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Extinct species of rail from Lord Howe Island

The white swamphen (Porphyrio albus), also known as the Lord Howe swamphen, Lord Howe gallinule or white gallinule, is an extinct species of rail which lived on Lord Howe Island, east of Australia. It was first encountered when the crews of British ships visited the island between 1788 and 1790, and all contemporary accounts and illustrations were produced during this time. Today, two skins exist: the holotype in the Natural History Museum of Vienna, and another in Liverpool's World Museum. Although historical confusion has existed about the provenance of the specimens and the classification and anatomy of the bird, it is now thought to have been a distinct species endemic to Lord Howe Island and most similar to the Australasian swamphen. Subfossil bones have also been discovered since. The white swamphen was long. Both known skins have mainly white plumage, although the Liverpool specimen also has dispersed blue feathers. This is unlike other swamphens, but contemporary accounts indicate birds with all white, all blue, and mixed blue and white plumage. The chicks were black, becoming blue and then white as they aged. Although this has been interpreted as due to albinism, it may have been progressive greying in which feathers lose their pigment with age. The bird's bill, frontal shield and legs were red, and it had a claw (or spur) on its wing. Little was recorded about the white swamphen's behaviour. It may not have been flightless, but was probably a poor flier. This and its docility made the bird easy prey for visiting humans, who killed it with sticks. Reportedly once common, the species may have been hunted to extinction before 1834, when Lord Howe Island was settled.

Lord Howe Island is a small, remote island about east of Australia. Ships first arrived on the island in 1788, including two which supplied the British penal colony on Norfolk Island and three transport ships of the British First Fleet. When passed the island, the ship's commander named it after First Lord of the Admiralty Richard Howe. Crews of the visiting ships captured native birds (including white swamphens), and all contemporary descriptions and depictions of the species were made between 1788 and 1790. The bird was first mentioned by the master of HMS Supply, David Blackburn, in a 1788 letter to a friend. Other accounts and illustrations were produced by Arthur Bowes Smyth, the fleet's naval officer and surgeon, who drew the first known illustration of the species; Arthur Phillip, governor of New South Wales; and George Raper, midshipman of Secondhand accounts also exist, and at least ten contemporary illustrations are known. The accounts indicate that the population varied, and individual bird plumage was white, blue, or mixed blue and white. The binomial name in White's book, Fulica alba, was provided by the English naturalist George Shaw. The specific name is derived from the Latin word for white (albus). White found the bird most similar to the western swamphen (Porphyrio porphyrio, then in the genus Fulica). Although he apparently never visited Lord Howe Island, White may have questioned sailors and based some of his description on earlier accounts. He said he had described a skin at the Leverian Museum, and his book included an illustration of the specimen by the artist Sarah Stone. It is uncertain when (and how) the specimen arrived at the museum. This skin, the holotype specimen of the species, was purchased by the Natural History Museum of Vienna in 1806 and is catalogued as specimen NMW 50.761. The naturalist John Latham listed the bird as Gallinula alba in a later 1790 work, and wrote that it may have been a variety of purple swamphen (or "gallinule"). The zoologist Coenraad Jacob Temminck assigned the white swamphen to the swamphen genus Porphyrio as P. albus in 1820, and the zoologist George Robert Gray considered it an albino variety of the Australasian swamphen (P. melanotus) as P. m. varius alba in 1844. The belief that the bird was simply an albino was held by several later writers, and many failed to notice that White cited Lord Howe Island as the origin of the Vienna specimen. In 1873, the naturalist Osbert Salvin agreed that the Lord Howe Island bird was similar to the takahē, although he had apparently never seen the Vienna specimen, basing his conclusion on a drawing provided by von Pelzeln. Salvin included a takahē like illustration of the Vienna specimen by the artist John Gerrard Keulemans, based on von Pelzeln's drawing, in his article. In 1875, the ornithologist George Dawson Rowley noted differences between the Vienna and Liverpool specimens and named a new species based on the latter: P. stanleyi, named after Lord Stanley. He believed that the Liverpool specimen was a juvenile from Lord Howe Island or New Zealand, and continued to believe that the Vienna specimen was from Norfolk Island. Despite naming the new species, Rowley considered the possibility that P. stanleyi was an albino Australasian swamphen and considered the Vienna bird more similar to the takahē. In 1901, the ornithologist Henry Ogg Forbes had the Liverpool specimen dismounted so he could examine it for damage. Forbes found it similar enough to the Vienna specimen to belong to the same species, N. alba. The zoologist Walter Rothschild considered the two species distinct from each other in 1907, but placed them both in the genus Notornis. Rothschild thought that the image published by Phillip in 1789 depicted N. stanleyi from Lord Howe Island, and the image published by White in 1790 showed N. alba from Norfolk Island. He disagreed that the specimens were albinos, thinking instead that they were evolving into a white species. Rothschild published an illustration of N. alba by Keulemans where it is similar to a takahē, inaccurately showing it with dark primary feathers, although the Vienna specimen on which it was based is all white. In 1913, after examining the Vienna specimen, Iredale concluded that the bird belonged in the genus Porphyrio and did not resemble the takahē. In 1928, the ornithologist Gregory Mathews discussed a 1790 painting by Raper which he thought differed enough from P. albus in proportions and colouration that he named a new species based on it: P. raperi. Mathews also considered P. albus distinct enough to warrant a new genus, Kentrophorina, due to having a claw (or spur) on one wing. In 1936, he conceded that P. raperi was a synonym of P. albus. In 1941, the biologist Ernst Mayr proposed that the white swamphen was a partially albinistic population of Australasian swamphens. Mayr suggested that the blue swamphens remaining on Lord Howe Island were not stragglers, but had survived because they were less conspicuous than the white ones. In 1967, the ornithologist James Greenway also considered the white swamphen a subspecies (with P. stanleyi a synonym) and considered the white individuals albinos. He suggested that the similarities between the wing feathers of the white swamphen and the takahē were due to parallel evolution in two isolated populations of reluctant fliers. The ornithologist Sidney Dillon Ripley found the white swamphen to be intermediate between the takahē and the purple swamphen in 1977, based on patterns of the leg scutes, and reported that X rays of bones also showed similarities with the takahē. He considered only the Vienna specimen to be a white swamphen, whereas he considered the Liverpool specimen to be an albino Australasian swamphen (listing P. stanleyi as a junior synonym of that bird) from New Zealand. In 1991, the ornithologist Ian Hutton reported subfossil bones of the white swamphen. Hutton agreed that the birds described as having white and blue feathers were hybrids between the white swamphen and the Australasian swamphen, an idea also considered by the ornithologists Barry Taylor and Ber van Perlo in 2000. The ornithologists Hein van Grouw and Julian P. Hume concluded in 2016 that many of the old accounts had errors in the bird's provenance, that it was endemic to Lord Howe Island, and suggested when the specimens were collected (between March and May 1788) and under which circumstances they arrived in England. They concluded that the white swamphen was a valid species which changed colouration with age, after reconstructing the colouration of juvenile birds before turning white (which was distinct from other swamphens). Van Grouw and Hume found the white swamphen anatomically more similar to the Australasian swamphen than the Philippine swamphen, and suggested that studies with more complete data sets than the earlier DNA might yield different results. Due to their anatomical similarities, geographic proximity and the recolonisation of Lord Howe and Norfolk Island by Australasian swamphens, they found it likely that the white swamphen was descended from Australasian swamphens.

The length of the white swamphen has been given as 36 cm (14 in) and 55 cm (22 in), making it similar to the Australasian swamphen in size. Its wings were proportionally the shortest of all swamphens. The wing of the Vienna specimen is mm long, the tail is , the culmen with its frontal shield (the fleshy plate on the head) is , the tarsus is , and the middle toe is long. The wing of the Liverpool specimen is long, the tarsus is and the middle toe is Its tail and beak are damaged, and cannot be reliably measured. The white swamphen differed from most other swamphens (except the Australasian swamphen) in having a short middle toe; it is the same length as the tarsus, or longer, in other species. The white swamphen's tail was also the shortest. Both specimens have a claw (or spur) on their wings; it is longer and more discernible in the Vienna specimen, and sharp and buried in the feathers of the Liverpool specimen. This feature is variable among other kinds of swamphen. The softness of the rectrices (tail feathers) and the lengths of the secondary and wing covert feathers relative to the primary feathers appear to have been intermediate between those of the purple swamphen and the takahē. Blackburn's 1788 account is the only one that mentions the diet of this bird:
blockquote|  On the shore we caught several sorts of birds  and a white fowl – something like a Guinea hen, with a very strong thick & sharp pointed bill of a red colour – stout legs and claws – I believe they are carnivorous they hold their food between the thumb or hind claw & the bottom of the foot & lift it to the mouth without stopping so much as a parrot. Upon the discovery of subfossil pelvic and limb bones in 2021, Hume and colleagues preliminarily stated that these bones were much more robust in the white swamphen than in the volant Australasian swamphen, a trait common in flightless rails.

Although the white swamphen was considered common during the late 18th century, it appears to have disappeared quickly; the period from the island's discovery to the last mention of living birds is only two years (1788–90). It had probably vanished by 1834, when Lord Howe Island was first settled, or during the following decade. Whalers and sealers had used the island for supplies, and may have hunted the bird to extinction. Habitat destruction probably did not play a role, and animal predators (such as rats and cats) arrived later. In 1789, White described how the white swamphen could be caught:
blockquote|They [sailors] also found on it, in great plenty, a kind of fowl, resembling much of the Guinea fowl in shape and size, but widely different in colour; they being in general all white, with a red fleshy substance rising, like a cock’s comb, from the head, and not unlike a piece of sealing wax. These not being birds of flight, nor in the least wild, the sailors availing themselves of their gentleness and inability to take wing from their pursuits, easily struck them down with sticks. Eight types of bird have become extinct due to human interference since Lord Howe Island was discovered, including the Lord Howe pigeon (Columba vitiensis godmanae), the Lord Howe parakeet (Cyanoramphus subflavescens), the Lord Howe gerygone (Gerygone insularis), the Lord Howe fantail (Rhipidura fuliginosa cervina), the Lord Howe thrush (Turdus poliocephalus vinitinctus), the robust white eye (Zosterops strenuus) and the Lord Howe starling (Aplonis fusca hulliana). The extinction of so many native birds is similar to extinctions on several other islands, such as the Mascarenes.