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The red-tailed hawk (''Buteo jamaicensis'') is a bird of prey, one of three species colloquially known in the United States as the "chickenhawk," though it rarely preys on standard sized chickens. It breeds throughout most of North America, from western Alaska and northern Canada to as far south as Panama and the West Indies, and is one of the most common buteos in North America. Red-tailed hawks can acclimate to all the biomes within their range. There are fourteen recognized subspecies, which vary in appearance and range. It is one of the largest members of the genus ''Buteo'' in North America, typically weighing from and measuring in length, with a wingspan from . The red-tailed hawk displays sexual dimorphism in size, with females averaging about 25% heavier than males.〔(【引用サイトリンク】title=Red-tailed Hawk )〕 The bird is sometimes referred to as the red-tail for short, when the meaning is clear in context. The subspecies Harlan's hawk (''B. j. harlani'') is sometimes considered a separate species (''B. harlani''). The red-tailed hawk occupies a wide range of habitats and altitudes, including deserts, grasslands, coniferous and deciduous forests, agricultural fields and urban areas. It lives throughout the North American continent, except in areas of unbroken forest or the high arctic. It is legally protected in Canada, Mexico and the United States by the Migratory Bird Treaty Act. Because they are so common and easily trained as capable hunters, the majority of hawks captured for falconry in the United States are red-tails. Falconers are permitted to take only passage hawks (which have left the nest, are on their own, but are less than a year old) so as to not affect the breeding population. Adults, which may be breeding or rearing chicks, may not be taken for falconry purposes and it is illegal to do so. Passage red-tailed hawks are also preferred by falconers because these younger birds have not yet developed the adult behaviors which would make them more difficult to train. == Description == As is the case with many raptors, the red-tailed hawk displays sexual dimorphism in size, as females are up to 25% larger than males.〔 As is typical in large raptors, frequently reported mean body mass for Red-tailed Hawks are somewhat higher than expansive research reveals. Part of this weight is highly seasonally variable and due to clinal variation, male red-tailed hawks may weigh from and in females between . However, research from nine studies occurring at migration sites in the United States and two breeding studies, one from the smallest race in Puerto Rico, the other from larger races in Wisconsin show that males weigh a mean of and females weigh a mean of , about 15% lighter than prior species-wide published weights.〔〔Preston, C. R. and R. D. Beane. (2009). ''Red-tailed Hawk (Buteo jamaicensis)'', The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online〕〔Snyder, N. F. R. and Wiley, J. W. (1976). ''Sexual size dimorphism in hawks and owls of North America''. Ornithological Monographs, No. 20, pp. i–vi, 1–96.〕 The heaviest surveyed weights came from migrants in Cape May, New Jersey, where females weighed a mean of , males a mean of .〔 The lightest were from the breeding population in forest openings of Puerto Rico, where the females and males weighed an average of and , respectively, also the highest size sexual dimorphism in the species. Size variation in body mass reveals that the red-tailed hawks typically varies only a modest amount, racial variation in average weights of great horned owls show that mean body mass is nearly twice (the heaviest race is about 36% heavier than the lightest known race on average) as variable as that of the hawk (where the heaviest race is only just over 18% heavier on average than the lightest).〔〔〔''CRC Handbook of Avian Body Masses'' by John B. Dunning Jr. (Editor). CRC Press (1992), ISBN 978-0-8493-4258-5.〕 Males can reportedly measure in total length, females measuring long. The wingspan can range from and, in the standard scientific method of measuring wing size, the wing chord is long. The tail measures in length.〔''Raptors of the World'' by Ferguson-Lees, Christie, Franklin, Mead & Burton. Houghton Mifflin (2001), ISBN 0-618-12762-3〕〔(Red-tailed Hawk videos, photos and facts ). Arkive.org. Retrieved 2012-08-22.〕 The exposed culmen was reported to range from and the tarsus averaged .〔〔 The middle toe (excluding talon) can range from , with the hallux-claw (the talon of the rear toe, which has evolved to be the largest in accipitrids) measuring from in length.〔〔 Red-tailed hawk plumage can be variable, depending on the subspecies and the region. These color variations are morphs, and are not related to molting. The western North American population, ''B. j. calurus'', is the most variable subspecies and has three color morphs: light, dark, and intermediate or rufus. The dark and intermediate morphs constitute 10–20% of the population.〔 Though the markings and hue vary across the subspecies, the basic appearance of the red-tailed hawk is consistent. Overall, this species is blocky and broad in shape, often appearing (and being) heavier than other ''Buteos'' of similar length.〔 A whitish underbelly with a dark brown band across the belly, formed by horizontal streaks in feather patterning, is present in most color variations. Especially in younger birds, the underside may be otherwise covered with dark brown spotting. The red tail, which gives this species its name, is uniformly brick-red above and light buff-orange below.〔〔 The bill is short and dark, in the hooked shape characteristic of raptors, and the head can sometimes appear small in size against the thick body frame.〔 They have a relatively short, broad tails and thick, chunky wings.〔(【引用サイトリンク】title=''Buteo jamaicensis'' )〕 The cere, the legs, and the feet of the red-tailed hawk are all yellow. Immature birds can be readily identified at close range by their yellowish irises. As the bird attains full maturity over the course of 3–4 years, the iris slowly darkens into a reddish-brown hue. In both the light and dark morphs, the tail of the immature red-tailed hawk is patterned with numerous darker bars.〔 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「Red-tailed hawk」の詳細全文を読む スポンサード リンク
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