Dietary biology of the Eurasian eagle-owl
In rare cases, other predators may kill a Eurasian eagle-owl. In Europe, there is one case of a white-tailed eagle killing an eagle-owl and there are at least four known incidents of eagle-owls being killed by golden eagles. Also, an eagle-owl was found among the prey remains at a golden eagle eyrie in Mongolia. An eagle-owl was also found amongst the prey in the nest of steppe eagles ("Aquila nipalensis") in Altai Krai, Russia. In 2016, a large female subadult Bonelli's eagle ("Aquila fasciata") apparently preyed upon a three-year-old male Eurasian eagle-owl in Spain. Pine martens ("Martes martes") and stone martens ("Martes foina") are opportunistic nest predators. Although martens could probably reach most eagle-owl nests due to their agility and climbing abilities, they probably will attack nests when disturbance or low food supply result in lower nest attendance by the parent owls. Cases where nests have atypically been accessible on foot (for both humans and wild predators) have resulted in Eurasian eagle-owl nests being predated. Eurasian badgers, wild boars and raccoon dogs and raccoons, the latter two both where non-native in Germany, have also reportedly preyed on nests that they can access. In coastal areas of Spain, red foxes were reported to have preyed on four eagle-owls, including one unsexed brooding adult, at nests found to be reachable on foot by researchers. Cases of red foxes killing Eurasian eagle-owls at nests have reported elsewhere albeit very rarely, normally the eagle-owl is a greater danger to the foxes (and many of its other nest predators) than vice versa. In May 2017, a red fox was filmed killing two chicks and raiding the larder of an eagle-owl in Denmark.
Dietary biology of the Eurasian eagle-owl
While owls are apparently often killed by Eurasian eagle-owls while actively hunting, diurnal raptors are often ambushed at night at their large, conspicuous nests since they are easily located during hunting forays and the raptors are nearly defenseless in nocturnal conditions. The eagle-owl has been specified as the primary predator of common buzzards, peregrine falcons, common kestrel ("Falco tinnunculus") and black kites. The common buzzard and common kestrel are probably the most often selected diurnal raptors because they inhabit the edges most often hunted by the eagle-owls. Studies have shown that peregrine falcon experience lower productivity in areas where they nest closely to eagle-owls, as the eagle-owls pick off both nestlings and adults by night. However, peregrine populations were not hugely effected except in cases where small reintroductions were attempted of falcons or falcon populations were already rare due to other causes. The northern goshawk is itself a serious predator of other raptors. The eagle-owl is the goshawk's only major predator, although goshawks are not as intensely hunted as are buzzards due to their more deeply wooded preferred nesting habitat.