The Réunion ibis or Réunion sacred ibis (Threskiornis solitarius) is an extinct species of ibis that was endemic to the volcanic island of Réunion in the Indian Ocean. The first subfossil remains were found in 1974, and the ibis was first scientifically described in 1987. Its closest relatives are the Malagasy sacred ibis, the African sacred ibis, and the straw-necked ibis. Travellers' accounts from the 17th and 18th centuries described a white bird on Réunion that flew with difficulty and preferred solitude, which was subsequently referred to as the "Réunion solitaire".
In the mid 19th century the old travellers' accounts were incorrectly assumed to refer to white relatives of the dodo. This was assumed because one of the accounts specifically mentioned dodos on the island, and 17th-century paintings of white dodos had recently surfaced. Additionally, both it and the Rodrigues solitaire, an actual dodo relative, were referred to as "solitaires" due to shared habits. However, no fossils referable to dodo-like birds were ever found on Réunion, and it was later questioned whether the paintings had anything to do with the island. Other identities were suggested as well, based only on speculations. In the late 20th century, the discovery of ibis subfossils led to the idea that the old accounts actually referred to an ibis species instead. The idea that the "solitaire" and the subfossil ibis are identical was met with limited dissent, but is now widely accepted.
Combined, the old descriptions and subfossils show that the Réunion ibis was mainly white, with this colour merging into yellow and grey. The wing tips and plumes of ostrich-like feathers on its rear were black. The neck and legs were long, and the beak was relatively straight and short for an ibis. It was more robust in build than its extant relatives, but was otherwise quite similar to them. It would have been no longer than 65 cm (25 in) in length. Subfossil wingbones indicate it had reduced flight capabilities, a feature perhaps linked to seasonal fattening. The diet of the Réunion ibis was worms and other items foraged from the soil. In the 17th century, it lived in mountainous areas, but it may have been confined to these remote heights by heavy hunting by humans and predation by introduced animals in the more accessible areas of the island. Visitors to Réunion praised its flavour, and therefore sought after its flesh. These factors are believed to have driven the Réunion ibis to extinction by the early 18th century.
Taxonomy The taxonomic history of the Réunion ibis is convoluted and complex, due to the ambiguous and meagre evidence that was available to scientists until the late 20th century. The supposed "white dodo" of Réunion is now believed to have been an erroneous conjecture based on the few contemporary reports which described the Réunion ibis, combined with paintings of white dodos from Mauritius by the Dutch painters Pieter Withoos and Pieter Holsteyn II (and derivatives) from the 17th century that surfaced in the 19th century.
Contemporary accounts The English Chief Officer John Tatton was the first to mention a specifically white bird on Réunion, in 1625. The French occupied the island from 1646 and onwards, and referred to this bird as the "solitaire". M. Carré of the French East India Company described the "solitaire" in 1699, explaining the reason for its name:
François Leguat, a marooned French Huguenot, used the name "solitaire" for the Rodrigues solitaire, a Raphine bird (related to the dodo) he encountered on the nearby island of Rodrigues in the 1690s, but it is thought he borrowed the name from a 1689 tract by Marquis Henri Duquesne which mentioned the Réunion species. Duquesne himself had probably based his own description on an earlier one. No specimens of the "solitaire" were ever preserved.
The two individuals Carré attempted to send to the royal menagerie in France did not survive in captivity. Billiard claimed that the French administrator Bertrand-François Mahé de La Bourdonnais sent a "solitaire" to France from Réunion around 1740. Since the Réunion ibis is believed to have gone extinct by this date, the bird may actually have been a Rodrigues solitaire.
The only contemporary writer who referred specifically to "dodos" inhabiting Réunion was the Dutch sailor Willem Ysbrandtszoon Bontekoe, though he did not mention their colouration:
When his journal was published in 1646, it was accompanied by an engraving which is now known to have been copied after one of the dodos in the Flemish painter Roelant Savery's "Crocker Art Gallery sketch". Since Bontekoe was shipwrecked and lost all his belongings after visiting Réunion in 1619, he may not have written his account until he returned to Holland, seven years later, which would put its reliability in question. He may have concluded in hindsight that it was a dodo, finding what he saw similar to accounts of that bird.
Early interpretation
In the 1770s, the French naturalist Comte de Buffon stated that the dodo inhabited both Mauritius and Réunion for unclear reasons. He also combined accounts about the Rodrigues solitaire and a bird from Mauritius ("oiseau de Nazareth", now thought to be a dodo), as well as the "solitaire" Carré reported from Réunion under one "solitaire" section, indicating he believed there was both a dodo and "solitaire" on Réunion. The English naturalist Hugh Edwin Strickland discussed the old descriptions of the "solitaire" in his 1848 book The Dodo and Its Kindred, and concluded it was distinct from the dodo and Rodrigues solitaire due to its colouration.
The Belgian scientist Edmond de Sélys Longchamps coined the scientific name Apterornis solitarius for the "solitaire" in 1848, apparently making it the type species of the genus, in which he also included two other Mascarene birds only known from contemporary accounts, the red rail and the Réunion swamphen. As the name Apterornis had already been used for a different bird by the English biologist Richard Owen, and the other former names were likewise invalid, Bonaparte coined the new binomial Ornithaptera borbonica in 1854 (Bourbon was the original French name for Réunion). In 1854, the German ornithologist Hermann Schlegel placed the "solitaire" in the same genus as the dodo, and named it Didus apterornis. He restored it strictly according to contemporary accounts, which resulted in an ibis or stork-like bird instead of a dodo.
In 1856, William Coker announced the discovery of a 17th-century "Persian" painting of a white dodo among waterfowl, which he had been shown in England. The artist was later identified as Pieter Withoos, and many prominent 19th-century naturalists subsequently assumed the image depicted the white "solitaire" of Réunion, a possibility originally proposed by ornithologist John Gould. Simultaneously, several similar paintings of white dodos by Pieter Holsteyn II were discovered in the Netherlands. Other paintings and drawings were also later identified as showing white dodos. In 1869, the English ornithologist Alfred Newton argued that the Withoos' painting and engraving in Bontekoe's memoir depicted a living Réunion dodo that had been brought to Holland, while explaining its blunt beak as a result of beak trimming to prevent it from injuring humans. He also brushed aside the inconsistencies between the illustrations and descriptions, especially the long, thin beak implied by one contemporary account.
Newton's words particularly cemented the validity of this connection among contemporary peers, and several of them expanded on his views. The Dutch zoologist Anthonie Cornelis Oudemans suggested in 1917 that the discrepancies between the paintings and the old descriptions were due to the paintings showing a female, and that the species was, therefore, sexually dimorphic. The British zoologist Walter Rothschild claimed in 1907 that the yellow wings might have been due to albinism in this particular specimen, since the old descriptions described these as black.
By the early 20th century, many other paintings and even physical remains were claimed to be of white dodos, amid much speculation. Rothschild commissioned British artist Frederick William Frohawk to restore the "solitaire" as both a white dodo, based on the Withoos painting, and as a distinct bird based on the French traveller Sieur Dubois' 1674 description, for his 1907 book Extinct Birds. In 1937, the Japanese writer Masauji Hachisuka suggested that the old accounts and paintings represented two different species, and referred to the white dodos of the paintings as Victoriornis imperialis (honouring King Victor Emmanuel III of Italy), and the "solitaire" of the accounts as Ornithaptera solitarius (using the generic name coined by Bonaparte). Hachisuka also suggested that a 1618 Italian illustration previously identified as a dodo being hunted, actually showed a male, brown Réunion solitaire (he ruled out Rodrigues because that island was not yet inhabited at the time). To him, this cleared up the confusion between the two species, which is why he named the white dodo for the King of Italy (the illustration being from Italy). Today the illustration is thought to depict an ostrich or a bustard.
Modern interpretation
Until the late 1980s, belief in the existence of a white dodo on Réunion was the orthodox view, and only a few researchers doubted the connection between the "solitaire" accounts and the dodo paintings. The American ornithologist James Greenway cautioned in 1958 that no conclusions could be made without solid evidence such as fossils, and that nothing indicated that the white dodos in the paintings had anything to do with Réunion. In 1970, the American ornithologist Robert W. Storer predicted that if any such remains were found, they would not belong to Raphinae like the dodo and Rodrigues solitaire (or even to the pigeon family like them).
The first subfossil bird remains on Réunion, the lower part of a tarsometatarsus, was found in 1974, and considered a new species of stork in the genus Ciconia by the British ornithologist Graham S. Cowles in 1987. The remains were found in a cave, which indicated it had been brought there and eaten by early settlers. It was speculated that the remains could have belonged to a large, mysterious bird described by Leguat, and called "Leguat's giant" by some ornithologists. "Leguat's giant" is now thought to be based on a locally extinct population of greater flamingos. Also in 1987, a subfossil tarsometatarsus of an ibis found in a cave was described as Borbonibis latipes (the specific name means "wide foot") by the French palaeontologists Cécile Mourer-Chauviré and François Moutou, and thought related to the bald ibises of the genus Geronticus.