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
Eagle-owl has been singled out historically as a threat to game species and thus to the economic well-being of landowners, game-keepers and even governmental agencies and as such has been singled out for widespread persecution. Local extinctions of Eurasian eagle-owls have been primarily due to persecution. Examples of this including northern Germany in 1830, the Netherlands sometimes in the late nineteenth century, Luxembourg in 1903, Belgium in 1943 and central and western Germany in the 1960s. In trying to determine causes of death for 1476 eagle-owls from Spain, most were unknown and undetermined types of trauma. The largest group that could be determined, 411 birds, was due to collisions, more than half of which were from electrocution, while 313 were due to persecution and merely 85 were directly attributable to natural causes. Clearly, while pylon safety is perhaps the most serious factor to be addressed in Spain, persecution continues to be a massive problem for Spanish eagle-owls. Of seven European nations where modern Eurasian eagle-owl mortality is well-studied, continual persecution is by far the largest problem in Spain, although also continues to be serious (often comprising at least half of studied mortality) in France. From France and Spain, nearly equal numbers of eagle-owls are poisoned (for which raptors might not be the main target), or shot intentionally.