The Réunion Flightless Ibis (Threskiornis solitarius) is an extinct bird species that was native to the island of Réunion. It is probably the same bird discovered by Portuguese sailors there in 1613 and until recently assumed by biologists to be a member of the solitaire family, who called it the "Réunion Solitaire" (Raphus solitarius) and classified it as a relative of the Dodo.

That bird was at various times classified as Victoriornis imperialis (the "Réunion Solitaire" or "White Dodo" of descriptions and paintings - the latter obviously show an albino dodo from Mauritius) and Borbonibis latipes (from the first ibis bones found, before a connection to the solitaire reports had been made). The epithet solitarius derives from the Raphus solitarius description of Baron Edmund de Sélys-Longchamps in 1848, but the species' existence was not confirmed until the discovery of bones on Réunion in the late 20th century. The discovery that it actually was an ibis perfectly fits what the early travellers said about its plumage and habits. The confusion can be explained by the fact that solitaire was used by the writers of the descriptions as a descriptive term regarding to a birds' solitary habits, which the ibis happened to share with the Rodrigues Solitaire, but was interpreted by the scientists as an indication of a taxonomic relationship.

The last account of the "Réunion Solitaire" was recorded in 1705, indicating that the species probably became extinct sometime early in that century.

The vernacular name is misleading, since travellers' reports as well as bone measurements indicate that it was well on its way to flightlessness, but could still fly some distance after a running take-off.