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.

We wished to keep two of these birds to send to France and present them to His Majesty, but as soon as they were on board ship, they died of melancholy, having refused to eat or drink.

[3]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".

[5] 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.

[3] 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.

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.

[13] 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.

[15][16] 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).

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).

[2][18][19] 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.

[20] 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.

[2] In 1995, the French ecologist Jean-Michel Probst reported his discovery of a bird mandible during an excavation on Réunion the former year, and suggested it may have belonged to the ibis or the "solitaire".

The authors pointed out that the contemporary descriptions matched the appearance and behaviour of an ibis more than a member of the Raphinae, especially due to its comparatively short and straight mandible, and because ibis remains were abundant in some localities; it would be strange if contemporary writers never mentioned such a relatively common bird, whereas they mentioned most other species subsequently known from fossils.

[24] The possible origin of the 17th-century white dodo paintings was examined, by the Spanish biologist Arturo Valledor de Lozoya in 2003, and independently by experts of Mascarene fauna Cheke and Julian Hume in 2004.

According to the aforementioned writers, it appears these pictures were themselves derived from a whitish dodo in a previously unreported painting called Landscape with Orpheus and the Animals, produced by Roelant Savery c. 1611.

Cheke and Hume concluded the painted specimen was white due to albinism, and that this peculiar feature was the reason it was collected from Mauritius and brought to Europe.

[2] Valledor de Lozoya instead suggested that the light plumage was a juvenile trait, a result of bleaching of old taxidermy specimens, or simply due to artistic license.

[5] The British writer Errol Fuller agrees that the 17th-century paintings do not depict Réunion birds, but has questioned whether the ibis subfossils are necessarily connected to the "solitaire" accounts.

[5] Contemporary accounts described the species as having white and grey plumage merging into yellow, black wing tips and tail feathers, a long neck and legs, and limited flight capabilities.

[24] Cheke and Hume have suggested that the French word (bécasse) from Dubois' original description, usually translated to "woodcock", could also mean oystercatcher, another bird with a long, straight, but slightly more robust, bill.

[7] Subfossils of the Réunion ibis show that it was more robust, likely much heavier, and had a larger head than the African sacred and straw-necked ibises.

It was perhaps flightless, but this has not left significant osteological traces; no complete skeletons have been collected, but of the known pectoral elements, only one feature indicates reduction in flight capability.

[2] The only mention of its diet and exact habitat is the account of the French cartographer Jean Feuilley from 1708, which is also the last record of a living individual: The solitaires are the size of an average turkey cock, grey and white in colour.

During the five or six days that we were allowed to go into the woods, so many were killed that our General [de La Haye] was constrained to forbid anyone going beyond a hundred paces from the camp for fear the whole quarter would be destroyed, for one needed only to catch one bird alive and make it cry out, to have in a moment whole flocks coming to perch on people, so that often without moving from one spot one could kill hundreds.

But, seeing that it would have been impossible to wipe out such a huge quantity, permission was again given to kill, which gave great joy to everyone, because very good fare was had at no expense.

[4] In the 1820s, the French navigator Louis de Freycinet asked an old slave about drontes (old Dutch word for dodo), and was told the bird existed around Saint-Joseph when his father was an infant.

Cheke and Hume suspect that feral cats initially hunted wildlife in the lowlands and later turned to higher inland areas, which were probably the last stronghold of the Réunion ibis, as they were unreachable by pigs.