A considerable literature was subsequently devoted to its possible affinities, with current researchers agreeing it was derived from the swamphen genus Porphyrio.

[5] 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.

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).

Schlegel argued that the discovery of the takahē showed that members of Porphyrio could be large, thereby disproving Strickland's earlier doubts based on size.

[8] 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.

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.

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.

[15] 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.

[7] The British ecologist Anthony S. Cheke considered previous arguments about the bird's affinities in 1987, and supported it being a Porphyrio relative, while noting that there were two further contemporary accounts.

[12] 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".

While it may have been derived from Africa or Madagascar, genetic studies have shown that other rails have dispersed to unexpectedly great distances from their closest relatives, making alternative explanations possible.

[7] Rothschild stated he had the Dutch artist John Gerrard Keulemans depict it as intermediate between the takahē and Aptornis, which he thought its closest relatives.

At least in the latter part of its existence, it appears to have been confined to mountains (retreating there between the 1670s and 1705), in particular to the Plaine des Cafres plateau, situated at an altitude of about 1,600–1,800 m (5,200–5,900 ft) in south-central Réunion.

The small Mauritian flying fox and the snail Tropidophora carinata lived on Réunion and Mauritius before vanishing from both islands.

[4] 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.

[12] 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.

There are also some curious birds, which never descend to the sea-side, and who are so little accustomed to, or alarmed at, the sight of man, that they suffer themselves to be killed by the stroke of a walking stick.