Species of bird
 ;templatestyles src="Template:Taxobox/core/styles.css" / ;
The water rail (Rallus aquaticus) is a bird of the rail family which breeds in well-vegetated wetlands across Europe, Asia and North Africa. Northern and eastern populations are migratory, but this species is a permanent resident in the warmer parts of its breeding range. The adult is long, and, like other rails, has a body that is flattened laterally, allowing it easier passage through the reed beds it inhabits. It has mainly brown upperparts and blue-grey underparts, black barring on the flanks, long toes, a short tail and a long reddish bill. Immature birds are generally similar in appearance to the adults, but the blue-grey in the plumage is replaced by buff. The downy chicks are black, as with all rails. The former subspecies "R. indicus", has distinctive markings and a call that is very different from the pig-like squeal of the western races, and is now usually split as a separate species, the brown-cheeked rail.
The water rail breeds in reed beds and other marshy sites with tall, dense vegetation, building its nest a little above the water level from whatever plants are available nearby. The off-white, blotched eggs are incubated mainly by the female, and the precocial downy chicks hatch in 19–22 days. The female will defend her eggs and brood against intruders, or move them to another location if they are discovered. This species can breed after its first year, and it normally raises two clutches in each season. Water rails are omnivorous, feeding mainly on invertebrates during summer and berries or plant stems towards winter. They are territorial even after breeding, and will aggressively defend feeding areas in winter.
These rails are vulnerable to flooding or freezing conditions, loss of habitat and predation by mammals and large birds. The introduced American mink has exterminated some island populations, but overall the species' huge range and large numbers mean that it is not considered to be threatened.
Taxonomy.
The rails are a bird family comprising around 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. However, the genus "Rallus", the group of long-billed reed bed specialists to which the water rail belongs, arose in the New World. Its Old World members, the water, African and Madagascar rails, form a superspecies, and are thought to have evolved from a single invasion from across the Atlantic. Genetic evidence suggests that the water rail is the most closely related of its genus to the Pacific "Gallirallus" rails, and is basal to that group. The water rail was first described by Carl Linnaeus in his 1758 10th edition of "Systema Naturae" under its current scientific name, "Rallus aquaticus". The binomial name is the Latin equivalent of the English "water rail" that had been used by English ornithologists Francis Willughby in 1676 and by Eleazar Albin in 1731.
The former subspecies "R. a. indicus" has very different vocalisations from the water rail, and it was considered to be a separate species in early works. It was restored as a full species "R. indicus", by Pamela Rasmussen in her "Birds of South Asia" (2005). Her treatment has gained acceptance, and is followed in "Birds of Malaysia and Singapore" (2010). A 2010 study of molecular phylogeny further supported the possibility of specific status for "R. indicus", which is estimated to have diverged from the Western forms around 534,000 years ago.
Fossils.
The oldest known fossils of an ancestral water rail are bones from Carpathia dated to the Pliocene (1.8-5.3 million years ago). By the late Pleistocene, two million years ago, the fossil evidence suggests that the water rail was present across most of its present range. This species is well-recorded, with over 30 records from Bulgaria alone, and many others from across southern Europe. and China. A rail from Eivissa, "Rallus eivissensis", was smaller but more robust than the water rail, and probably had poorer flight abilities. In the Quaternary, the island lacked terrestrial mammals, and this distinctive form presumably descended from its continental relative. It became extinct at about the same time as human arrival on the island, between 16,700 and 5,300 BC. The nominate race of water rail is now a very rare resident on Eivissa.
Description.
The adult of the nominate subspecies is a medium-sized rail, long with a wingspan. Males typically weigh and females are slightly lighter at . The upper parts from the forehead to tail are olive-brown with black streaks, especially on the shoulders. The sides of the head and the underparts down to the upper belly are dark slate-blue, except for a blackish area between bill and eye, and brownish sides to the upper breast. The flanks are barred black and white, and the undertail is white with some darker streaks. The long bill and the iris are red, and the legs are flesh-brown. The sexes are similar; although the female averages slightly smaller than the male, with a more slender bill, determining sex through measurements alone is unreliable. The juvenile has a blackish crown and a white chin and throat. The underparts are buff or white with darker bars, and the flank markings are brown and buff, rather than black and white. The undertail is buff, and the eye, bill and leg colours are duller than the adult. The downy chick is all black apart from a mainly white bill. After breeding, the rail has an extensive moult, and is flightless for about three weeks. Individual adults can be identified by the markings on the undertail, which are unique to each bird. Adult males have the strongest black undertail streaks. It has been suggested that the dark barring on the undertail of this species is a compromise between the signalling function of a pure white undertail, as found in open water or gregarious species like the common moorhen, and the need to avoid being too conspicuous.
The water rail can readily be distinguished from most other reed bed rails by its white undertail and red bill; the latter is a little longer than the rest of the rail's head (55–58% of the total) and slightly down-curved. The somewhat similar slaty-breasted rail of tropical Asia has a stouter bill, a chestnut crown and white-spotted upperparts. Juvenile and freshly moulted water rails may show a buff undertail like spotted crake, but that species' plumage is spotted with white, and it has a much shorter, mainly yellowish bill. The range of the water rail does not overlap with that of any other "Rallus" species, but vagrants could be distinguished from their American relatives by the lack of rufous or chestnut on the closed wing. The larger African rail has unstreaked darker brown upperparts and brighter red legs and feet.
Vocalisations.
The water rail is a vocal species which gives its main call, known as "sharming", throughout the year. This is a series of grunts followed by a high-pitched piglet-like squeal and ending in more grunts. It is used as a territorial call, alarm and announcement. Members of a pair may call alternately, the male giving lower and slower notes than his partner. The courtship song, given by both sexes, is a "tyick-tyick-tyick" often ending with a trill from the female; the male may sing for hours. The flight call is a sharp whistle, and other vocalizations include a loud repeated creak given by the male when showing the nest site to the female, and a purring given by both parents when at the nest with chicks. The rails are most vocal when setting up a territory and early in the breeding season, when calling may continue at night. Chicks initially cheep weakly, but soon develop a "tyk-tyk-trik" begging call.
When researchers played recordings of the reed warbler at night to attract that species for trapping, they found water rails and other wetland birds were also grounded, despite a lack of suitable habitat, suggesting that the rails and other nocturnal migrants recognised the warbler's song and associated it with the marshy habitat in which it is usually found.
Subspecies.
There are three recognised subspecies.
The differences between the three other races appear to be clinal, and it is possible that they should all be merged into "R. a. aquaticus".
Distribution and habitat.
The water rail breeds across temperate Eurasia from Iceland and Ireland discontinuously to North Africa, Saudi Arabia and western China. Its distribution in Asia is poorly studied.
The Icelandic population of water rail, "R. a. hibernans", became extinct around 1965, as a result of loss of habitat through the draining of wetlands, and predation by the introduced American mink.
Prior to its extinction, at least some birds were present year-round on the island, relying on warm volcanic springs to survive through the coldest months, but this race was also found in winter in the Faroe Islands and Ireland, and on passage through the Western Isles, suggesting that the Icelandic form was a partial migrant. The nominate subspecies, "R. a. aquaticus" is resident in the milder south and west of its range, but migrates south from areas that are subject to harsh winters. It winters within its breeding range, and also further south in North Africa, the Middle East and the Caspian Sea area. The peak migration period is September to October, with most birds returning to the breeding grounds from March to mid-April. A specimen of the nominate population labelled as "Baluchistan" and collected by Richard Meinertzhagen is considered of doubtful provenance. "R. a. korejewi" is another partial migrant, with some of the population wintering from Iraq and eastern Saudi Arabia eastwards through Pakistan and northern India to western China.
The breeding habitat of the water rail is permanent wetland with still or slow-moving fresh or brackish water and dense, tall vegetation, which may include common reed, reedmace, irises, bur-reed or sedges. In coastal areas, sea rush is common in saltmarsh breeding sites, with sedges and bur-reed dominant in somewhat less saline environments. A study in the Netherlands and Spain showed that the rush provided better concealment than the other maritime plants. As elsewhere, nests were constructed from the nearest available plants. Where it occurs, saw-sedge provides good breeding habitat, its tall () dense structure providing good cover for the nesting rails. The preferred habitat is "Phragmites" reedbed with the plants standing in water, with a depth of , muddy areas for feeding and a rich diversity of invertebrate species. Locations with nearby willows or shrubs are favoured above large areas of uniform habitat. In addition to natural fresh or marine marshes, this rail may use gravel or clay excavations and peat workings as long as there is suitable habitat with good cover. It may be found in rice paddies or on floating islands, and it occurs in Kashmir in flooded sugarcane fields. A Finnish study showed that the main factor influencing the distribution of water rails was the extent of vegetation cover, with the highest densities in the most vegetated areas; the presence of other marshes nearby was also significant. However, factors such as temperature, rainfall, length of shore line and extent of peat, important for some other marsh birds, were not statistically relevant. The areas with the highest densities of the rail also had the greatest numbers of three species considered at risk in Finland, the great reed warbler, Eurasian bittern and marsh harrier. The northern limit of breeding seems to be determined by the transition from nutrient-rich wetland to poorer, more acidic water. This leads to the replacement of common reed by a more open vegetation type dominated by marsh cinquefoil, which is unsuitable for the rails.
Occasionally, more unusual locations are used. One pair in Scotland nested in the open by the side of a road, and when an English nature reserve installed nest boxes for bearded tits (reed "wigwams" with a wooden floor), rails nested both in the boxes and under the wooden floor, in the latter case sometimes with the tits in residence above. Although mainly a lowland species, the water rail breeds at in the Alps and in Armenia. An Italian study suggested that reed bed birds need a minimum area of wetland for breeding, which for the water rail is about , although the highest densities are in marshes of or more.
On migration and in winter, a wider range of wet habitats may be used, including