Réunion swamphen
The Réunion swamphen, also known as the Réunion gallinule or oiseau bleu, is a hypothetical extinct species of rail that was endemic to the Mascarene island of Réunion. While only known from 17th and 18th accounts by visitors to the island, it was scientifically named in 1848, based on the 1674 account by Sieur Dubois. A considerable literature was subsequently devoted to its possible affinities, with current researchers agreeing it was derived from the swamphen genus Porphyrio. It has been considered mysterious and enigmatic due to the lack of any physical evidence of it existence.
Described as entirely blue in plumage with a red beak and legs, and being the size of a Réunion ibis or chicken, which could mean in length, the Réunion swamphen may have been similar to the takahe. While easily hunted, it was a fast runner and able to fly, though reluctantly. It may have fed on plant matter and invertebrates, as other swamphens, and was said to nest among grasses and aquatic ferns. It was only found on the Plaine des Cafres plateau, where it may have retreated to during the latter part of its existence, whereas other swamphens inhabit lowland swamps. While the last unequivocal account is from 1730, it may have survived until 1763, but overhunting and the introduction of cats probably drove it to extinction.
Taxonomy
Visitors to the Mascarene island of Réunion during the 17th and 18th centuries reported blue birds, referred to in French as oiseau bleu. The first such account is that of the French traveller Sieur Dubois, who was on Réunion from 1669 to 1672. The British naturalist Hugh Edwin Strickland stated in 1848 that he would have thought Dubois' account referred to a Porphyrio swamphen if not for its large size and other features. Strickland expressed hope that remains of this and other extinct Mascarene birds would be found there. In a response to Strickland's book later that year, the Belgian scientist Edmond de Sélys Longchamps coined the scientific name Apterornis coerulescens based on Dubois' account. The specific name is Latin for "bluish, becoming blue". Selys Longchamps also included two other Mascarene birds at the time only known from contemporary accounts in the genus Apterornis; the Réunion ibis and the red rail. He thought them related to the dodo and Rodrigues solitaire, due to their shared rudimentary wings, tail, and disposition of their digits., which Walter Rothschild later believed to have been a relative
The name Apterornis had already been used for a different extinct bird genus from New Zealand by the British biologist Richard Owen earlier in 1848, and the French biologist Charles Lucien Bonaparte coined the new binomial Cyanornis erythrorhynchus for the oiseau bleu in 1857. The same year, the German ornithologist Hermann Schlegel moved the species to the genus Porphyrio, as P. caerulescens, indicating an affinity with the takahe of New Zealand. The then recent discovery of the takahe showed that members of Porphyrio could be large, thereby disproving Strickland's earlier doubts based on size. The British ornithologist Richard Bowdler Sharpe simply used the name Porphyrio caerulescens in 1894. The British zoologist Walter Rothschild retained the name Apterornis for the bird in 1907, and considered it similar to Aptornis and the takahe, believing Dubois' account indicated it was related to those birds. The Japanese ornithologist Masauji Hachisuka used the new combination Cyanornis coerulescens for the bird in 1953, also considering it akin to the takahe due to its size.
The bird was subsequently mainly classified as a member of Porphyrio or Notornis throughout the 20th century, and the latter genus was eventually itself considered a junior synonym of Porphyrio. In 1967, the American ornithologist James Greenway stated that the bird "must remain mysterious" until Porphyrio bones are one day uncovered. In 1974, an attempt was made to find fossil localities on the Plaine des Cafres plateau, where the bird was said to have lived, but no caves were found, and it was determined that a more careful study of the area was needed before excavations could be made. In 1977, the American ornithologist Storrs L. Olson found the old accounts consistent with an endemic derivative of Porphyrio, and considered it a probable species whose remains might one day be discovered. Considering previous arguments about the bird's affinities, the British ecologist Anthony S. Cheke supported that the bird was a Porphyrio relative in 1987, and made notice of two more contemporary accounts. The same year, the British writer Errol Fuller listed the bird as a hypothetical species, and expressed puzzlement as to how a considerable literature had been derived from such "flimsy material".
The French palaeontologist Cécile Mourer-Chauviré and colleagues listed the bird as Cyanornis caerulescens in 2006, indicating the uncertainty of its classification. They stated the reason no fossils of it had been found was probably because it did not live in the parts of Réunion where fossils can be obtained. Cheke and the British palaeontologist Julian P. Hume stated in 2008 that since the mystery of the "Réunion solitaire" had been solved after it was identified with ibis remains, the Réunion swamphen remains the most enigmatic of the birds from the old accounts. In his 2012 book about extinct birds and his 2019 monograph about the extinct Mascarene rails, Hume considered the Réunion swamphen "perhaps the most enigmatic of all rails" with no evidence to resolve its taxonomy, yet he considered it to be no doubt a derivative of Porphyrio'', as the all blue colouration is only found in that genus among rails. While it may have been derived from Africa or Madagascar, genetic studies have shown that other rails have dispersed unexpectedly far in distance from their closest relatives, making alternate explanations possible.
Description
The Réunion swamphen was described as having entirely blue plumage with a red beak and legs, and is generally agreed to have been a large, terrestrial swamphen, with features indicative of reduced flight capability, such as larger size and more robust legs. There has been disagreement over the size of the bird, as Dubois' account compared its size with that of a Réunion ibis while that of the French engineer Jean Feuilley from 1704 compared it to a domestic chicken. Cheke stated in 1987 that Feuilley's account would indicate the bird was not unusually large, perhaps the size of a swamphen. Hume pointed out in 2019 that the Réunion ibis would have been at most, similar to the extant African sacred ibis, while chickens could be in length, and that there was therefore no contradiction. The Réunion swamphen would thereby have been about the same size as the takahe.The first description of the Réunion swamphen is that of Dubois from 1674, which reads as follows:
The last definite account of the bird is that of the priest Brown from around 1730 :
Olson stated the comparison to a "wood pigeon" was a reference to the common wood pigeon, implying that Brown described it as smaller than Dubois did, while Hume suggested it could be the extinct Réunion blue pigeon. The 1708 account of Hébert does not add much information about the bird, though he qualified its colouration as "dark blue".
While the bird is only known from written accounts, reconstructions of it appear in Rothschild's 1907 book Extinct Birds, and Hachisuka's 1953 book The Dodo and Kindred Birds. Rothschild stated he had the Dutch artist John Gerrard Keulemans depict it as intermediate between the takahe and Aptornis, which he thought its closest relatives. Fuller found Frohawk's illustration to be a well-produced work, though almost entirely conjectural in depicting it like a slimmed-down takahe.
Behaviour and ecology
Little is known about the ecology of the Réunion swamphen; it was easily caught and killed, unlike other swamphens, though it was able to run fast. While some early researchers thought the bird to be flightless, Brown's account states it could fly, and it is thought to have been a reluctant flier. Hume suggested it may have fed on plant matter and invertebrates, as other swamphens do. At least in the latter part of its existence, it appears to have been confined to mountains, in particular to the Plaine des Cafres plateau, situated at an altitude of about in south-central Réunion. The environment of this area consists of open woodland in a subalpine forest steppe, and has marshy pools.The species was termed a land-bird by Dubois, while other swamphens inhabit lowland swamps in contrast. This is similar to the Réunion ibis, which lived in forest rather than wetlands, which is otherwise typical ibis habitat. Cheke and Hume proposed that the ancestors of these birds colonised Réunion before swamps had developed, and had therefore become adapted to the available habitats. They were perhaps prevented from colonising Mauritius as well due to the presence of red rails there, which may have occupied a similar niche.
Feuilley described some characteristics of the bird in 1704:
The only account of its nesting behaviour is that of La Roque from 1708:
Many other endemic species on Réunion became extinct after the arrival of humans and the resulting disruption of the island's ecosystem. The Réunion swamphen lived alongside other now-extinct birds, such as the Réunion ibis, the Mascarene parrot, the Hoopoe starling, the Réunion parakeet, the Réunion owl, the Réunion night heron, and the Réunion pink pigeon. Extinct Réunion reptiles include the Réunion giant tortoise and an undescribed Leiolopisma skink. The small Mauritian flying fox and the snail Tropidophora carinata lived on Réunion and Mauritius before vanishing from both islands.
Extinction
Many terrestrial rails are flightless, and island populations are particularly vulnerable to man-made changes; as a result, rails have suffered more extinctions than any other family of birds. All six endemic species of Mascarene rails are extinct, caused by human activities. While the last unequivocal account of the Réunion swamphen is from 1730, an anonymous account from 1763, possibly by the British Brigadier-General Richard Smith, may be the last mention of the bird, though it does not describe it, and could apply to other species. It is also impossible to say whether this writer saw the bird himself. It gives a contemporary impression of the Réunion swamphen's habitat, Plaine des Cafres, and of how birds were hunted there:, the only place this bird was said to live
If the Réunion swamphen survived until 1763 this would be far longer than many other extinct birds of Réunion, probably due to its remote habitat. Overhunting was the main cause of its extinction, but according to Cheke and Hume, the introduction of cats at the end of the 17th century would have led to the elimination of the bird once these became feral and reached its habitat. Today, cats are still a serious threat to native birds, in particular Barau's petrel, since they occur all over Réunion, including the most remote and high peaks. The eggs and chicks would also have been vulnerable after the accidental introduction of rats in 1676. On the other hand, the Réunion swamphen and other birds of the island appear to have successfully survived feral pigs. Cattle grazing on Plaine des Cafres was promoted by the French explorer Jean-Baptiste Charles Bouvet de Lozier in the 1750s, which may have had an impact on the bird.