Crex

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For other uses, see Crex (disambiguation).
Crex
upstretched head and neck of a greyish bird
Corn Crake
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Gruiformes
Family: Rallidae
Genus: Crex
Bechstein, 1803[1]
Species

Corn Crake, C. crex
African Crake, C. egregia

Synonyms

Ortygometra
Crecopsis

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[edit]

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.[1] 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.[2]

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,[3] and has variously been placed in the genus Porzana or its own genus, Crecopsis, but is now more usually placed in Crex.[4][5] 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.[6]

The genus name is onomatopoeic, referring to the repetitive grating call of the Corn Crake.[7] 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.[8]

Description[edit]

brown bird with grey head, striped flanks and red legs, facing left
African Crake

Both Crex crakes are short-billed birds with blackish-brown upperparts and mainly blue-grey underparts. The belly is white, and there is barring on the flanks and the underside of the short tail. The Corn Crake is significantly larger than its relative, at 27–30 cm (10.6–11.8 in) long with a wingspan of 42–53 cm (16.5–20.9 in), compared to the African Crake's 20–23 cm (7.8–9.1 in) length and a 40–42 cm (15.7–16.5 in) wingspan. The Corn Crake is sympatric with the African Crake on its wintering grounds, but can be distinguished by its larger size, paler upperparts, chestnut-coloured patch on the 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.[9][10]

The sexes of each species are similar in appearance, although the females are slightly smaller and duller than the males, with a less contrasting head pattern. Juveniles of both species are duller than the adults, and browner underneath. Adults undergo a complete moult after breeding. No subspecies have been recognised of either Crex crake. Although Corn Crakes become paler and greyer towards the east of the range, the change is clinal, and there is great individual variation in colour within all populations.[9][10]

The two Crex crakes are unlikely to be confused with other rails, since most sympatric short-billed rails are smaller, with white markings on the upperparts, different underparts patterns and shorter bills. The European Water Rail and the African Rail have long pointed bills.[9][10]

Voice[edit]

Like other rails, the Crex species have a wide range of vocalisations. The males of both crakes have a loud territorial and advertising call consisting of a series of grating notes repeated two or three times a second for several minutes. The male stands upright with his neck extended when advertising, with its head and neck almost vertical and bill wide open. Calling is most frequent early in the breeding season, mainly at night for the Corn Crake, but in the day for its African cousin.[9][10] The Corn Crake's call may be repeated more than 20,000 times a night, with a peak between midnight and 3 am.[11]

Male Corn Crake advertising call

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The advertising calls of both crakes are readily distinguished from the quite dissimilar calls of potentially sympatric rails such as the Spotted Crake, Striped Crake, Baillon's Crake,[12] or Water Rail.[13] The calls of the two Crex species cannot be confused, since the Corn Crake is silent in Africa.[14] Both sexes may give distinctive territorial or alarm calls, and females and chicks communicate with cheeps and wheezes. The African Crake can be attracted to within 10 m (30 ft) of a human by imitation of its kraaa threat call,[9] and the male Corn Crake by mechanical imitations of their advertising call, including rubbing a piece of wood down a notched stick, or by flicking a credit card against a comb or zip-fastener.[11]

Distribution and habitat[edit]

alt
alt
Approximate ranges of Corn Crake (left) and African Crake (right)
       Breeding summer visitor
       Resident year-round
       Winter visitor

The Corn Crake is a long distance migrant, breeding across temperate Eurasia from the British Isles east to central Siberia and western China.[15][16] It winters in Africa from Zaire and central Tanzania south to eastern South Africa, mainly KwaZulu-Natal and the former Transvaal Province.[10] Small numbers of birds may winter in the milder areas of western Europe, or halt their migration and stay in North Africa.[17]

The African Crake occurs throughout sub-Saharan Africa from Senegal east to Kenya and south to KwaZulu-Natal, except in arid areas of south and southwest Africa where the annual summer rainfall is less than 300 mm (11.8 in). It is widespread and locally common in most of its range, apart from the rainforests and the drier regions. Nearly all the South African population of about 8,000 birds occur in KwaZulu-Natal and the former Transvaal Province. This crake is only a vagrant to the drier zones on the southern edges of South Africa's northern and eastern Cape Province and North West Province,[9][18] and southern Botswana.[19]

Both species are nocturnal migrants. Most Corn Crakes migrate through Egypt, with smaller numbers crossing at the western end of the Mediterranean. It has been recorded in most countries between its breeding and wintering ranges, including much of west Africa,[10] and those parts of southern Asia that lie between the east of the breeding range and Africa. Further afield, it has been recorded as a vagrant to Sri Lanka, Vietnam and Australia,[16] the Seychelles,[20] Bermuda,[21] Canada, the United States, Greenland,[10] and the North Atlantic islands.[17]

The African species is a partial migrant, but its movements are complex, seasonal and poorly studied. It is mainly a wet-season breeder, and many birds move away from the equator as soon as the rains provide sufficient grass cover to allow them to breed elsewhere. Southward movement is mainly from November to April, the return north beginning when burning or drought reduces the grass cover again. This species is present throughout the year in some West African countries, and in equatorial regions, but even in those areas numbers vary seasonally due to local movements; internal north–south migration has been noted within countries including Nigeria, Senegal, The Gambia, Côte d'Ivoire and Cameroon.[9] This crake has also wandered further afield. It is rare on Bioko Island (Equatorial Guinea),[22] and there have been two records each for São Tomé and Tenerife, the Canary Islands birds being the first records for the Western Palaeartic.[23][24]

tall grass with trees in the distance
Grasslands in Africa are the main year-round location for African Crake, and form the wintering habitat for Corn Crake.

Most rails are wetland birds, but the two Crex species prefer drier habitats. The African Crake is found mainly in grassland, ranging from wetland edges and seasonal floodlands to savanna, lightly wooded dry grassland, and grassy forest clearings. It also frequents maize, rice and cotton crops, derelict farmland and sugarcane plantations close to water. A wide range of grass species are used, with a preferred height of 0.3–1 m (1–3 ft) tall but vegetation is acceptable up to 2 m (6 ft) tall. 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 (8,600 ft) in China and 3,000 m (9,800 ft) in Russia.[16][17] When breeding in Eurasia, the Corn Crake's habitats would originally have included river meadows with tall grass and meadow plants, but it is now mainly found in cool moist grassland used for the production of hay, particularly moist traditional farmland. It also utilises other treeless grasslands in mountains or taiga, on coasts, or where created by fire. Very wet habitats are avoided, as are open areas and those with vegetation more than 50 cm (20 in) tall, or too dense for the birds to walk through.[10]

While wintering in Africa, the Corn Crake occupies dry grassland and savanna habitats, occurring in vegetation 30–200 cm (1–6 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 (5,700 ft) altitude in South Africa.[10] Although it sometimes occurs with the African Crake, that species normally prefers moister and shorter grassland habitats than does the Corn Crake.[9] On migration, the Corn Crake may also occur in wheatfields and around golf courses.[10]

Behaviour[edit]

Both Crex crakes are mainly active during the day, especially at dawn, dusk, during light rain, or after heavier rain. The African Crake is less skulking and easier to flush from cover than other crakes, and is often seen at the edges of roads and tracks, but the Corn Crake is a much more difficult bird to see in its breeding sites, usually being hidden by vegetation and rarely emerging into the open. Both crakes are territorial on both the breeding and non-breeding grounds; the male threat displays involves the bird standing upright and spreading the feathers of the wings, flanks and belly like a fan. Fighting at territorial boundaries involves the male birds jumping at each other and pecking.[9][10]

Both species walk with a high-stepping action, and can run swiftly through grass with the body held horizontal and laterally flattened. When disturbed, they typically fly less than 50 m (150 ft), frequently landing behind a bush or thicket, and then go into a crouch. In short grass, they can escape from a dog using their speed and maneuverability, running with the body held almost horizontal. The typical flight is weak and fluttering, especially that of the African Crake, but for longer flights, such as migration, the Corn Crake has a steadier, stronger action with its legs drawn up. Flocks of up to 40 Corn Crakes may form on migration, sometimes associating with Common Quails. Migration takes place at night, and flocks resting during the day may aggregate to hundreds of birds at favoured sites.[9][10] The ability to migrate is innate, not learned from adults; chicks raised from birds kept in captivity for ten generations were able to migrate to Africa and return with similar success to wild-bred young.[25]

Breeding[edit]

cream-coloured egg with red-brown blotches
Illustration of a Corn Crake egg

Both crakes were formerly believed to be monogamous, but the male Corn Crake may have a shifting home range, and mate with two or more females, moving on when laying is almost complete. The breeding display consists of a short chase of the female by the male. The nest is a shallow cup of grass leaves and lined with finer grasses, built in a depression and well hidden in the grass. The clutch size is from 3 to 11 pink eggs for the African species,[26] and 6–14 – usually 8–12 – for the European breeder. The Corn Crake's eggs are oval, slightly glossy, creamy or tinted with green, blue or grey, and blotched red-brown. They average 37 × 26 mm, (1.5 × 1.0 in) and weigh about 13–16 g, (0.46–0.56 oz),[10] of which 7% is shell.[27]

The first egg is often laid when the nest is little more than a pad of grass, and a further egg is laid on each subsequent day. Both sexes incubate the eggs, which start hatching after about 14 days; all hatch with 48 hours despite the extended laying period. The black, downy precocial chicks soon leave the nest but are fed and protected by the parents. Fledging occurs after four to six weeks, and the young can fly before they are fully grown. It is not known whether the African Crake has a second brood, but the Corn Crake usually does. Where grass is not tall enough at the start of the season, the first nest may be constructed in herby or marsh vegetation, with the second brood in hay.[10] The second nest may also be at a higher altitude that the first, to take advantage of the later-developing grasses further up a hill.[28][29]

Although survival in undisturbed sites is high, at 80–90%, the Corn Crake suffers from modern farming practices, since mechanised mowing can kill 38–95% of chicks in a given site.[10] The influence of weather on Corn Crake chick survival is limited: although chick growth is faster in dry or warm weather, the effects are relatively small. Unlike many precocial species, chicks are fed by their mother for a few days until they become independent, and this may cushion them from adverse conditions. The number of live chicks hatched is more important than the weather, with lower survival in large broods.[30]

Feeding[edit]

Both Crex crakes are omnivorous, but mainly feed on invertebrates, including earthworms, slugs and snails, spiders, beetles, dragonflies, grasshoppers and other insects. The Corn Crake may take pests such as Sitona weevils, leatherjackets and wireworms. In Africa, termites, cockroaches and dung beetles may be consumed. These opportunist hunters will take the occasional vertebrate such as a small frog, rodent or fish. Food is taken from the ground, low-growing plants and from inside grass tussocks; the crake may search leaf litter with its bill, and run in pursuit of active prey. In Africa, both species will occasionally feed on grassy tracks or dirt roads. Plant material is eaten, especially grass seeds, but also green shoots, leaves and other seeds. As with other rails, grit is swallowed to help break up food in the stomach. Indigestible material is regurgitated as pellets. Chicks are fed mainly on animal food. Crex crakes forage singly, in pairs or in family groups, sometimes in association with the other member of the genus or with other grassland birds such as Great Snipes, Blue Quails and Common Quails.[9][10]

Predators and parasites[edit]

Predators of the Corn Crake on its European breeding grounds include feral and domestic cats, introduced American Mink, feral Ferrets, Otters and Red Foxes, and birds including the Common Buzzard and Hooded Crow.[10] In Lithuania, the introduced Raccoon Dog has also been recorded taking Corn Crakes. When chicks are exposed by rapid mowing, they may be taken by large birds including the White Stork, harriers and other birds of prey, gulls and corvids.[31] At undisturbed sites, nests and broods are rarely attacked, which is reflected in the high breeding success.

In Africa, Crex species may be hunted by the Leopard,[32] Serval, cats, the Black-headed Heron, Dark Chanting Goshawk, African Hawk-Eagle, Wahlberg's Eagle,[9] and Black Sparrowhawk.[10] In South Africa, newly hatched African Crake chicks were taken by a Boomslang.[33]

Parasites recorded in this genus include the widespread fluke Prosthogonimus ovatus( which lives in the oviducts of birds),[34] the parasitic worm Plagiorchis elegans,[35] the larvae of parasitic flies,[36] the feather mite Metanalges elongatus,[37] and hard ticks of the genera Haemaphysalis and Ixodes.[38][39][40] During the reintroduction of Corn Crakes to England in the 2003 breeding season, enteritis and ill heath in pre-release birds was due to bacteria of a pathogenic Campylobacter species. Subsequently, microbiology tests were done to detect infected individuals and to find the source of the bacteria in their environment.[41]

Status[edit]

Both Crex species have huge breeding ranges, estimated at 15,700,000 km2 (4,500,000 mi2) for the African Crake and 12,400,000 km2 (4,800,000 mi2) for the Corn Crake. The population size of the African species is unknown, but it is common in most of its range, and its numbers appear to be stable. The European bird has an estimated 1.3–2.0 million breeding pairs in Europe, three-quarters of which are in European Russia, and a further 515,000–1,240,000 pairs in Asiatic Russia; the total Eurasian population has been estimated at between 5.45 and 9.72 million individuals. Both species are classed as Least Concern on the IUCN Red List. The Corn Crake was formerly classified as Near Threatened because of serious declines in Europe, but improved monitoring in Russia indicates that anticipated losses there have not occurred and numbers have remained stable or possibly increased in Russia and Kazakhstan.[28][42] Although most rails in the Old World are covered by the Agreement on the Conservation of African-Eurasian Migratory Waterbirds (AEWA), neither Crex species is listed, being too terrestrial to be classed as wetland species.[43]

Overgrazing, agriculture and the loss of wetland and moist grassland have reduced the availability of suitable habitat for the African Crake in many areas, such as some parts of the southern KwaZulu-Natal coast which have been urbanised or planted with sugarcane. In other areas, grassland may have increased locally in recent years as woodland is cleared. This crake is considered to be good eating, and is killed for food in some regions. Despite these adverse factors, it appears to be under no real threat.[9]

In much of the western half of the Corn Crake's breeding range, there have been long-term declines that are expected to continue, although conservation measures have enabled numbers to grow in several countries, including substantial increases in the small populations in Finland, the UK and the Netherlands.[44] The breeding population had begun to decline in the 19th century, but the process gained pace after World War II.[45] The main cause of the steep declines in much of Europe 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, at first horse-drawn and later pulled by tractors. Mechanisation also means that large areas can be cut quickly, leaving the crake with no alternative sites to raise either a first brood if suitable habitat has gone, or a replacement brood if the first nest is destroyed.[31] The pattern of mowing, typically in a circular pattern from the outside of a field to its centre, gives little chance of escape for the chicks, which are also exposed to potential animal predators. Adults can often escape the mowers, although some incubating females sit tight on the nest, with fatal results.[10]

old black-and-white photo of hay wagon
Traditional hay-making

Loss of habitat is the other major threat to the Corn Crake, since 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.[31] More localised threats include floods in spring,[46] and disturbance by roads or wind farms,[31] and the loss of many birds – up to 14,000 a year – in Egypt, where migrating birds are captured in nets set for the quail with which they often migrate.[11] Although this may account for 0.5–2.7% of the European population, the losses to this form of hunting are less than when the targeted species were more numerous and predictable.[47]

Most European countries have taken steps to conserve the Corn Crake and produce national management policies; there is also an overall European action plan. The focus of conservation effort is to monitor populations and ecology and to improve survival, principally through changing the timing and method of hay harvesting.[28] Later cutting gives time for breeding to be completed, and leaving uncut strips at the edges of fields and cutting from the centre outwards reduces the casualties from mowing.[10] Implementing these changes is predicted to stop the population decline if the measures are applied on a sufficiently large scale.[48] Reduction of illegal hunting, and protection in countries where hunting is still allowed, are also conservation aims.[28] Reintroduction of the Corn Crake is being attempted in England, and breeding sites are scheduled for protection in many other countries.[49] Where breeding sites impinge on urban areas, there are cost implications, estimated in one German study at several million euros per Corn Crake.[50] The Corn Crake does not appear to be seriously threatened on its wintering grounds and may benefit from deforestation, which creates more open habitats.[28]

References[edit]

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