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The golden eagle (''Aquila chrysaetos'') is one of the most powerful predators in the avian world. One author described it as "the pre-eminent diurnal predator of medium-sized birds and mammals in open country throughout the Northern Hemisphere".〔(Cornell University ). Bna.birds.cornell.edu. Retrieved on 2012–08–22.〕 Golden eagles usually hunt during daylight hours, but were recorded hunting from one hour before sunrise to one hour after sunset during the breeding season in southwestern Idaho.〔Dunstan, T. C., Harper, J.H. & Phipps, K.B. 1978. ''Habitat use and hunting strategies of Prairie Falcons, Red-tailed Hawks, and Golden Eagles''. Fin. Rep. Western Illinois University, Macomb.〕 The hunting success rate of golden eagles was calculated in Idaho, showing that, out of 115 hunting attempts, 20% were successful in procuring prey. A fully-grown golden eagle requires about of food per day but in the life of most eagles there are cycles of feast and famine, and eagles have been known to go without food for up to a week and then gorge on up to at one sitting.〔 The powerful talons of the golden eagle ensure that few prey can escape them once contact is made. The talons of this species exert approximately of pressure, around 15 times more pressure than is exerted by the human hand, although some opine that the largest individual females may reach a pressure of .〔(Powerful feet and talons help birds of prey make their living | Lubbock Online | Lubbock Avalanche-Journal ). Lubbock Online (2006–03–26). Retrieved on 2012–08–22.〕 Few other large raptors have been tested in their foot strength, though the huge harpy eagle, when tested, exerted a psi approximately greater than the tested golden eagle.〔(【引用サイトリンク】title=Giant Harpy Eagle grabs the Sloth Video )〕 It has been claimed that the golden eagle can lift up to in flight.〔Terres, J. 1980. ''The Audubon society encyclopedia of North American birds''. Alfred A. Knophf, New York.〕 However, other sources claim that a hare, marmot or deer calf weighing () is a struggle for even a large female to carry and that prey much over would require favorably high wind conditions.〔Huey, M. 1962. ''Comparisons of the weight-lifting capacities of a House Finch and a Golden Eagle''. Auk, 79: 485.〕〔Kalmbach, E.R., Imler, R.H. & Arnold, L.W> 1964. ''The American Eagles and their Economic Status''. USDI, Fish and Wildlife Service, Washington.〕〔Snow, C. 1973. ''Golden Eagle Aquila chrysaetos. Habitat management of unique or endangered species''. USDI Bureau of Land Management Tech. Note 239.〕 == Hunting methods == At least seven main hunting techniques are known to be utilized by the species, with many individual variations and the ability in most mature eagles to quickly (and sometimes cleverly) vary back and forth between methods depending on the circumstance. The first described is “high soar with glide attack”, where the golden eagle soars at least above the earth. Once it spies a prey item, the eagle partially closes its wings and enters a long, low-angled glide which can carry it over distances of with the speed increasing as the wings close more. Just prior to impact, the wings are opened, the tail fanned and feet thrust forward to grab the prey, creating a booming sound, causing by the wings whipping against the wind, in the instant before the strike that sounds like a clap of thunder. This technique is used for solitary or widely dispersed prey found in openings, such as hares or ptarmigans. A variation of the high soar where a lofty perch is used instead of soaring flight has been observed.〔Carnie, S.K. 1954. ''Food habits of Golden Eagles in the coastal ranges of California''. Condor, 56: 3-12.〕 The next major hunting methods is the “high soar with vertical stoop”, which is used to attack birds in flight. Since they are outpaced and out-maneuvered by swift-flying birds, they can only usually attack slower-flying species such as geese and cranes. The golden eagle also requires a height advantage over their prey for this rarely observed technique to succeed. In one observed case, some Canada geese (''Branta canadensis'') in Montana were able to avoid predation by a golden eagle hunting them in this way by collectively gaining flying height.〔Cameron, E.S. 1908. ''Observations on the Golden Eagle in Montana''. Auk, 25: 251-268.〕 In another observation, a golden eagle was successful in knocking a ptarmigan out of a flying covey in Scotland.〔Meinertzhagen, R. 1940. ''How do larger raptorial birds hunt their prey?''. Ibis, 4: 530-535.〕 The next hunting method is the “contour flight with short glide attack”, which is considered the most commonly utilized hunting method for golden eagles. This consists of a low-level quartering flight often at only above the ground so they do not break the sky-line when observed from the ground and they can hug the contours of the earth below. This method is useful for hunting colonial (often burrowing) prey such as ground squirrels, densely populated leporids or birds found in concentrations, such as breeding grouse or even seabirds. The individual prey item is apparently selected in a manner of seconds before the strike.〔〔Dekker, D. 1985. ''Hunting behavior of Golden Eagle Aquila chrysaetos migrating in southwestern Alberta''. Canadian Field Naturalist, 49: 383-385.〕 If the first attempt fails, the eagle may fly around and attempt to ambush the prey again. The next hunting method is the “glide attack with tail-chase”, which commences with a low-angled stoop some distance from the quarry. The prey is then chased closely, whether a hare running evasively or a grouse in flight. The key to success is eagle's agility and the prey's inability to find cover. In one case, a flying greater sage-grouse (''Centrocercus urophasianus'') was caught by a pair of eagles using this technique.〔Bent, A.C. 1937. ''Life histories of North American Birds of Prey''. Part 1. U.S. National Museum Bulletin, 167: 1-109.〕 The next major hunting method is “low flight with slow descent attack”. In this, the golden eagle quarters low below the earth and then gradually swoops down on the prey. This is used for slow-moving prey, such as tortoises and hedgehogs, or any prey item with a general absence of escape behavior. This includes any potentially dangerous prey items, such as rattlesnakes and foxes.〔Grubac, B.R. 1988. ''The Golden Eagle in Southeastern Yugoslavia''. Lotus, 38/39: 95-135.〕 When hunting mammalian carnivores, the eagle may hover for some time over the potential prey and not press the attack unless the mammal looks down.〔〔 The next is the “low flight with sustained grip attack”, which is used for hunting ungulates. Here, the golden eagle flies over a herd of ungulates which in turn often huddle or break into a run. The eagle then selects it prey (typically young animals, though sometimes infirm or exceptionally healthy grown animals) and lands on prey's back or neck, talons gripping firmly, attempting to pierce vital organs or cause shock via a crushing grip to bone and cartilage. The hunting eagle typically rides its prey for several minutes with wings outstretched and flapping to maintain balance until the prey collapses, either as result of exhaustion, shock or internal injury.〔 The final major hunting method is the “walk and grab attack”, in which the eagle walks on the ground and attempts to pull its prey out of cover. This has been used for pulling jackrabbits out of brush but has even been utilized to grab the young of large prey (i.e. deer, sheep and badgers) literally right out from under their mother’s legs.〔〔Palmer, R.S. 1988. ''Golden eagle: Aquila chrysaetos''. In: Palmer RS (Ed.). ' 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Dietary biology of the golden eagle」の詳細全文を読む スポンサード リンク
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