''Cabalus'' is a disputed

Oceania Oceania ( , ) is a region, geographical region including Australasia, Melanesia, Micronesia, and Polynesia. Outside of the English-speaking world, Oceania is generally considered a continent, while Mainland Australia is regarded as its co ...

n genus of

bird Birds are a group of warm-blooded vertebrates constituting the class (biology), class Aves (), characterised by feathers, toothless beaked jaws, the Oviparity, laying of Eggshell, hard-shelled eggs, a high Metabolism, metabolic rate, a fou ...

s in the family

Rallidae Rails (avian family Rallidae) are a large, Cosmopolitan distribution, cosmopolitan family (biology), family of small- to medium-sized terrestrial and/or semi-amphibious birds. The family exhibits considerable diversity in its forms, and includes ...

. Both species placed in the genus here were previously considered part of the genus ''

Gallirallus ''Gallirallus'' is a genus of Rallidae, rails that live in the Australasian-Pacific region. The genus is characterised by an ability to colonise relatively small and isolated islands and thereafter to evolve flightless forms, many of which beca ...

'', one was alternatively placed in ''Tricholimnas'' alone or together with the Lord Howe woodhen, and the other was initially included in ''

Rallus ''Rallus'' is a genus of wetland birds of the Rallidae, rail family. Sometimes, the genera ''Lewinia'' and ''Gallirallus'' are included in it. Six of the species are found in the Americas, and the three species found in Eurasia, Africa and Mada ...

''.

Species

As delimited here, the genus contains two species, one extinct and another possibly so:Garcia-R, Juan C. ''et al.'' (2014): Deep global evolutionary radiation in birds: Diversification and trait evolution in the cosmopolitan bird family Rallidae. '' Mol. Phylogenet. Evol.'' 81: 96–108.
PDF fulltext
/ref> * New Caledonian rail, ''Cabalus lafresnayanus'' (possibly

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

) – formerly in ''Gallirallus'' or ''Tricholimnas'' * Chatham rail, ''Cabalus modestus'' (extinct) – formerly in ''Gallirallus'' or ''Rallus'' These species occur on widely separate islands of the southwestern

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

region; as they are both distinct and singular lineages since at least about 5 million years ago, this may simply mean that they are (or were) the last survivors of a group that formerly spread across the

New Zealand New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...

region. However, other than being flightless Rallini with a drab brownish coloration, the two species are not much alike, their size difference being vast and running contrary to

Bergmann's Rule Bergmann's rule is an ecogeographical rule that states that, within a broadly distributed taxonomic clade, populations and species of larger size are found in colder environments, while populations and species of smaller size are found in warmer ...

, and their ecology – though barely studied and certainly restricted by the limited options on their respective island homes – also seems to have been quite different. The New Caledonian rail may in fact belong in ''Gallirallus'' (or indeed ''Tricholimnas''); whether it is more closely related to the Chatham rail or to the

weka The weka, also known as the Māori hen or woodhen (''Gallirallus australis'') is a flightless bird species of the rail family. It is endemic to New Zealand. Some authorities consider it as the only extant member of the genus '' Gallirallus''. ...

requires further study; analyses of different DNA datasets have yielded inconsistent results. The prehistoric Snipe rail of

, traditionally separated in a

monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unisp ...

genus ''Capellirallus'', seems crucial to determine this, as it is in all respects (except for its plumage, which is unknown) quite similar to the Chatham rail, except for being intermediate in size between the two supposed species of ''Cabalus''. It is even possible that the genus ''Cabalus'' will eventually be abolished again, since some DNA analyses place the Chatham rail within the large

evolutionary radiation An evolutionary radiation is an increase in taxonomic diversity that is caused by elevated rates of speciation, that may or may not be associated with an increase in morphological disparity. A significantly large and diverse radiation within ...

of smallish ''Gallirallus''-type species which forms the well-distinct

clade In biology, a clade (), also known as a Monophyly, monophyletic group or natural group, is a group of organisms that is composed of a common ancestor and all of its descendants. Clades are the fundamental unit of cladistics, a modern approach t ...

Hypotaenidia ''Hypotaenidia'' is a genus of birds in the family Rallidae. The genus is considered separate by the IOC and IUCN, while ''The Clements Checklist of Birds of the World'' / eBird consider the species to be part of ''Gallirallus''. Since the mid-19 ...

'', and the New Caledonian rail well outside of it. Kirchman, Jeremy J. (2012): Speciation of flightless rails on islands: A DNA-based phylogeny of the typical rails of the Pacific. ''

Auk Auks or alcids are birds of the family Alcidae in the order Charadriiformes. The alcid family includes the Uria, murres, guillemots, Aethia, auklets, puffins, and Brachyramphus, murrelets. The family contains 25 extant or recently extinct speci ...

'' 129(1):s 56–69.
PDF fulltext
/ref>Garcia-R, Juan C. & Matzke, Nicholas J. (2021): Trait-dependent dispersal in rails (Aves: Rallidae): Historical biogeography of a cosmopolitan bird clade. '' Mol. Phylogenet. Evol.'' 159: 107106.
PDF preprint
/ref>Kirchman, Jeremy J. ''et al.'' (2021): Phylogeny based on ultra-conserved elements clarifies the evolution of rails and allies (Ralloidea) and is the basis for a revised classification. ''

Ornithology Ornithology, from Ancient Greek ὄρνις (''órnis''), meaning "bird", and -logy from λόγος (''lógos''), meaning "study", is a branch of zoology dedicated to the study of birds. Several aspects of ornithology differ from related discip ...

'' 138(4): 1–21.
PDF fulltext
/ref>

References

Bird genera Bird genera with one living species {{Gruiformes-stub