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.
Red-tailed hawk
In turn, red-tailed hawks may engage in behavior that straddles territorial exclusion and anti-predator behavior to the two much larger raptors in North America which actively hunt, the eagles. Red-tails are most commonly seen flying towards and aggressively displacing both flying bald eagles ("Haliaeetus leucocephalus") and golden eagles ("Aquila chrysaetos"), but may also, to the contrary, unobtrusively duck down out of flight to an inconspicuous perch when an eagle is spotted. The behavioral variation is probably related to the activity of hawks, which may feel the need to protect their nests and food resources while actively breeding but are not usually willing to risk their lives in attacking an eagle while migrating or wintering. At times mobbing behavior of smaller raptors may cause both eagles to turn over and present their large talons to their attacker, which can be dangerous for the smaller hawk. Besides the great horned owl, the two eagle species are the only known animals known to regularly threaten red-tailed hawks of any age. In particular, the golden eagle is probably the greatest daytime threat to fledged immature and adult red-tails, as these have turned up in many dietary studies of the powerful eagle. Less efficient as a predator of red-tails, bald eagles nonetheless have been recording killing adults in some cases or, more often, depredating red-tailed hawk nests. On occasion, this may result in the bald eagle bringing the nestling red-tails to their own nest and, for some reason, not killing them. In some cases, the bald eagles inadvertently actually raise the nestling red-tails themselves and the baby red-tailed hawks may successfully fledge. In one case, a red-tailed hawk was observed to kill a bald eagle chick, whether this was predatory or competitive, it quickly abandoned the dead nestling after the eagle’s parents returned. On several tropical islands, which are often shared only with other hawks, owls and falcons of only medium or small size and typically lack larger raptors or carnivorans, the red-tailed hawk may be the largest native predator and will, in these cases, be considered the apex predator. Other than large birds of prey, extensive records of predation on red-tailed hawks is surprisingly poor, in spite of several populations recording nestlings and eggs disappearing through presumed acts of natural predation. The most likely major predator of eggs and nestlings that disappear is the raccoon which, during its nocturnal foraging, is a notorious enemy of nearly any kind of birds nest. It is also known that unidentified large snakes, probably consisting of the same species that the red-tails so readily predate during broad daylight, will prey upon nestling red-tails. In California, common ravens were recorded preying on the downy young of red-tailed hawks. Other corvids, including blue jays ("Cyanocitta cristata"), California scrub jays ("Aphelocoma californica") and crows, are known to feed on eggs and small nestlings either when nest attendance is atypically low by the hawks or when they can successful harass the parent hawks via mobbing so severely that they temporarily leave the nest. Blackflies ("Simulium canonicolum") have been recorded as killing several red-tail chicks through blood loss. There are also several cases of possible prey turning the tables on red-tailed hawks and either maiming or killing them. This is especially true of snakes, with some prey species of "Pituophis", "Pantherophis" and "Coluber" known to overpower and nearly kill, often the hawk survives only if by human intervention. Not infrequently prey such as coral snakes and rattlesnakes may succeed in killing red-tailed hawks with their venom, even if they themselves are also killed and partially consumed. Peregrine falcons are also known to kill red-tailed hawks that have come too close to their nests by stooping upon them.