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Swainson's hawk (''Buteo swainsoni''), is a large ''Buteo'' hawk of the Falconiformes, sometimes separated in the Accipitriformes like its relatives. This species was named after William Swainson, a British naturalist. It is colloquially known as the grasshopper hawk or locust hawk, as it is very fond of Acrididae (locusts and grasshoppers) and will voraciously eat these insects whenever they are available. Their breeding habitat is prairie and dry grasslands in western North America. They build a stick nest in a tree or shrub or on a cliff edge. This species is a long-distance migrant, wintering in Argentina; it has been recorded as a vagrant in neighboring Chile, in the island countries of the Dominican Republic, and Trinidad and Tobago, and in Norway.〔 This species or its immediate predecessor is the ancestor of the Galápagos hawk, as demonstrated by recent research. The latter diverged from the mainland birds perhaps 300,000 years ago, a very short time in evolution.〔 ==Description== Swainson's hawk is a raptor and a medium-sized member of the ''Buteo'' genus. It broadly overlaps in size with the red-tailed hawk (''B. jamaicensis''), a related species found as a breeding resident almost throughout North America. Swainson's hawk is on average a little shorter in length, long, and weighs a bit less, .〔〔〔 However, Swainson's hawk has a slightly longer wingspan at , with more slender, elongated wings, than the red-tailed hawk.〔 Female Swainson's hawks, at an average weight of , are somewhat larger and heavier than males, at an average of .〔 Among standard measurements, the wing chord is , the tail is , the tarsus is and the bill (from the gape) is .〔 In flight, Swainson's hawk holds its wings in a slight dihedral; it tips back and forth slightly while soaring. There are two main color variations. Over 90% of individuals are light-morph; the dark morph is most common in the far west of the range:〔 * Light-morph adults are white on the underparts with a dark, reddish "bib" on the chest and a noticeable white throat and face patch. The underwings, seen as the bird soars, have light linings (leading edge) and dark flight feathers (trailing edge), a pattern unique among North American raptors. The tail is gray-brown with about six narrow dark bands and one wider subterminal band. The upperparts are brown. Juveniles are similar but dark areas have pale mottling and light areas, especially the flanks, have dark mottling. The chest is pale with some darker marks. The subterminal band of the tail is less obvious. Birds in their first spring may have pale heads because of feather wear. * Dark-morph birds are dark brown except for a light patch under the tail. There is a rufous variant that is lighter on the underparts with reddish bars. The tails of both these forms resemble those of the light morph. 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「Swainson's hawk」の詳細全文を読む スポンサード リンク
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