Corn Crake

识别特征

The corn crake is a medium-sized rail, 27–30 cm (11–12 in) long with a wingspan of 42–53 cm (17–21 in). Males weigh 165 g (5.8 oz) on average and females 145 g (5.1 oz). The adult male has the crown of its head and all of its upperparts brown-black in colour, streaked with buff or grey. The wing coverts are a distinctive chestnut colour with some white bars. The face, neck and breast are blue-grey, apart from a pale brown streak from the base of the bill to behind the eye, the belly is white, and the flanks, and undertail are barred with chestnut and white. The strong bill is flesh-coloured, the iris is pale brown, and the legs and feet are pale grey. Compared to the male, the female has warmer-toned upperparts and a narrower duller eye streak. Outside the breeding season, the upperparts of both sexes become darker and the underparts less grey. The juvenile is like the adult in appearance, but has a yellow tone to its upperparts, and the grey of the underparts is replaced with buff-brown. The chicks have black down, as with all rails. While there are no subspecies, all populations show great individual variation in colouring, and the birds gradually become paler and greyer towards the east of the range. Adults undergo a complete moult after breeding, which is normally finished by late August or early September, before migration to south eastern Africa. There is a pre-breeding partial moult prior to the return from Africa, mainly involving the plumage of the head, body and tail. Young birds have a head and body moult about five weeks after hatching.<p>The corn crake is sympatric with the African crake on the wintering grounds, but can be distinguished by its larger size, paler upperparts, tawny upperwing and different underparts pattern. In flight, it has longer, less rounded wings, and shallower wingbeats than its African relative, and shows a white leading edge to the inner wing. In both the breeding and wintering ranges it is unlikely to be confused with any other rails, since sympatric species are smaller, with white markings on the upperparts, different underparts patterns and shorter bills. A flying corn crake can resemble a gamebird, but its chestnut wing pattern and dangling legs are diagnostic.<p>On the breeding grounds, the male corn crake's advertising call is a loud, repetitive, grating krek krek normally delivered from a low perch with the bird's head and neck almost vertical and its bill wide open. The call can be heard from 1.5 km (0.93 mi) away, and serves to establish the breeding territory, attract females, and challenge intruding males. Slight differences in vocalisations mean that individual males can be distinguished by their calls. Early in the season, the call is given almost continuously at night, and often during the day, too. It may be repeated more than 20,000 times a night, with a peak between midnight and 3 am. The call has evolved to make a singing male's location clear, as this species hides in vegetation. The frequency of calling reduces after a few weeks but may intensify again near the end of the laying period before falling away towards the end of the breeding season. To attract males, mechanical imitations of their call can be produced by rubbing two pieces of wood or ribs, one of them with notches, or by flicking a credit card against a comb or zip-fastener. The male also has a growling call, given with the bill shut and used during aggressive interactions.<p>The female corn crake may give a call that is similar to that of the male; it also has a distinctive barking sound, similar in rhythm to the main call but without the grating quality. The female also has a high-pitched cheep call, and a oo-oo-oo sound to call the chick. The chicks make a quiet peeick-peeick contact call, and a chirp used to beg for food. Because of the difficulty in seeing this species, it is usually censused by counting males calling between 11 pm and 3 am; the birds do not move much at night, whereas they may wander up to 600 m (660 yd) during the day, which could lead to double-counting if monitored then. Identifying individual males suggests that just counting calling birds underestimates the true count by nearly 30%, and the discrepancy is likely to be greater, since only 80% of males may call at all on a given night. The corn crake is silent in Africa.

分类信息

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 least specialised forms are found in the Old World, suggesting this family originated there. The taxonomy of the small crakes is complicated, but the closest relative of the corn crake is the African crake, which has been given its own genus, Crecopsis.<p>Corn crakes were first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae as Rallus crex, but was subsequently moved to the genus Crex, created by German naturalist and ornithologist Johann Matthäus Bechstein in 1803, and named Crex pratensis. The earlier use of crex gives it priority over Bechstein's specific name pratensis, and leads to the current name of Crex crex. The binomial name, Crex crex, from the ancient Greek "κρεξ", is onomatopoeic, referring to the crake's repetitive grating call. The common name was formerly spelt as a single word, "corncrake", but the official version is now "corn crake". The English names refer to the species' habit of nesting in dry hay or cereal fields, rather than marshes used by most members of this family.

学名

Crex crex

命名信息

(Linnaeus, 1758)

目

Gruiformes

科

Rallidae

属

Crex

分布与栖息地

The corn crake breeds from Ireland east through Europe to central Siberia. Although it has vanished from much of its historic range, this bird was once found in suitable habitats in Eurasia everywhere between latitudes 41°N and 62°N. There is also a sizable population in western China, but this species nests only rarely in northern Spain and in Turkey. Old claims of breeding in South Africa are incorrect, and result from misidentification of eggs in a museum collection which are actually those of the African rail.<p>The corn crake winters mainly in Africa, from the Democratic Republic of the Congo and central Tanzania south to eastern South Africa. North of this area, it is mainly seen on migration, but occasionally winters in North Africa and to the west and north of its core area in southeast Africa. Most of the South African population of about 2,000 birds occurs in KwaZulu-Natal and the former Transvaal Province, and numbers elsewhere in Africa are uncertain. There are several nineteenth-century records, when populations were much higher than now, of birds being seen in western Europe, mainly Britain and Ireland, between December and February.<p>This crake migrates to Africa along two main routes: a western route through Morocco and Algeria, and a more important flyway through Egypt. On passage, it has been recorded in most countries between its breeding and wintering ranges, including much of West Africa. Birds from Coll following the western route paused in West Africa on their way further south, and again on the return flight, when they also rested in Spain or North Africa. Eastern migrants have been recorded in those parts of southern Asia that lie between the east of the breeding range and Africa. Further afield, the corn crake has been recorded as a vagrant to Sri Lanka, Vietnam and Australia, New Zealand, the Seychelles, Bermuda, Canada, the US, Greenland, Iceland, the Faroes, the Azores, Madeira, and the Canary Islands.<p>The corn crake is mainly a lowland species, but breeds up to 1,400 m (4,600 ft) altitude in the Alps, 2,700 m (8,900 ft) in China and 3,000 m (9,800 ft) in Russia. When breeding in Eurasia, the corn crake's habitats would originally have included river meadows with tall grass and meadow plants including sedges and irises. It is now mainly found in cool moist grassland used for the production of hay, particularly moist traditional farmland with limited cutting or fertiliser use. It also utilises other treeless grasslands in mountains or taiga, on coasts, or where created by fire. Moister areas like wetland edges may be used, but very wet habitats are avoided, as are open areas and those with vegetation more than 50 cm (20 in) tall, or too dense to walk through. The odd bush or hedge may be used as a calling post. Grassland which is not mown or grazed becomes too matted to be suitable for nesting, but locally-grown crops such as cereals, peas, rape, clover or potatoes may be used. After breeding, adults move to taller vegetation such as common reed, iris, or nettles to moult, returning to the hay and silage meadows for the second brood. In China, flax is also used for nest sites. Although males often sing in intensively managed grass or cereal crops, successful breeding is uncommon, and nests in the field margins or nearby fallow ground are more likely to succeed.<p>When wintering in Africa, the corn crake occupies dry grassland and savanna habitats, occurring in vegetation 30–200 cm (0.98–6.56 ft) tall, including seasonally burnt areas and occasionally sedges or reed beds. It is also found on fallow and abandoned fields, uncut grass on airfields, and the edges of crops. It occurs at up to at least 1,750 m (5,740 ft) altitude in South Africa. Each bird stays within a fairly small area. Although it sometimes occurs with the African crake, that species normally prefers moister and shorter grassland habitats than does the corn crake. On migration, the corn crake may also occur in wheatfields and around golf courses.

繁殖区

PAL : Europe to c Siberia and nw China

非繁殖区

s AF

迁徙

Complete migrants

行为

Migration pattern: Complete migrants.

保护状况

Population trend: stable.

种群趋势

stable