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.
Dietary biology of the golden eagle
The estimated typical range of weights of hares hunted by golden eagles is , whereas rabbits hunted weigh a little under on average. Except for the occasional Arctic hare, white-tailed or antelope jackrabbit ("Lepus alleni"), most leporids hunted in North America weigh or less, including the smallest hare in the world, the snowshoe hare, and the smallest rabbit in the world, the pygmy rabbit ("Brachylagus idahoensis"). In Europe, where the large brown and mountain hares, both sometimes weighing over , are habitually hunted, the prey may be dismembered before being brought to the nest. Across the golden eagle's range, hares and rabbits are generally known to be hunted via either "high soar with glide attack" or "contour flight with short glide attack". Leporids are basically solitary animals but they can occur at high densities, such as when jackrabbits are at their peak numbers in brushy areas of Western North America or (historically at least) rabbits in similar brush habitats on the Iberian Peninsula. The goal of the golden eagle while hunting hares and rabbits is to catch the prey when it is foraging out in the open. If the leporid becomes aware of the eagle's descent upon them more than a few seconds before the strike, they invariably break into a fast, hopping run. Once contact is made, rabbits and hares will often kick or try to bite the eagle but escape is unlikely once they are pinned to the ground. In some case they are able to reach vegetative coverage and, if the said cover is sufficiently deep and dense, the eagle cannot pursue them any further. Although rare, golden eagles have been known to use the "walk and grab attack" to pull a leporid out of its cover. Many hunts in Scotland of mountain hare involve a somewhat lengthy tail chase. If the golden eagle is able to intercept a rabbit or hare far out in the open, a twisting and turning tail chase frequently occurs but the odds of survival for the prey are smaller the farther they are from coverage. On occasion, breeding pairs have been observed hunting jackrabbits together, where one will stoop on a gathering of them while the other waits out of sight and assaults one of the jackrabbits being made to run.