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
Mammalian carnivores are potential competitors with golden eagles for food. Foxes may prey on the same species in a given area but, as they are occasionally hunted by the eagles and are mainly nocturnal, they tend to avoid direct conflicts. Though rare, golden eagles may sometimes pirate prey from various species of fox. In North America, coyotes ("Canis latrans") may engage in agonistic interactions with golden eagles. Despite being around three times as heavy, lone coyotes are seemingly dominated by golden eagles at many carrion or kill sites. In the Greater Yellowstone, golden eagles were ranked as the second most dominant scavenger at wolf kills during winter (when bears are hibernating) after coyote packs but above bald eagles. In one instance, a healthy adult male coyote was attacked and killed by a golden eagle. This coyote weighed after the eagle had consumed some of its internal organs. Conflicts between golden eagles and Scottish wildcats have been reported on rare occasions. In one instance, a golden eagle trying to hunt some wildcat kittens was intercepted by the mother wildcat. In the ensuing violent battle, the wildcat mother and the eagle both died. In Northern California, golden eagles have pirated lambs killed by bobcats, a species which has itself occasionally turned up in the eagle's diet. Per one anecdote from the Himalayas, a golden eagle reportedly tried to predaceously attack a snow leopard ("Panthera uncia") and was killed by the much larger felid, although this could have actually been a case of an overly bold eagle trying to displace a large predator from its own home range. Adult wolverines appear to be one of the few conspecific mammal carnivores to actively pose a threat to golden eagles. Wolverines were observed to prey on nestling golden eagles in Denali National Park. During incubation in Northern Sweden, an incubating adult golden eagle was killed on its nest by a wolverine. In Yellowstone National Park, one prey item amongst 473 recorded for cougars ("Puma concolor") was a golden eagle, although no details of the attack or of the age of the bird were reported. grizzly bear ("Ursus arctos horribilis") have also reportedly killed and eaten golden eagle nestlings in Denali National Park. The grizzly is reportedly one of the few mammals to trigger a strong aggressive reaction from the parent eagles when spotted close to the nest, as eagles have been observed to strike the bruins about the head and neck with their talons.