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''Crex'' is a small genus of birds in the rail family. It contains two species, the corn crake, ''C. crex'', which breeds across Europe and Asia and winters in southern Africa, and the African crake, ''C. egregia'', which migrates within Africa. Both are short-billed rails with blackish-brown upperparts, mainly blue-grey underparts, and barring on the flanks. The corn crake is significantly larger than its relative, and has a distinctive chestnut patch on its wings. Unusually for their family, these are birds of dry habitats rather than wetlands; the Eurasian species mainly breeds in hay meadows, and the African crake in dry grassland. The African crake is sometimes given its own genus, ''Crecopsis'', but is now more usually placed in ''Crex''. Both species have distinctive loud grating calls used for advertising and territorial purposes in the breeding season, although the corn crake is silent on its African wintering grounds. They are mainly active during the day; they walk with a high-stepping action, and when disturbed they can run swiftly through grass or fly a short distance to cover. Migration takes place at night, and the ability to undertake these journeys is innate, not learned from adults. The nest is a shallow cup of grass lined with finer vegetation and built in a well hidden depression. The precocial chicks leave the nest soon after hatching, and fledge after four to six weeks. These are ground-feeding omnivores, but mainly eat invertebrates. They may be killed by a variety of mammals and large birds, and infected by parasites. The two ''Crex'' species have huge breeding ranges and large populations and are classed as least concern on the IUCN Red List. The corn crake was formerly classified as near-threatened because of serious declines in western Europe, but improved monitoring shows that numbers have remained stable further east in Russia and Kazakhstan. In much of the western half of the corn crake's breeding range, there have been long-term declines that are expected to continue. The main cause of the decline is the loss of nests and chicks from early mowing. Haymaking dates have moved forward in the past century due to faster crop growth, made possible by land drainage and the use of fertilisers, and the move from manual grass-cutting using scythes to mechanical mowers. Loss of habitat is the other major threat to the corn crake. Drained and fertilised silage fields are less suitable for breeding than traditional hay meadows. In western Europe the conversion of grassland to arable land has been aided by subsidies, and further east the collapse of collective farming has led to the abandonment and lack of management of much land in this important breeding area. == Taxonomy == The rails are a bird family comprising nearly 150 species. Although the origins of the group are lost in antiquity, the largest number of species and the most primitive forms are found in the Old World, suggesting that this family originated there. The genus ''Crex'' was created by German naturalist and ornithologist Johann Matthäus Bechstein in 1803.〔 Originally it held only the corn crake, ''C. crex'', which Bechstein moved from its original name, ''Rallus crex'', given to it by Linnaeus in his ''Systema Naturae'' in 1758. The taxonomy of the small crakes is complicated, but the closest relative of the corn crake is the African crake, ''C. egregia''. This was first described as ''Ortygometra egregria'' by Wilhelm Peters in 1854 from a specimen obtained in Mozambique, and has variously been placed in the genus ''Porzana'' or its own genus, ''Crecopsis'', but is now more usually placed in ''Crex''.〔Taylor & van Perlo (2000) p. 30〕〔Livezey (1998) p. 2098〕 The ''Porzana'' crakes are the closest relatives of the ''Crex'' genus, particularly the ash-throated crake, ''Porzana albicollis'', which has occasionally also been allocated to ''Crex''.〔Livezey (1998) p. 2134〕 The genus name is onomatopoeic, referring to the repetitive grating call of the corn crake. Although these species occur in fairly open habitats, they lack the pure white undertail used for signalling in open-water or gregarious species like the coots and moorhens.〔 〕 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「Crex」の詳細全文を読む スポンサード リンク
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