Rails (avian familyRallidae) are a large,cosmopolitanfamily of small- to medium-sized terrestrial and/or semi-amphibiousbirds. The family exhibits considerable diversity in its forms, and includes such ubiquitous species as the crakes,coots, andgallinule; other rail species are extremely rare or endangered. Many are associated withwetland habitats, some being semi-aquatic likewaterfowl (such as the coot), but many more are wading birds or shorebirds. The ideal rail habitats aremarsh areas, includingrice paddies, and flooded fields or open forest. They are especially fond of dense vegetation for nesting.[2] The rail family is found in everyterrestrialhabitat with the exception of drydesert,polar or freezing regions, andalpine areas (above thesnow line). Members of Rallidae occur on every continent exceptAntarctica. Numerous unique island species are known.
"Rail" is the anglicized respelling of the Frenchrâle, fromOld Frenchrasle. It is named from its harsh cry, inVulgar Latin *rascula, fromLatinrādere ("to scrape").[3]
South Islandtakahē (Porphyrio hochstetteri) from behind, showing the short, soft, and fluffyremiges typical of flightless rails
The rails are a family of small to medium-sized, ground-living birds. They vary in length from 12 to 63 cm (5 to 25 in) and in weight from 20 to 3,000 g (0.7 oz to 6 lb 10 oz). Some species have long necks and in many cases are laterally compressed.[4]
Thebill is the most variable feature within the family. In some species, it is longer than the head (like theclapper rail ofthe Americas); in others, it may be short and wide (as in thecoots), or massive (as in thepurple gallinules).[5] A few coots and gallinules have afrontal shield, which is a fleshy, rearward extension of the upper bill. The most complex frontal shield is found in thehorned coot.[6]
The wings of all rails are short and rounded. Theflight of those Rallidae able to fly, while not powerful, can be sustained for long periods of time, and many speciesmigrate annually. The weakness of their flight, however, means they are easily blown off course, thus making them commonvagrants, a characteristic that has led them to colonize many isolated oceanic islands. Furthermore, these birds often prefer to run rather than fly, especially in dense habitat. Some are also flightless at some time during theirmoult periods.[8]
Flightlessness in rails is one of the best examples ofparallel evolution in the animal kingdom. Of the roughly 150 historically known rail species, 31 extant or recently extinct species evolved flightlessness from volant (flying) ancestors.[9] This process created the endemic populations of flightless rails seen on Pacific islands today.
Many island rails are flightless because small island habitats without mammalian predators eliminate the need to fly or move long distances.Flight makes intense demands, with thekeel and flight muscles taking up to 40% of a bird's weight.[9] Reducing the flight muscles, with a corresponding lowering ofmetabolic demands, reduces the flightless rail's energy expenditures.[10] For this reason, flightlessness makes it easier to survive and colonize an island where resources may be limited.[11] This also allows for the evolution of multiple sizes of flightless rails on the same island as the birds diversify to fill niches.[12]
In addition to energy conservation, certain morphological traits also affect rail evolution. Rails have relatively small flight muscles and wings to begin with.[13] In rails, the flight muscles make up only 12–17% of their overall body mass.[9] This, in combination with their terrestrial habits and behavioral flightlessness, is a significant contributor to the rail's remarkably fast loss of flight;[14] as few as 125,000 years were needed for theLaysan rail to lose the power of flight and evolve the reduced, stubby wings only useful to keep balance when running quickly.[15] Indeed, some argue that measuring the evolution of flightlessness in rails in generations rather than millennia might be possible.[11]
Another factor that contributes to the occurrence of the flightless state is a climate that does not necessitate seasonal long-distance migration; this is evidenced by the tendency to evolve flightlessness at a much greater occurrence in tropical islands than in temperate or polar islands.[16]
It is paradoxical, since rails appear loath to fly, that the evolution of flightless rails would necessitate high dispersal to isolated islands.[13] Nonetheless, three species of small-massed rails,Gallirallus philippensis,Porphyrio porphyrio, andPorzana tabuensis, exhibit a persistently high ability to disperse long distances among tropic Pacific islands,[13] though only the latter two gave rise to flightless endemic species throughout the Pacific Basin.[17] In examining the phylogeny ofG. philippensis, although the species is clearly polyphyletic (it has more than one ancestral species), it is not the ancestor of most of its flightless descendants, revealing that the flightless condition evolved in rails before speciation was complete.[17]
A consequence of lowered energy expenditure in flightless island rails has also been associated with evolution of their "tolerance" and "approachability".[16] For example, the (non-Rallidae) Corsicanblue tits exhibit lower aggression and reduced territorial defense behaviors than do their mainland European counterparts,[18] but this tolerance may be limited to close relatives.[19] The resulting kin-selecting altruistic phenomena reallocate resources to produce fewer young that are more competitive and would benefit the population as an entirety, rather than many young that would exhibit less fitness.[16] Unfortunately, with the human occupation of most islands in the past 5,000 to 35,000 years, selection has undoubtedly reversed the tolerance into a wariness of humans and predators, causing species unequipped for the change to become susceptible to extinction.[16]
In general, members of the Rallidae are omnivorous generalists. Many species eatinvertebrates, as well as fruit or seedlings. A few species are primarilyherbivorous.[2] Thecalls of Rallidae species vary and are often quite loud. Some are whistle-like or squeak-like, while others seem unbirdlike.[20] Loud calls are useful in dense vegetation, or at night where seeing another member of the species is difficult. Some calls areterritorial.[5]
The most typical family members occupy densevegetation in damp environments nearlakes,swamps, orrivers.Reed beds are a particularly favoured habitat. Those thatmigrate do so at night.
Mostnest in dense vegetation. In general, they are shy, secretive, and difficult to observe. Most species walk and run vigorously on strong legs, and have long toes that are well adapted to soft, uneven surfaces. They tend to have short, rounded wings, and although they are generally weakfliers, they are, nevertheless, capable of covering long distances. Island species often becomeflightless, and many of them are nowextinct following the introduction of terrestrialpredators such ascats,foxes,weasels,mongooses,rats, andpigs.
Manyreedbed species are secretive (apart from loud calls),crepuscular, and have laterally flattened bodies. In theOld World, long-billed species tend to be called rails and short-billed species crakes.North American species are normally called rails irrespective of bill length. The smallest of these isSwinhoe's rail, at 13 cm (5.1 in) and 25 g. The larger species are also sometimes given other names. The black coots are more adapted to open water than their relatives, and some other large species are called gallinules and swamphens. The largest of this group is thetakahē, at 65 cm (26 in) and 2.7 kg (6.0 lb).
The rails have suffered disproportionally from human changes to the environment, and an estimated[21][22][23] several hundred species of island rails have become extinct because of this. Several island species of rails remainendangered, andconservation organisations and governments continue to work to prevent their extinction.
The breeding behaviors of many Rallidae species are poorly understood or unknown. Most are thought to bemonogamous, althoughpolygyny andpolyandry have been reported.[24] Most often, they lay five to 10eggs.Clutches as small as one or as large as 15 eggs are known.[24] Egg clutches may not always hatch at the same time. Chicks become mobile after a few days. They often depend on their parents until fledging, which happens around 1 month old.[6]
Due to their tendencies towards flightlessness, many island species have been unable to cope with introduced species. The most dramatic human-caused extinctions occurred in thePacific Ocean as people colonised the islands ofMelanesia,Polynesia, andMicronesia, during which an estimated 750–1800 species of birds became extinct, half of which were rails.[27] Some species that came close to extinction, such as theLord Howe woodhen, and the takahē, have made modest recoveries due to the efforts of conservation organisations. TheGuam rail came perilously close to extinction whenbrown tree snakes were introduced toGuam, but some of the last remaining individuals were taken into captivity and are breeding well, though attempts at reintroduction have met with mixed results.[28][29][30]
The family Rallidae was introduced (as Rallia) by the FrenchpolymathConstantine Samuel Rafinesque in 1815.[31][32]The family has traditionally been grouped with two families of larger birds, thecranes andbustards, as well as several smaller families of usually "primitive" midsized amphibious birds, to make up the orderGruiformes. The alternativeSibley-Ahlquist taxonomy, which has been widely accepted in America, raises the family to ordinal level as the Ralliformes. Given uncertainty about gruiformmonophyly, this may or may not be correct; it certainly seems more justified than most of the Sibley-Ahlquist proposals. However, such a group would probably also include theHeliornithidae (finfoots and sungrebes), an exclusivelytropical group that is somewhatconvergent withgrebes, and usually united with the rails in the Ralli.
Thecladogram below showing the phylogeny of the living and recently extinct Rallidae is mostly based on a study by Juan Garcia-R and collaborators published in 2020.[7] The position of thechestnut-headed crake (Anurolimnas castaneiceps) and the arrangement in the tribe Laterallini is based on the study by Emiliano Depino and collaborators that was published in 2023.[33] The genera and number of species are taken from the list maintained byFrank Gill,Pamela Rasmussen and David Donsker on behalf of theInternational Ornithological Committee (IOC).[34] The names of the subfamilies and tribes are those proposed by Jeremy Kirchman and collaborators in 2021.[1]
Additionally, many prehistoric rails of extant genera are known only fromfossil or subfossil remains, such as theIbiza rail (Rallus eivissensis). These have not been listed here; see the genus accounts and the articles onfossil andLate Quaternary prehistoric birds for these species.
Mundia –Ascension crake (recently extinct; flightless, single island, lost by early 1800s to introduced cats and rats)
Aphanocrex –Saint Helena rail (recently extinct; flightless, single island, lost by 1500s to introduced cats and rats)
Diaphorapteryx –Hawkins's rail (recently extinct; flightless, two islands, lost between 1500 and 1700 to overhunting)
Aphanapteryx –Red rail (recently extinct; flightless, single island, lost by 1700 to overhunting and introduced pigs, cats and rats)
Erythromachus –Rodrigues rail (recently extinct; flightless, single island, lost by 1760 to overhunting, destruction of habitat by tortoise hunters, and introduced cats)
The undescribed Fernando de Noronha rail, genus and species undetermined, survived to historic times. The extinct genusNesotrochis from the Greater Antilles was formerly considered to be a rail, but based on DNA evidence is now known to be an independent lineage of gruiform more closely related toSarothruridae andadzebills.
GenusTelecrex (Irdin Manha Late Eocene of Chimney Butte, China)
GenusAmitabha (Bridger middle Eocene of Forbidden City, USA) – phasianid?
GenusPalaeocrex (Early Oligocene of Trigonias Quarry, USA)
GenusRupelrallus (Early Oligocene of Germany)
Neornithes incerta sedis (Late Oligocene of Riversleigh, Australia)[45]
GenusEuryonotus (Pleistocene of Argentina)
The presumed scolopacidwaderLimosa gypsorum (Montmartre Late Eocene of France) is sometimes considered a rail and then placed in the genusMontirallus.[46]
^Bock, Walter J. (1994).History and Nomenclature of Avian Family-Group Names. Bulletin of the American Museum of Natural History. Vol. 222. New York:American Museum of Natural History. pp. 136, 252.hdl:2246/830.
^Depino, E.A.; Pérez-Emán, J.L.; Bonaccorso, E.; Areta, J.I. (2023). "Evolutionary history of New World crakes (Aves: Rallidae) with emphasis on the tribe Laterallini".Zoologica Scripta.52 (4).doi:10.1111/zsc.12595.
^Several limb bones of a smallish rail: Gálet al. (1998–99)
^Partial hand of acommon moorhen-sized rail: Ballmann (1969)
^Olson, Storrs L. (1974). "A new species of Nesotrochis from Hispaniola, with notes on other fossil rails from the West Indies (Aves: Rallidae)".Proceedings of the Biological Society of Washington.87(38): 439–450.hdl:10088/8374.
^SpecimenQM F40203. A leftcarpometacarpus piece of a bird about the size ofLewin's rail. Probably from a rail, but it is too damaged to determine its affiliations more precisely:Boles [de] (2005)
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