Réunionibis

The Réunion Ibis (Threskiornis solitarius) is an extinct species of ibis that was endemic to the island of Réunion, east of Madagascar in the Indian Ocean.

Systematik

In the 19th century, accounts from the 17th and 18th centuries describing white "Solitaire" birds on Réunion with reduced flight capabilities were assumed to refer to white relatives of the Dodo, due to one account specifically mentioning Dodos, and because 17th century paintings of white Dodos had recently surfaced. The Réunion Solitaire was thus classified as a member of the pigeon subfamily Raphinae, and even placed in the same genus as the Dodo by some authors. The discrepancies between the Dodo paintings and the contemporary accounts also lead some authors to believe that two distinct white raphine birds had lived on Réunion; one Dodo-like bird, and one species similar to the Rodrigues Solitaire.

No raphine fossils were ever found on Réunion, and it was later questioned whether the paintings had anything to do with the island. In the late 20th century, the discovery of a subfossil species of ibis lead to the idea that the accounts actually referred to this bird. This species had a relatively straight beak, and may have had difficulty flying. The ibis was classified as a member of the genus Threskiornis, of which it is the only known extinct species. Its closest relatives are the African Sacred Ibis and the Straw-necked Ibis. The idea that the Solitaire and the subfossil ibis are identical has met limited dissent since it was proposed.

Combined, the old accounts and subfossils show that the Réunion Ibis was mainly white, with this colour merging into yellow and grey. The wing tips were black, and so were the ostrich-like feathers covering its rear. The neck and legs were long, the beak was relatively straight and short for an ibis, and comparable to that of a Woodcock. Its diet was worms and other items foraged in soil. It had difficulty flying, a feature perhaps linked to seasonal fat-cycles. It lived in remote, mountainous areas, but this was perhaps a result of hunting by humans and their introduced animals, who arrived on the island in the 17th century. These factors are believed to have wiped out the Réunion Ibis by the early 18th century.

Taxonomy

Pieter Withoos's painting of a white Dodo among various birds

The taxonomic history of the Réunion Ibis is very convoluted, due to the ambiguous and meagre evidence that was available to scientists until recently. The supposed "white Dodo" of Réunion is now believed to have been an erroneous conjecture based on the few known contemporary reports of the Réunion Ibis, combined with paintings of white Dodos by Pieter Withoos and Pieter Holsteyn II (and derivatives of them) from the 1600s, that surfaced in the 19th century.

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: Vorlage:Quotation When his journal was published in 1646, it was accompanied by an engraving copied after one of the Dodos in Roelant Savery's "Crocker Art Gallery sketch". Since Bontekoe was shipwrecked and lost all his belongings after visiting Réunion in 1619, he would not had been able to write his account until seven year later when he returned to Holland. It is likely that he wrote it from memory, and it may therefore not be entirely reliable.

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 the bird as the "Solitaire". The marooned Huguenot François Leguat used the name "Solitaire" for the raphine bird he encountered on the nearby island of Rodrigues in the 1690s, but it is thought he borrowed the name from a tract which mentioned the Réunion species. M. Carré of the French East Indies Company described the Réunion Solitaire in 1699, explaining the reason for its name:

One of Pieter Holsteyn II's three paintings of a white Dodo

No specimens of the bird were ever collected. The two Solitaires Carré attempted to send to the royal menagerie in France did not survive in captivity. It has been claimed that 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.

In the 1770s, Comte de Buffon stated the Dodo inhabited both Mauritius and Réunion, but the basis for this claim is unknown. Hugh Edwin Strickland discussed the old descriptions of the Réunion Solitaire in his 1848 book The Dodo and Its Kindred, and concluded it was distinct from the Dodo and Rodrigues Solitaire. Baron Edmund 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. In 1854, 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. As the name Apterornis had already been used for a different bird by 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).

Restoration of the Réunion Solitaire by Frederick William Frohawk, a hybrid between Dubois' account and the Rodrigues Solitaire

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, including John Gould, Alfred Newton, and Walter Rothschild, subsequently assumed the image depicted the white Solitaire of Réunion. Simultaneously, several similar paintings of white Dodos by Pieter Holsteyn II were discovered in the Netherlands. The images were thought to have been drawn after the same live bird, but they are clearly copied from each other, and Withoos likely copied his Dodo from one of Holsteyn's works, since these were probably produced at an earlier date. All other white Dodo pictures are thought to be based on these paintings. Anthonie Cornelis Oudemans suggested that the discrepancies between the paintings and the old descriptions were due the paintings showing a female, and that the species was therefore sexually dimorphic. Rothschild claimed the yellow wings might had been due to albinism in this particular specimen. By the early 20th century, many other paintings and even physical remains were claimed to be white Dodos, and much speculation was generated on such dubious grounds. Some believed the Solitaire of the old descriptions was rather a species similar to the Rodrigues Solitaire. In 1953, Masauji Hachisuka went as far as referring to the white Dodos of the paintings as Victoriornis imperialis, and the Solitaire of the accounts as Ornithaptera solitarius.

Modern identification

Until the late 1980s, only a few researchers doubted the connection between the Solitaire accounts and the Dodo paintings. They cautioned that no conclusions could be made without solid evidence such as fossils, and that nothing indicated the paintings had anything to do with Réunion. In 1970, Robert W. Storer predicted that if any such remains were found, they would not belong to Raphinae, or even columbidae.

The first subfossil bird remains on Réunion were found in 1974, and assigned to a stork, Ciconia sp. In 1987, subfossils of a recently extinct species of ibis from Réunion were described as Borbonibis latipes, and thought related to the bald ibises of the genus Geronticus. In 1994, the "stork" remains were shown to belong to this ibis as well. The 1987 discovery lead Anthony Cheke to suggest to one of the describers, Francois Moutou, that the subfossils may have been of the Réunion Solitaire. This suggestion was published by the describers of Borbonibis in 1995, and they also reassigned it to the genus Threskiornis, now combined with the specific epithet solitarius from de Sélys-Longchamps' 1848 binomial for 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 since a fragment of a comparatively short and straight ibis mandible was discovered in 1994, 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. Morphological study suggested its closest relatives are the African Sacred Ibis (T. aethiopicus) of Africa and the Straw-necked Ibis (T. spinicollis) of Australia. The African Sacred Ibis also has similar coloured plumage to that described in the old descriptions of the Réunion Solitaire.

Roelant Savery painting with a whitish Dodo in the lower right, 1611

The possible basis for the 17th century white Dodo paintings has also recently been determined by Arturo Valledor de Lozoya in 2003, and independently by experts of Mascarene fauna Anthony S. Cheke and Julian Hume in 2004. According to these authors, it appears that the pictures were derived from a previously unreported painting containing a whitish Dodo, called Landscape with Orpheus and the animals, produced by Roelant Savery in ca. 1611. The Dodo was apparently based on a stuffed specimen then in Prague; a walghvogel described as having a "dirty off-white colouring" was mentioned in an inventory of specimens in the Prague collection of the Holy Roman Emperor Rudolf II to whom Savery was contracted at the time (1607–1611). Savery's several later Dodo images all show greyish birds, possibly because he had by then seen a normal specimen. 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. 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.

Since Réunion was not visited by Europeans until 1635, the 1611 painting could not have shown a bird from there. Furthermore, Réunion island is only three million years old, whereas Mauritius and Rodrigues, with each their raphine species, are eight to ten million years old, and it is unlikely that either bird would have been capable of flying after five or more million years of adapting to their islands. Therefore it is unlikely that Réunion could have been colonised by flightless birds from these islands, and only flighted species on the island have relatives there. No fossil remains of Dodo-like birds have ever been found on the island.

A few later sources have taken issue with the proposed ibis-identity of the Solitaire, and have even regarded the "white Dodo" as a valid species. Errol Fuller agrees the 17th century paintings do not depict Réunion birds, but has questioned whether the ibis subfossils are necessarily connected to the "Solitaire" accounts. He notes that no evidence indicates the extinct ibis survived until the time Europeans reached Réunion.

Description

A close extant relative, the African Sacred Ibis

Contemporary accounts described the "Solitaire" as having white and grey plumage merging into yellow, black wing tips and tail feathers, a long neck and legs, and limited flight capabilities. Sieur D. B. Dubois' 1674 account is the most detailed description of the bird:

The plumage colouration mentioned is similar to that of the African Sacred Ibis and the Straw-necked Ibis, which are also mainly white and glossy black. In the reproductive season, the ornamental feathers on the back and wing tips of the African Sacred Ibis look similar to the feathers of an ostrich, which echoes Dubois' description. Likewise, a subfossil lower jaw found in 1994 showed that the bill of the Réunion Ibis was relatively short and straight for an ibis, which corresponds with Dubois' Woodcock comparison.

The known 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 nonetheless very similar to them in most features. Rough protuberances in the wing bones of the Réunion Ibis are similar to those of birds that use their wings in combat. 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. The coracoid is elongated and the radius and ulna are robust, as in flighted birds, but a particular foramen between a metacarpal and the alular is otherwise only known from flightless birds, such as some ratites, penguins, and several extinct species. As contemporary accounts are inconsistent on whether the Solitaire was flightless or had some flight capability, Mourer-Chauvire suggested that this was dependent on fat-cycles; it was described as being "fat", so perhaps it could not fly when it was so, but could when it was thin.

Behaviour and ecology

The Straw-necked Ibis, another close relative

The Réunion Ibis Solitaire in the forest and was termed a land-bird by Dubois, so it did not live in typical ibis habitats such as wetlands. It has been proposed that this is because the ancestors of the bird colonised Réunion before swamps had developed, and had therefore became irreversibly adapted to the habitats present at that time. They were perhaps prevented from colonising Mauritius as well due to the presence of Red Rails there, which may have occupied a similar niche. It appears it lived in high altitudes, and perhaps had a limited distribution.

The only mention of its diet and exact habitat is Feuilley's account from 1708, which is also the last record of the bird:

The diet and mode of obtaining it matches that of an ibis, whereas members of the Raphinae are known to have been frugivorous.

Accounts by early visitors indicate the Solitaire was found near their landing sites, but they were found only in remote places by 1667. The bird may have survived in eastern lowlands until the 1670s. Though many late 1600s accounts state the Solitaire was good food, Feuilley stated the bird tasted bad. This may be because the bird changed its diet when it moved to more rugged, higher terrain, to escape pigs that destroyed their nests; since it had limited flight capabilities, it likely nested on the ground.

Many other of the endemic species of Réunion became extinct after the arrival of man, so the ecosystem of the island is heavily damaged. The Réunion Ibis lived alongside other recently extinct birds such as the Hoopoe Starling, the Mascarene Parrot, the Réunion Parakeet, the Réunion Swamphen, the Réunion Owl, the Réunion Night Heron, and the Réunion Pink Pigeon. Extinct reptiles include the Réunion giant tortoise and the Mauritian giant skink. The small Mauritian flying fox and the snail Tropidophora carinata lived on Réunion and Mauritius, but vanished from both islands.

Extinction

As Réunion was populated, the Réunion Ibis appears to have become confined to the tops of mountains. Introduced predators such as cats and rats had an impact on the ibis. Overhunting also contributed, and several contemporary accounts state the bird was hunted for food in large numbers. In 1625, John Tatton described the tameness of the Solitaires and how easy it was to hunt, as well as the large quantity consumed: Vorlage:Quotation

Forested mountain tops on inland Réunion

In 1671, Melet described the slaughter of several types of birds on the island, and mentioned the culinary quality of the Solitaire: Vorlage:Quotation

The last definite account of the "Solitaire" of Réunion was Feuilley's from 1708, indicating that the species probably became extinct sometime early in the century. In the 1820s, Louis Henri 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. This would perhaps be around 1710-15, but the account may be unreliable. Anthony Cheke and Julian Hume suspect that feral cats turned to higher inland areas, which were unreachable by pigs, once they had wiped out the wildlife in the lowlands. The ibis would then had been exterminated around 1710-15.

External links

Wikispecies: Threskiornis solitarius – Artenverzeichnis

• The Dodo – The merging of myth and reality: Half hour video interview with expert Julian Hume about the white Dodo