Réunion swamphen

Hypothetical extinct species of bird

The Réunion swamphen (Porphyrio caerulescens), also known as the Réunion gallinule or oiseau bleu (French for "blue bird"), is a hypothetical extinct species of rail that was endemic to the Mascarene island of Réunion. While only known from 17th and 18th century 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 its existence. This bird was described as entirely blue in plumage with a red beak and legs. It was said to be the size of a Réunion ibis or chicken, which could mean in length, and it may have been similar to the takahē. While easily hunted, it was a fast runner and able to fly, though it did so reluctantly. It may have fed on plant matter and invertebrates, as do other swamphens, and was said to nest among grasses and aquatic ferns. It was only found on the Plaine des Cafres plateau, to which it may have retreated 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 likely drove it to extinction.

Visitors to the Mascarene island of Réunion during the 17th and 18th centuries reported blue birds (oiseaux bleus in French). The first such account is that of the French traveller Sieur Dubois, who was on Réunion from 1669 to 1672, which was published in 1674. Responding 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". Sélys Longchamps also included two other Mascarene birds, at the time only known from contemporary accounts, in the genus Apterornis: the Réunion ibis (now Threskiornis solitarius); and the red rail (now Aphanapteryx bonasia). He thought them related to the dodo and Rodrigues solitaire, due to their shared rudimentary wings, tail, and the disposition of their digits. 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 takahē, believing Dubois's account indicated it was related to those birds. The Japanese ornithologist Masauji Hachisuka used the new combination Cyanornis coerulescens for the bird in 1953 (with the specific name misspelled), also considering it related to the takahē due to its size. Some writers equated the bird with extant swamphens, including African swamphens by the French ornithologist Jacques Berlioz in 1946, and western swamphens by the French ornithologist Nicolas Barré in 1996, despite their different habitat. The French ornithologist Philippe Milon doubted the Porphyrio affiliation in 1951, since Dubois's account stated the Réunion bird was palatable, while extant swamphens are not. In 1974, an attempt was made to find fossil localities on the Plaine des Cafres plateau, where the bird was said to have lived. No caves, which might contain kitchen middens where early settlers discarded bones of local birds, 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. 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". 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 Mascarene birds from the old accounts.

Little is known about the ecology of the Réunion swamphen; it was easily caught and killed, unlike other swamphens (which avoid predators by flying or hiding), though it was able to run fast.

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, all caused by human activities. Overhunting was the main cause of the Réunion swamphen's extinction (it was considered good game and was easy to catch), but according to Cheke and Hume, the introduction of cats at the end of the 17th century could have contributed 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 to rats after their accidental introduction 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 also had an impact on the bird. 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 this bird, though no description of it was provided, and it might refer to another 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:

If the Réunion swamphen survived until 1763 this would be far longer than many other extinct birds of Réunion. If so, its survival was likely because of the remoteness of its habitat.