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-19th century, when these rather terrestrial birds were recognized to form a genus distinct from the decidedly aquatic Rallus, the validity of Hypotaenidia has been disputed.

Hypotaenidia
Buff-banded rail, Hypotaenidia philippensis
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Gruiformes
Family:	Rallidae
Genus:	Hypotaenidia Reichenbach, 1853
Type species
Rallus pectoralis[1] Reichenbach, 1853
Species
8 living, and see text
Synonyms
Eulabeornis Nesoclopeus Stictolimnas (tentatively included here) and see text

Only in the 2010s has this question be resolved to some degree of satisfaction. While the present genus does indeed belong to the Gallirallus group in tribe Rallini of subfamily Rallinae, it stands apart from the numerous more basal lineages therein, and constitutes a well-distinct clade of smallish to mid-sized species distributed from Sahul far into the Pacific – across a range of at least 9,000 by 8,000 km (almost 6,000 by 5,000 miles). Like their larger more ancestral relatives, they readily evolve into flightless island endemics in the absence of terrestrial predators; however, their smaller bulk makes it easier for them to get airborne, and more prone to be swept away by strong winds. Consequently, they are (together with the Zapornia crakes) suspected to make up much of the prehistoric diversity of flightless rails of the oceanic islands of the Pacific.^[2][3]

Hypotaenidia rails are typically a brownish hue on the upperside; this can range from almost beige to blackish in lightness and generally tends toward reddish hues, and many species have light spots or stripes on the remiges or the entire wings; often, conspicuous light stripes run above and/or below the eyes. The underside is barred black-and-white in almost all members of this genus; unlike in the Zapornia crakes (which are also smaller on average, but with some overlap, and generally similar in coloration) this barring is not restricted to the area between legs and tail, but extends across the entire belly up to the neck. A few species are so cryptic that they appear almost uniformly medium to blackish-brown at a distance. The eyes are red to chestnut, and the bill and legs are either more or less bright red to yellowish, or blackish, usually in line with the overall darkness of the plumage.^[4]

Species

Genus Hypotaenidia, as circumscribed after the split-up of Gallirallus, contains the following species:^[5]

Extant

Image	Common name	Scientific name	Distribution
	Okinawa rail	Hypotaenidia okinawae	Okinawa, Japan
	Barred rail	Hypotaenidia torquata	the Philippines, Sulawesi (Indonesia) and Salawati (western New Guinea)
	Buff-banded rail	Hypotaenidia philippensis	Australasia and the southwestern Pacific region, including the Philippines, New Guinea, Australia and New Zealand
	Guam rail	Hypotaenidia owstoni	Guam
	Pink-legged rail	Hypotaenidia insignis	New Britain
	Roviana rail	Hypotaenidia rovianae	Western Province (the Solomon Islands)
	Woodford's rail	Hypotaenidia woodfordi	the Solomon Islands
	Lord Howe woodhen	Hypotaenidia sylvestris	Lord Howe Island

"Sharpe's rail" may be a melanistic Buff-banded rail

"Sharpe's rail" (traditionally Gallirallus sharpei) is the name given to a singular and enigmatic specimen, Naturalis Biodiversity Center RMNH 87485. Probably collected around 1860, the specimen seems to have arrived at the museum without any accompanying data. It has been suggested to be an aberrant individual of H. philippensis which it certainly resembles much in size, shape, and some plumage details; unpublished DNA data also indicates it belongs to this species. Consequently, it would belong in Hypotaenidia if Gallirallus is split.

Extinct

Several rail species that have gone extinct in fairly recent times and which were traditionally placed in Gallirallus are better assigned to Hypotaenidia:

Image	Scientific name	Common name	Distribution
	†Bar-winged rail	Hypotaenidia poeciloptera	Fiji (Viti Levu)
	†Dieffenbach's rail	Hypotaenidia dieffenbachii	the Chatham Islands
	†Tahiti rail	Hypotaenidia pacifica	Tahiti
	†Wake Island rail	Hypotaenidia wakensis	Wake Island

The aberrant Chatham rail may also belong in Hypotaenidia

The Chatham rail (Cabalus modestus) is another species that was usually included in Gallirallus in the genus' loose circumscription, and often considered a close relative of H. dieffenbachii with which it shared its island home. However, these two species are far less closely related than presumed, leading to reestablishment of the genus Cabalus when Gallirallus was split up. Even so, the Chatham rail is very closely related to the Hypotaenidia clade, and analyses are hampered by the lack of data from the extinct and little-known species. Some datasets do resolve the Chatham rail as member of Hypotaenidia, and it may eventually be moved here.^[2][3][6][7]

Also, many Pacific rails died out before they could be studied alive by scientists, and are not even attested by skin specimens, but only from fragmentary evidence such as subfossil bones or brief reports in travellers' accounts. They have been traditionally placed in Gallirallus, but most if not all would seem to belong elsewhere, and at least in the case of Polynesian species almost certainly in Hypotaenidia:^[8]

Melanesian species

• New Ireland rail, "Gallirallus" ernstmayri

This unidentified "ground bird" found on Norfolk Island around 1800 AD resembles Hypotaenidia species in shape and pattern

Micronesian species

• Tinian rail, "Gallirallus" pendiculentus
• Aguiguan rail, "Gallirallus" pisonii
• Rota rail, "Gallirallus" temptatus

Polynesian species

• Astolfo's rail, "Gallirallus" astolfoi^[8]
• Nuku Hiva rail, "Gallirallus" epulare^[9]
• Ua Huka rail, "Gallirallus" gracilitibia^[9]
• Niue rail, "Gallirallus" huiatua ^[10][11]
• Mangaia rail, "Gallirallus" ripleyi^[12]
• Tahuata rail, "Gallirallus" roletti^[9]
• Tubuai rail, "Gallirallus" steadmani^[13]
• Huahine rail, "Gallirallus" storrsolsoni
• Vava'u rail, "Gallirallus" vavauensis^[14]
• ʻEua rail, "Gallirallus" vekamatolu – possibly survived to the early 19th century^[15][16]
• Hiva Oa rail, ?"Gallirallus" sp.
• Norfolk Island rail, "Gallirallus" sp. - possibly survived to the early 19th century^[17]

In addition, the Small Oʻahu "crake" ("Porzana" ziegleri) is anatomically similar to Hypotaenidia and could have been be a Zapornis-sized species of the present genus, while the Snipe rail (Capellirallus karamu) of New Zealand might be closely enough related to the Chatham rail to be included in its genus, i.e. Hypotaenidia if Cabalus is considered invalid.^[6]