators do not generally compete directly for food but conflicts may ensue over the rights to territories and nesting sites amongst the birds. Being nocturnal in activity, however, the Eurasian eagle-owl does not tend to compete as directly as do the three eagle species and even these are discreetly segregated by habitat preferences, the goldens preferring open, steep cliffs, the Bonelli's favoring densely vegetated areas mixed with rocky spots and the imperial favoring relatively flat open woodlands. Among these eagles, the golden eagle tends to have the most similar habitat preferences to the Eurasian eagle-owl and across a broad band of overlapping distribution, the two are considered nearly ecological equivalents by day and night. However, good-sized female golden eagles are up to twice as heavy as an average eagle-owl, so seem to have a considerable advantage in size and power. Conversely, to support their large size and large territory needs, the golden eagle cannot survive on small and diverse prey nearly as successfully as the eagle-owl. Among the Iberian peninsula rabbit-eating guild, the species with wider ranges, the eagle-owl and the golden and Bonelli's eagles, have had some degree of success living off of alternate prey following the devastation of the rabbit population due to rabbit haemorrhagic disease. The two rabbit predators endemic to Iberia, the Iberian lynx and Spanish imperial eagle, have been devastated by the reduction and other causes and both are threatened species today.
Eurasian eagle-owl
The Eurasian eagle-owl is largely nocturnal in activity, as are most owl species, with its activity focused in the first few hours after sunset and the last few hours before sunrise. In the northern stretches of its range, partial diurnal behaviour has been recorded, including active hunting in broad daylight during the late afternoon. In such areas, full nightfall is essentially non-existent at the peak of summer, so eagle-owls must presumably hunt and actively brood at the nest during daylight. The Eurasian eagle-owl has a number of vocalizations that are used at different times. It will usually select obvious topographic features such as rocky pinnacles, stark ridges and mountain peaks to use as regular song posts. These are dotted along the outer edges of the eagle-owl’s territory and they are visited often but only for a few minutes at a time. Vocal activity is almost entirely confined to the colder months from late fall through winter, with vocal activity in October through December mainly having territorial purposes and from January to February being primarily oriented towards courtship and mating purposes. The territorial song, which can be heard at great distance, is a deep resonant "ooh-hu" with emphasis on the first syllable for the male, and a more high-pitched and slightly more drawn-out "uh-hu" for the female. It is not uncommon for a pair to perform an antiphonal duet. The widely used name in Germany as well as some other sections of Europe for this species is "uhu" due to its song. At 250–350 Hz, the Eurasian eagle-owls territorial song or call is deeper, farther-carrying and is often considering "more impressive" than the territorial songs of the great horned owl or even that of the slightly larger Blakiston’s fish owl, although the horned owl’s call averages slightly longer in duration. Other calls include a rather faint, laughter-like "OO-OO-oo" and a harsh "kveck-kveck". Intruding eagle-owls and other potential dangers may be met with a "terrifying", extremely loud "hooo". Raucous barks not unlike those of ural owls or long-eared owls have been recorded but are deeper and more powerful than those species’ barks. Annoyance at close quarters is expressed by bill-clicking and cat-like spitting, and a defensive posture involves lowering the head, ruffling the back feathers, fanning the tail and spreading the wings.