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.
Eurasian eagle-owl
The Eurasian eagle-owl has a very wide range across much of Europe and Asia, estimated to be about . In Europe there are estimated to be between 19,000 and 38,000 breeding pairs and in the whole world around 250,000 to 2,500,000 individual birds. The population trend is thought to be decreasing because of human activities, but with such a large range and large total population, the International Union for Conservation of Nature has rated the bird as being of "least concern". Although roughly equal in adaptability and wideness of distribution, the great horned owl, with a total estimated population of up to 5.3 million individuals, apparently has a total population that is roughly twice that of the Eurasian eagle-owl. Numerous factors, including a shorter history of systematic persecution, lesser sensitivity to human disturbance while nesting, somewhat greater ability to adapt to marginal habitats and widespread urbanization and slightly smaller territories, may play into the horned owls greater numbers in modern times.