| Zapornia | |
|---|---|
.jpg) | |
| Baillon's crake,Zapornia pusilla | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Aves |
| Order: | Gruiformes |
| Family: | Rallidae |
| Genus: | Zapornia Leach, 1816 |
| Type species | |
| Gallinula minuta[1] Montagu, 1813 | |
| Species | |
10 living, andsee text | |
| Synonyms | |
AphanolimnasSharpe, 1892 | |
Zapornia is a recently revalidatedgenus of birds in the rail familyRallidae; it was included inPorzana for much of the late 20th century.[2] These smallish to tiny rails are found across most of the world, but are entirely absent from the Americas except as wind-blown stray birds (which are regularly encountered on the Atlantic coasts however). A number of species, and probably an even larger number of prehistorically extinct ones, are known only from small Pacific islands; several of these lost the ability to fly in the absence of terrestrialpredators. They are somewhat less aquatic thanPorzana proper, inhabiting the edges of wetlands, reedbelts, but also drier grass- and shrubland and in some cases open forest.[3]
They are medium brown to blackish above, at least from the neck backwards but usually also on the top of the head, uniformly coloured or with some rather inconspicuous (unlike the boldly spottedPorzana proper) pattern of some blackish and/or whitish spots on the wings and back and/or a grey stripe above the eyes. The lower parts, from the bill to the legs, have grey plumage in most species - ranging from pale to almost black -, but are light ruddy-brown in a few. Between legs and tail, the plumage is brown to black, and in many species features more or less conspicuous whitish barring as in many other genera of rails (includingPorzana proper). Some species (in particular small-island ones) appear uniformly drab brown or blackish-grey, with little discernible pattern when not seen up close. The eyes are usually red to chestnut-brown; the bill is short and straight by rail standards, greenish-yellow in most species, but bright yellow or blackish in a few. The legs have a greenish to reddish colouration even in the otherwise quite uniformly dusky species, and in some species are bright red[3]
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The genusZapornia was introduced in 1816 by the English zoologistWilliam Elford Leach in a catalogue of animals in theBritish Museum. He included a single species, theLittle crake, which is therefore thetype species.[4] The genus name is a near-anagram of the French ornithologistLouis-Pierre Vieillot's genusPorzana.[5]
However, Leach's proposal was not widely adopted. During the 1840sZapornia was used as a "wastebin taxon" for newly-discovered small rails from all over the world, few of which actually belong to today'sZaporniaclade; in 1880, even theSlender-billed flufftail was placed here, which eventually turned out to be no rail (familyRallidae) at all, but rather an aberrant crake-like member of the flufftail familySarothruridae. Subsequently, Leach's genus was generally synonymized withPorzana, assuming that species such as the Little andBaillon's crake were merely diminutive representatives of that genus. From the late 19th to the mid-20th century, any newly-discoveredZapornia crakes were either assigned to new and usuallymonotypic genera, or – increasingly often – lumped with their presumed relatives inPorzana. In his 1973 review of rail systematics,Storrs Olson noted that the mutual delimitation of the (loosely-circumscribed)Porzana andAmaurornis was "[o]ne of the most difficult problems in rail taxonomy" and found no way to resolve it to his satisfaction. He concluded that the two genera werepolyphyletic with regard to each other, and recommended including the numerous small segregate genera of Pacific island crakes inPorphyria, and the African crakes sometimes separated asLimnocorax inAmaurornis, until a satisfying solution for the delimitation of the two larger genera could be proposed.[6]
The firstcladistic analyses, using morphological data, found it almost impossible to resolve anyphylogenetic structure inPorzana and similar genera, but indicated that the entire group was closely related toAmaurornis bush-hen and theLaterallus crakes, as well as tocoots (Fulica) andmoorhen (Gallinula).[3][7]Molecular phylogenetic studies starting in 2002[8] revealed thatPorzana proper was a well-distinct lineage which had abasal position among the entire aforementioned group, to which thesubfamily nameHimanthornithinae was applied as it also included the singularNkulengu rail of genusHimantornis, a highly aberranttropical rainforest species that was long considered to be the most "primitive" living rail. However, molecular data places not only the Nkulengu rail within the subfamily containingPorzana and its allies, but also the hugeswamphen (Porphyrio) which morphological analysis had resolved as another one of the most ancient extant lineages of rails (although Olson in 1973 had correctly allied them with the moorhen andPorphyrio). Unlike the other rail subfamily,Rallinae, which includes mostly mid-sized amphibious species, the Himanthornithinae unite both very large and very small rails, as well as decidedly aquatic and strongly terrestrial lineages; it is thus unsurprising that the morphological data could not resolve such anadaptive radiation to satisfaction.[2][3][9][10]
As for theZapornia crakes, they were found to be well distinct fromPorzana, leading to the reinstatement of the old genus. In addition, some species traditionally placed inAmaurornis were found to actually belong inZapornia, confirming Olson's 1973 suspicions. Surprisingly (except from abiogeographical perspective), the closest living relatives ofZapornia were found to be a group of South Asian crakes of genusRallina, whose range is essentially surrounded by that ofZapornia.Rallina crakes are adapted to a more terrestrial habitat and thus differ more strongly fromZapornia in anatomy than might be expected given their close relationship; also,Rallina as traditionally circumscribed included a number of species which – similar to theSlender-billed flufftail initially being placed inZapornia – actually belonged to the flufftail family and are nowadays separated as genusRallicula. The morphology ofRallina is thus stronglyconvergent with the unrelatedRallicula flufftails, as well as strongly divergent from its actual closest relatives inZapornia, causing studies which only utilize morphological data to fail recovering their true relationships.[2][7][10][11][12][13]
The genus contains the following extant species:[11][12]
| Image | Common name | Scientific name | Distribution |
|---|---|---|---|
_(53346732716).jpg) | Black crake | Zapornia flavirostra Formerly inAmaurornis,Limnocorax orPorzana | Sub-Saharan Africa |
_2.jpg) | Ruddy-breasted crake | Zapornia fusca Formerly inAmaurornis orPorzana | South, East, and Southeast Asia |
 | Band-bellied crake | Zapornia paykullii Formerly inAmaurornis orPorzana | Breeds in northeastern Asia, winters in Southeast Asia |
_(27830555559).jpg) | Brown crake | Zapornia akool Formerly inAmaurornis orPorzana | South Asia |
.jpg) | Little crake | Zapornia parva Formerly inPorzana | Breeds from Central Europe to western Asia, winters in northern Africa and Southwest Asia |
 | Baillon's crake | Zapornia pusilla Formerly inPorzana | Resident in southern and eastern Africa, Madagascar, parts of Indonesia, Australia, and New Zealand; also breeds across temperate Eurasia and winters in South and Southeast Asia to southern Japan |
 | Black-tailed crake | Zapornia bicolor Formerly inAmaurornis orPorzana | Northern inland of Southeast Asia |
| Sakalava rail | Zapornia olivieri Formerly inAmaurornis orPorzana | Western Madagascar | |
 | Spotless crake | Zapornia tabuensis Formerly inPorzana | Philippines, New Guinea and Australia, across southern Pacific Ocean to Marquesas Islands and New Zealand |
 | Henderson crake | Zapornia atra Formerly inNesophylax orPorzana | Henderson Island, southeastern Polynesia |
Due to the uncertain relationships of the extinct species (see below), the internalphylogeny ofZapornia is not well resolved. Severalclades can be distinguished with some certainty, however, and recognized assubgenera. Sometimes[14] they are even elevated to full genus level, but given the conflicting data about thebasal radiation ofZapornia, this remains conjectural for the time being. In particular the AfricanendemicsBlack crake andSakalava rail are the source of much uncertainty; they were considered closely related, even asuperspecies, and allied with theBlack-tailed crake when these three were still included inAmaurornis. This assumption was not based on quantitative analyses however, but on the similar appearance of Sakalava rail and Black-tailed crake and the fact that the Sakalava rail occurs on the western coast of Madagascar while the Black crake is found on the African mainland across theMozambique Channel. Altogether however, the Sakalava rail remains little-known, and consequently has rarely been included in modern studies.
The Black crake, meanwhile, was usually found in molecular phyogenetic analyses to be the most basal species ofZapornia as circumscribed here, but not always robustly so;[2][10][15] one early analysis of a limited amount ofmtDNA data,[8] however, robustly allied it with theBrown crake. There have been few analyses including all of Black, Black-tailed and Brown crakes as well as the Sakalava rail, and the situation is further confounded by the discovery that due to asequencing laboratory error the first published fullmitochondrial genome of the Brown crake (GenBank KJ192198/NC_023982) was actuallyCommon moorhen mtDNA, possibly with some contamination from theWhite-breasted waterhen,[16][17] causing unfounded doubts[18] about the Brown crake's inclusion inZapornia. The Black crake would constitute subgenusLimnocorax, but whether this is the basalmost branch of the livingZapornia (and thus the foremost candidate for splitting off the present genus) and/or includes the Brown crake requires further study.
The Ruddy-breasted and Band-bellied crakes, on the other hand, were never considered anything butsister species with almostparapatric distribution; this is supported by all molecular phylogenetic studies including those two species, but their placement with regard to the Black Rail lineage is uncertain;[2][8][15][19][20] Ruddy-breasted and Band-bellied crakes may also represent an ancient lineage ofZapornia – perhaps even older thanLimnocorax – and warrant recognition as subgenus (or even genus)Limnobaenus. Before the establishment ofLimnobaenus, the Ruddy-breasted crake (under itsjunior synonymRallus rubiginosus) had already been illustrated astype species of a genusCorethrura byGeorge Robert Gray in 1846; this name, confusingly, was at the same time considered byLudwig Reichenbach for the typicalflufftails but formally established for these only some years later, leading to itsinvalidity and eventual replacement by the current nameSarothrura. Further adding to the confusion, in the 1855 edition of his species catalogue, Gray subsumed hisCorethrura inRallina, with theRed-legged crake (R. fasciata) as type species.[21] However, even before Gray,Frederick William Hope had establishedCorethrura as a genus oflophopidplanthoppers, and thus Gray's name was invalid too.[22]
Likewise, a close relationship between the Little and Baillon's crakes has been suggested by most if not all authors from an early date onwards, and is well supported by the molecular data too. As this group contains the genus'type species, it would be subgenusZapornia, but as it contains at least some if not most of the extinct members of the genus, its circumscription is not fully resolved.[2][8][15][20] Much of this uncertainty derives from the fact that a comprehensive study including the entire core group ofZapornia, including the recently-extinct species (to the extent they could be sampled forancient DNA) has only been done once as of 2023, and the assessment relies on the limited molecular data available in 2002. While separating the Little crake in (sub)genusPalugalla has been proposed,[23] almost all subsequent autors preferred to retain all the core-group species inZapornia. However, the Henderson and Spotless crakes (and presumably some extinct species) stand apart from the Little and Baillon's crakes, and theirclade might also include the Black-tailed crake and indeed the Sakalava rail,[8] maybe even theLimnobaenus species.[20] If this group includes the extinctHawaiian rail, the subgenus namePennula would apply if theLimnobaenus lineage is not included. The proposedmonotypic generaAphanolimnas andNesophylax would probably be included here (andAphanolimnas would be the name of this group if split fromZapornia and ifPennula is affiliated withLimnobaenus and excluded from it), whilePorzanula, established for the now-extinctLaysan rail, is quite confidently a recent derivative of Baillon's crake's ancestors, and would warrant synonymization withZapornia no matter how this is circumscribed.[8][20]
The Brown crake has been variously assigned to theLimnocorax[8] orZaporniasensu lato[2][15] clades; as mentioned above, the bulk of its published mtDNA data is erroneous. Intriguingly, one study combining morphological and DNA data[20] found theIsabelline bush-hen – one of the species generally retained inAmaurornis today – to be closely allied to the Brown crake, and consequently also warranting inclusion inZapornia. This is not supported by the limited datasets analyzing correctly-sequenced mtDNA however,[8] and may be due to morphologicalconvergence.[7]
As mentioned above, a number of recently-extinct Pacific island rails are also assigned toZapornia nowadays:
| Image | Common name | Scientific name | Distribution |
|---|---|---|---|
 | Laysan rail | Zapornia palmeri Formerly inPorzana orPorzanula | Laysan (and introduced to Midway), Northwestern Hawaiian Islands, northern Polynesia; extinct mid-late 1944 |
 | Hawaiian rail | Zapornia sandwichensis Formerly inPennula orPorzana | Big Island of Hawaii, northeastern Polynesia; extinct ~1890 |
| Kosrae crake | Zapornia monasa Formerly inAphanolimnas orPorzana | Kosrae and possibly Ponapé, southern Micronesia; extinct mid-19th century | |
 | Tahiti crake | Zapornia nigra Formerly inNesophylax orPorzana | Tahiti, central Polynesia; extinct ~1800 |
The specimen used to describe the Tahiti crake has long been lost, quite likely even before it arrived at a museum, and thus the species' affiliations and even its very existenceremain conjectural until new material evidence is found. One original painting byGeorg Forster is presumed to document its former existence, but this has often been dismissed as depicting aSpotless or evenHenderson crake. If the Tahiti crake was indeed a distinct species, the specimen shown in the painting was part of a collection which also included (as perJohann Reinhold Forster's notes) Spotless crakes from Tahiti and Tonga, causing subsequent authors who had no access to the specimens to treat them all as a single species.[24]
The other three extinct species are known from numerous (Laysan rail) or very few (the other two) specimens. In the case of the Hawaiian rail, colour differences among these specimen caused them to be assigned to two species, but more likely they are simply juvenile and adult birds of a single species. What limitedancient DNA has been recovered from them allies the Laysan rail robustly with Baillon's and Little crakes (i.e. subgenusZapornia even in the most narrow circumscription) and the other two with the Spotless and Henderson crakes – which, if correct, would cause the (sub)genusPennula to refer to all of them if they are not included inZapornia.[14] Morphologically however, the Kosrae crake seems closer to the Black crake (though with considerable uncertainty)[7][25][26] while the Hawaiian rail is so similar to theLimnobaenus lineage that it might arguably be included in that subgenus (which would causeAphanolimnas to apply to the Spotless/Henderson/Kosrae crake group, if that is separated fromZaporniasensu stricto).[20]
In addition, a number of prehistorically extinct rails – most if not all flightless – known fromsubfossils found on oceanic islands have been placed intoPorzana. Their former range is not anywhere close to the present-day range ofPorzana proper (nor much closer to the knownfossil record of the genus), but within or closely adjacent to the range ofZapornia as attested by living and historically known species. Consequently, it is more likely that most of them are actuallyZapornia:[20]
The St. Helena crake has traditionally been considered an insular offshoot of ancestralBaillon's crakes[34] – basically theLaysan rail's equivalent from almost exactlythe other side of the world –, and is officially placed inZapornia by several authorities today.[11][12] However, even though no molecular data are available for it as of 2023, it has been included in several analyses of morphological and combined morphological-molecular datasets, which strongly suggest it is closerZapornia than toPorzana in the modern sense, but without actually being part ofZapornia.[7][20][25] Instead, it is more likely part of an Atlantic island radiation ofLaterallus (American crakes), which may also include theInaccessible Island rail (formerly inAtlantisia) and theAscension crake (at first included inAtlantisia but more recently separated asmonotypicgenusMundia), and perhaps forms aclade withinLaterallus with theBlack rail,Dot-winged, andGalapagos crakes.[20][35]
Of the Pacific island"Porzana" that have beencladistically studied in a combined morphological-molecular analysis,[20] theGreat andSmall Maui crakes are not only most likely to belong intoZapornia, but actually seem to be close relatives or evensister species within the group that also includes the Laysan rail and Baillon's crake.Ancient DNA was also recovered successfully from both species, and gave a different picture: The Small Maui crake, while being part of the coreZapornia, seems more closely related to theSpotless crake than to Baillon's crake. The Great Maui crake, however, could not be placed confidently in the analysis. Neither the rawDNA sequence data, not details regarding analytic methods, nor any results have been published except a brief summary, so no further conclusions can be drawn for the time being. However, regarding the Great Maui crake, the analyses took place at a time whenPorzana was still treatedsensu lato,Zapornia was not yet revalidated, andRallina was not yet revealed assister group ofZapornia but believed to be so distantly related as to be irrelevant for phylogenetic analyses of"Porzana".[36] Consequently, while the Small Maui crake is very likely aZapornia under all but the most extreme "splitter" taxonomies, the Great Maui crake probably belongs to a different branch ofZapornia, or represents a distinct lineage oftribeZapornini or evensubfamilyHimanthornithinae.
The extremely tinyLiliput crake fromMolokaʻi directly to the west of Maui, by contrast, turns out close toLaterallus in the combined analysis, but without obvious affiliations to any particular group of species in that genus. It might be part of aradiation that includesLaterallus as well asRufirallus and theOcellated crake from South America, and given thatLaterallus as traditionally circumscribed is probablyparaphyletic[10] it might thus even belong into an expandedRufiralllus. Since a purely morphological cladistic analysis[7] could not assign it (or any other prehistoric Hawaiian"Porzana", for that matter) to any particular lineage within Himanthornithinae, the Liliput crake's apparent similarity to tribeLaterallini might, on the other hand, simply be chanceconvergence.
TheGreat andSmall Oʻahu crakes did not turn up anywhere nearZapornia (norPorzana) in the morphological-molecular analysis,[20] but robustly fell within the other rail subfamilyRallinae. Therein they resolved in tribeRallini as well-distinct lineages within a radiation aroundGallirallus. The smaller species fell withinHypotaenidia (which nowadays contains the bulk of the Pacific island rails formerly included inGallirallus), while the larger one turned out morebasal, in a badly-resolved radiation of mid-sized to large and very often flightless species comprising numerous small genera. Remarkably, the samephylogenetic situation also occurred on theChatham Islands on the opposite end of the Pacific Ocean; there, however, the more ancient lineage (Chatham rail) evolved to diminutive size, while theHypotaenidia species (Dieffenbach's rail) became more robust than itsvolant ancestors.[2][9]
BothGreat Big Island crake andSmall Big Island crake are known from very few subfossil remains; they resemble theHawaiian rail but are about 10% larger/smaller in linear dimensions of their bones, which is well outside the known range of Hawaiian rail size variation. Ancient DNA was successfully extracted from the remains, which suggested a close relationship with the Hawaiian rail, the Spotless crake, and the Small Maui crake; as with the Maui rails, no data or detailed information were published.[36] Until more individuals of the extinct rails of the Big Island of Hawaiʻi are found, the exact relationships and even the distinctness of the two unnamed species remain elusive.[27]