Rodrigues solitaire

Rodrigues Solitaire Temporal range: Recent
Only known drawing by someone who observed the bird in life (François Leguat, 1708)
Conservation status
Extinct (by 1778)  (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Order:	Columbiformes
Family:	Columbidae
Subfamily:	Raphinae
Genus:	Pezophaps Strickland, 1848
Species:	P. solitaria
Binomial name
Pezophaps solitaria (Gmelin, 1789)
Former range
Synonyms
Didus solitarius Gmelin, 1789 Pezophaps solitarius Strickland, 1848 Didus nazarenus Bartlett, 1851 Pezophaps minor Strickland, 1852

The Rodrigues Solitaire (Pezophaps solitaria) is an extinct, flightless bird that was endemic to the Mascarene island of Rodrigues, east of Madagascar in the Indian Ocean. Genetically nested within pigeons and doves, it was most closely related to the also extinct Dodo of Mauritius (the two forming the subfamily Raphinae). The Nicobar Pigeon is their closest living genetic relative.

The size of a swan, the Rodrigues Solitaire demonstrated pronounced sexual dimorphism. Males were much larger than females and measured up to 90 centimetres (35 inches) in length and 28 kilograms (62 pounds) in weight, contrasting with 70 centimetres (28 inches) and 17 kilograms (37 pounds) for females. Its plumage was grey and brown; the female was paler than the male. It had a black band at the base of its slightly hooked beak, and its neck and legs were long. Both sexes were highly territorial, with large bony knobs on their wings that were used in combat. The Rodrigues Solitaire laid a single egg, that was incubated in turn by both sexes. Gizzard stones helped digest its food, which included fruit and seeds.

First mentioned during the 17th century, the Rodrigues Solitaire was described in detail by François Leguat (leader of a group of French Huguenot refugees who were marooned on Rodrigues in 1691–1693). It was hunted by humans and introduced animals, and was extinct by the late 1700s. Apart from Leguat's account and drawing, and a few other contemporary descriptions, nothing was known about the bird until a few subfossil bones were found in a cave in 1789. Thousands of bones have subsequently been excavated. It is the only extinct bird with a former star constellation named after it, Turdus Solitarius.

Taxonomy and evolution

Skeleton of a male at Museum of Zoology, Cambridge

François Leguat was the first to refer to the bird as the "Solitaire" (referring to its solitary habits), but it has been suggested that he borrowed the name from a tract mentioning the Réunion Solitaire. The bird was first scientifically named as a species of Dodo (Didus solitarius, based on Leguat's description) by Johann Friedrich Gmelin in the thirteenth edition of Systema Naturae.

Hugh Edwin Strickland and Alexander Gordon Melville suggested the common descent of the Solitaire and the Dodo in 1848. They dissected the only known Dodo specimen with soft tissue, comparing it with the few Solitaire remains then available. Strickland stated that although not identical, these birds shared many distinguishing features in the leg bones otherwise only known in pigeons. The fact that the Solitaire laid only one egg, fed on fruits, was monogamous and cared for its nestlings also supported this relationship. Strickland recognized its generic distinction and named the new genus Pezophaps ("pedestrian pigeon" in ancient Greek). The differences between the sexes of the bird were so large that Strickland thought they belonged to two species, naming the smaller bird Pezophaps minor. Later study of skeletal features by Alfred and Edward Newton indicated that the Solitaire was morphologically intermediate between the Dodo and ordinary pigeons, but differed from them in its unique wrist-knob.

For a long time the Dodo and the Rodrigues Solitaire (collectively termed "didines") were placed in a family of their own, the Raphinae; this was because their relationships to other pigeons was unresolved. They were also placed in a monotypic family each, Raphidae and Pezophapidae, respectively, due to the suggestion that hey had evolved their similar features independently. Recently, osteological and molecular data led to the dissolution of the family Raphidae, and the Dodo and Solitaire were placed in their own subfamily, Raphinae, nested within the Columbidae.

Comparison of mitochondrial cytochrome b and 12S rRNA sequences isolated from the femur of a Rodrigues Solitaire and the tarsal of a Dodo confirmed their close relationship, and their placement within the Columbidae. Genetic evidence was interpreted to show that the Southeast Asian Nicobar Pigeon is their closest living relative, followed by Crowned Pigeons of New Guinea, and the superficially Dodo-like Tooth-billed Pigeon from Samoa. The following cladogram, from Shapiro et al. (2002), shows the Dodo's closest relationships within Columbidae, a clade consisting of generally ground-dwelling island endemics.

	Goura victoria (Victoria Crowned Pigeon) Caloenas nicobarica (Nicobar Pigeon) Pezophaps solitaria (Rodrigues Solitaire) Raphus cucullatus (Dodo) Didunculus strigirostris (Tooth-billed Pigeon)

A similar cladogram was published in 2007, differing in the inverted placement of Goura and Dicunculus, as well as the inclusion of the Pheasant Pigeon and the Thick-billed Ground Pigeon at the base of the clade. The 2002 study indicated that the ancestors of the Solitaire and the Dodo diverged around the Paleogene-Neogene boundary. The Mascarene Islands (a group of islands in the Indian Ocean east of Madagascar, that includes Mauritius and Réunion) are of volcanic origin and less than 10 million years old, so both birds' ancestors likely remained capable of flight long after the separation of their lineages. The lack of mammalian herbivores competing for resources on these islands allowed the Solitaire and the Dodo to attain large size.

A few reports mention other "Solitaires" from the Mascarenes. The term was also used for other species with "solitary" habits, such as the Réunion Ibis. Some scientists believed that Réunion was home to not only a white Dodo but also a white Solitaire (both of which are now believed to be misinterpretations of old reports). An atypical 17th-century description of a Dodo and bones found on Rodrigues (now known to have belonged to the Rodrigues Solitaire) led Abraham Dee Bartlett to name a new species, Didus nazarenus; it is now a junior synonym of this species.

Description

Restoration by Frederick William Frohawk, 1907

One observer described the Rodrigues Solitaire as the size of a swan. Sexual size dimorphism in this species is perhaps the greatest in any carinate bird. Males were considerably larger than females, measuring 90 cm (35 inches) in length and weighing up to 28 kg (62 pounds), whereas females were 70 cm (28 inches) and weighed 17 kg (37 pounds). Their weight may have varied substantially due to fat cycles, meaning that individuals were fat during cool seasons, but slim during hot seasons, and may have been as low as 21 kg in males and 13 kg in females. Their plumage was grey and brown. Females were paler than males and had light-coloured elevations on the lower neck. A black band (an original description says frontlet) appears on its head just behind the base of its beak. Its beak was slightly hooked, and its neck and legs were long. The skull was 170 millimetres (6.7 in) long, flattened at the top with the fore and hind parts elevated into two bony ridges structured with cancellous bone.

Both sexes possessed a large a tuberous knob of bone situated at the base of the carpometacarpus of each wrist. The knobs were about half the length of the metacarpus, and were larger in males than females. In life, these knobs would have been covered by tough skin and used as weapons.

The Solitaire shared traits with the Dodo (its closest relative) such as size and features in the skull, pelvis and sternum. It differed in other aspects; it was taller and more slender than the Dodo and had a smaller skull and beak, a flatter skull roof and larger orbits. Its neck and legs were proportionally longer, and the Dodo did not possess a wrist-knob equivalent. Many skeletal features of the Solitaire and Dodo that are unique among pigeons have evolved to adapt to flightlessness. Their pelvic elements were thicker than those of flighted birds (to support their greater weight), and their pectoral region and wings were paedomorphic (underdeveloped, retaining juvenile features). However, the skull, trunk and pelvic limbs were peramorphic (changing considerably with maturity).

Contemporary descriptions

Skeletons of female and male

Apart from François Leguat's rather simple depiction, the live appearance of the Rodrigues Solitaire is only known from a handful of descriptions; no soft-tissue remains survive. Leguat devoted three pages of his memoirs to the Solitaire, and was clearly impressed by the bird. He described its appearance as follows:

Of all the Birds in the Island the most remarkable is that which goes by the name of the solitary, because it is very seldom seen in company, tho' there are abundance of them. The Feathers of the Males are of a brown grey Colour: the Feet and Beak are like a Turkey's, but a little more crooked. They have scarce any Tail, but their Hind-part covered with Feathers is roundish, like the Crupper [rump] of a horse; they are taller than Turkeys. Their Neck is straight, and a little longer in proportion than a Turkey's when it lifts up his Head. Its Eye is Black and lively, and its Head without Comb or Cop. They never fly, their Wings are too little to support the Weight of their Bodies; they serve only to beat themselves, and flutter when they call one another. They will whirl about for twenty or thirty times together on the same side, during the space of four or five minutes. The motion of their Wings makes then a noise very like that of a Rattle; and one may hear it two hundred Paces off. The Bone of their Wing grows greater towards the Extremity, and forms a little round Mass under the Feathers, as big as a Musket Ball. That and its Beak are the chief Defence of this Bird. 'Tis very hard to catch it in the Woods, but easie in open Places, because we run faster than they, and sometimes we approach them without much Trouble. From March to September they are extremely fat, and taste admirably well, especially while they are young, some of the Males weigh forty-five Pounds.

Wing bones, including wrist-knobs (87–90) in the middle right

Several of Leguat's observations were confirmed through study of subfossil Solitaire remains. The wrist-knobs he described were confirmed. Also, a ridged surface appears at the base of the beak (indicating the position of the caruncular ridge, which Leguat described as a "widow's peak"). The curved contour lines of the pelvis also support the roundness of its hind parts, which he compared to that of a horse. Before fossils of the wrist-knob were found, Strickland noted that the keel of the sternum of the Solitaire was so well-developed as to almost indicate it had possessed the power of flight; however, since the humerus was very short he inferred that this was instead related to Leguat's claim that they used their wings for defence.

Leguat continued with an elaborate description of the female Solitaire (which also appears to be the sex depicted in his illustration of the bird):

The Females are wonderfully beautiful, some fair, some brown; I call them fair, because they are the colour of fair Hair. They have a sort of Peak, like a Widow's upon their Breasts [beaks], which is of a dun colour. No one Feather is straggling from the other all over their Bodies, they being very careful to adjust themselves, and make them all even with their Beaks. The Feathers on their Thighs are round like Shells at the end, and being there very thick, have an agreeable effect. They have two Risings on their Craws [crop] and the Feathers are whiter than the rest, which livelily represents the fine neck of a Beautiful Woman. They walk with so much Stateliness and good Grace, that one cannot help admiring them and loving them; by which means their fine Mein often saves their Lives.

Skull of male (1–3) and female (4–5) Rodrigues Solitaires

It has been proposed that Leguat's comparison between the crop of the female Solitaire and the "beautiful bosom of a woman" (changed to "fine neck" in some editions of his memoirs) was out of longing for female companionship.

Another description of appearance and behaviour is found in an anonymous document rediscovered in 1874 called Relation de l'Ile Rodrigue, which has been attributed to Julien Tafforet (who was marooned on Rodrigues in 1726):

The solitaire is a large bird, which weighs about forty or fifty pounds. They have a very big head, with a sort of frontlet, as if of black velvet. Their feathers are neither feathers nor fur; they are of light grey colour, with a little black on their backs. Strutting proudly about, either alone or in pairs, they preen their plumage or fur with their beak, and keep themselves very clean. They have their toes furnished with hard scales, and run with quickness, mostly among the rocks, where a man, however agile, can hardly catch them. They have a very short beak, of about an inch in length, which is sharp. They, nevertheless, do not attempt to hurt anyone, except when they find someone before them, and, when hardly pressed, try to bite him. They have a small stump of a wing, which has a sort of bullet at its extremity, and serves as a defence.

Behaviour and ecology

Observations of the Solitaire indicate that breeding pairs were highly territorial. They presumably settled disputes by striking each other with their wings; to aid this purpose, they used the knobs on their wrists. It has been suggested that the knobs may have been formed through continuous injuries, as they resemble diseased bone. Fractures in their wing bones also indicate that they were used in combat. It has also been suggested that these fractures may have been the result of a hereditary bone disease rather than battle-injuries. Some evidence (including their large size and the fact that tropical and frugivorous birds have slower growth rates) indicates that the bird may have had a protracted development period. Several accounts state that they defended themselves with a powerful bite. The species may have lived primarily in the island's woodlands, rather than on the shores.

The most detailed account of their habits is Leguat's. He described mating and nesting as follows:

Leguat's map of his settlement on Rodrigues containing Rodrigues Solitaires (many in pairs)

When these Birds build their Nests, they choose a clean Place, gather together some Palm-Leaves for that purpose, and heap them up a foot and a half high from the Ground, on which they sit. They never lay but one Egg, which is much bigger than that of a Goose. The Male and Female both cover it in their turns, and the young is not hatch'd till at seven Weeks' end: All the while they are sitting upon it, or are bringing up their young one, which is not able to provide itself in several Months, they will not suffer any other Bird of their Species to come within two hundred Yards round of the Place; But what is very singular, is, the Males will never drive away the Females, only when he perceives one he makes a noise with his Wings to call to the Female, and she drives the unwelcome Stranger away, not leaving it till 'tis without her Bounds. The Female do's the same as to the Males, whom she leaves to the Male, and he drives them away. We have observ'd this several Times, and I affirm it to be true.

The Combats between them on this occasion last sometimes pretty long, because the Stranger only turns about, and do's not fly directly from the Nest. However, the others do not forsake it till they have quite driven it out of their Limits. After these Birds have rais'd their young One, and left it to itself, they are always together, which the other Birds are not, and tho' they happen to mingle with other Birds of the same Species, these two Companions never disunite. We have often remark'd, that some Days after the young leaves the Nest, a Company of thirty or forty brings another young one to it, and the now fledg'd Bird, with its Father and Mother joyning with the Band, march to some bye Place. We frequently follow'd them, and found that afterwards the old ones went each their way alone, or in Couples, and left the two young ones together, which we call'd a Marriage.

Eighteenth, thirteenth, and twelfth vertebrae and left foot

The clutch was described as consisting of a single egg; given the bird's large size, this led to proposals that the Solitaire was K-selected (producing a low number of altricial offspring, requiring extensive parental care until maturity). The gathering of unrelated juveniles suggests that they formed crèches, that may have followed foraging adults as part of the learning process.

Sternum of a female and male

The size difference between sexes has led to the suggestion that the Solitaire was not monogamous as stated by Leguat, and that this deeply-religious man attributed the trait to the bird for moral reasons. It has been proposed that it was instead polygynous, and the wing-rattling behaviour described for males suggests lek-mating (where males gather for competitive mating display). However, size dimorphism occurs in some monogamous birds; most other pigeons are monogamous as well.

Tafforet's account of aggressive behaviour confirms Leguat's description, adding that Solitaires would even attack humans approaching their chicks:

They do not fly at all, having no feathers to their wings, but they flap them, and make a great noise with their wings when angry, and the noise is something like thunder in the distance. They only ly, as I am led to suppose, but once in the year, and only one egg. Not that I have seen their eggs, for I have not been able to discover where they lay. But I have never seen but one little one alone with them, and, if any one tried to approach it, they would bite him very severely. These birds live on seeds and leaves of trees, which they pick up on the ground. They have a gizzard larger than the fist, and what is surprising is that there is found in it a stone of the size of a henn's egg, of oval shape, a little flattened, although this animal cannot swallow anything larger than a small cherry-stone. I have eaten them: they are tolerably well tasted.

Pierre-André d'Héguerty, writing about his time on the island around 1735, stated that a captive Solitaire (which he described as having a melancholic appearance) would always walk in the same line until running out of space, and then return back.

Diet

Pelvis of female (1) and male (2), furcula (3) and gizzard stone (4–6)

Leguat stated that the Rodrigues Solitaire fed on dates, whereas Tafforet mentioned seeds and leaves. No other accounts mention diet. It has been suggested it ate latan palm fruits, for which it competed with the now-extinct Cylindraspis tortoises. It is not known how the young were fed, but related pigeons provide crop milk. The risings on the crop of the female may have covered glands that produced the crop milk. If the theory is correct, the birds may have practiced a division of labour, where the female stayed and fed the young crop milk, while the male collected food in the crop and delivered it to the female. It has been suggested that the maximum size attained by the Solitaire and the Dodo was limited by the amount of crop milk they were able to produce for their young during early growth.

Several contemporary accounts state that the Solitaire used gizzard stones. Dodos also did this, which may imply a similar diet. Leguat described the stones in the following passage (mentioning that Solitaires refused to feed in captivity):

Tho' these Birds will sometimes very familiarly come up near enough to one, when we do not run after them, yet they will never grow Tame. As soon as they are caught they shed Tears without Crying, and refuse all sustenance till they die.

We find in the Gizzards of both Male and Female, a brown Stone, of the bigness of a Hen's Egg, 'tis somewhat rough, flat on one side and round on the other, heavy and hard. We believe this Stone was there when they were hatched, for let them be never so young, you meet with it always. They never have but one of 'em, and besides, the Passage from the Craw to the Gizard is so narrow, that a like Mass of half Bigness cou'd not pass. It serv'd to whet our Knives better than any other Stone Whatsoever.

In 1877 three stones were found in a cavern on Rodrigues (each near a Solitaire skeleton), and were inferred to be the gizzard stones mentioned by Leguat. One of the stones was examined and found to be dolerite: somewhat rough, hard and heavy, ca. 50 g. (1 3/4 oz.), but hardly flat on one side as described by Leguat. This could be due to its association with a young individual. Although Leguat asserted that the bird hatched with the gizzard stone already inside, in reality adults most likely fed stones to hatchlings.

Relationship with humans

Frontpiece to Leguat's 1708 memoir, showing his settlement in Rodrigues (and a Solitaire in the middle)

Sir Thomas Herbert was the first to mention that "Dodos" lived on Rodrigues in 1634 (most likely referring to the Solitaire), and "Dodos" were again mentioned in 1700.

The next account (the first referring to the bird as the "Solitaire") was published in François Leguat's 1708 memoir, A New Voyage to the East Indies. Leguat was the leader of a group of nine French Huguenot refugees, who were the first to colonise the island (from 1691 to 1693) after they were abandoned there by their captain. He described the bird in some detail, including its behaviour. The Huguenots praised the birds for their flavour (especially the young), and used their gizzard stones as knife sharpeners (D'Héguerty claimed these were also useful in medicine). Leguat's observations are considered some of the first cohesive accounts of animal behaviour in the wild. He later left for Mauritius, but was too late to observe Dodos there.

Leguat's map of Rodrigues; his settlement can be seen to the northeast. Rodrigues Solitaires are sprinkled all over the map.

Many old accounts mention that Solitaires were hunted by man. Writing in 1735, Gennes de la Chancelière described the capture and consumption of two specimens as follows:

Our men told of having seen goats and a large quantity of birds of different kinds: they brought, amongst others, two of which were bigger by a third than the largest turkey; they appeared, nevertheless to be still quite young, still having down on the neck and head; their wingtips were but sparsely feathered, without any proper tail. Three sailors told me of having seen two others, of the same species, as big as the biggest ostrich. The young ones that were brought had the head made more or less like the latter animal, but their feet were similar to those of turkeys, instead of that of the ostrich which is forked and cloven in the shape of a hind's foot. These two birds, when skinned, had an inch of fat on the body. One was made into a pie, which turned out to be so tough that it was uneatable.

Japetus Steenstrup noted that some Solitaire remains bore traces of having been broken by man (or perhaps another large predator) to extract bone marrow.

Unlike the Dodo, no Rodrigues Solitaires are known to have been sent to Europe alive. However, it has been claimed that Bertrand-François Mahé de La Bourdonnais sent a "Solitaire" to France from the nearby island of Réunion around 1740. Since the Réunion Solitaire is believed to have gone extinct by this date, the bird may actually have been a Rodrigues Solitaire.

Extinction

First known Solitaire bones (1789)

In 1755, Joseph-François Charpentier de Cossigny attempted to obtain a live specimen, as he had been assured the Solitaire still survived in remote areas of the island. Though trying for 18 months, and offering large rewards, none could be found. He noted that cats were blamed for decimating the species, but suspected that it was due to hunting by humans instead.

The Rodrigues Solitaire probably became extinct sometime between the 1730s and 1760s; the exact date is unknown. Its disappearance coincided with the tortoise trade between 1730 and 1750; traders burnt off vegetation, hunted Solitaires and imported cats and pigs (that preyed on eggs and chicks).

Mounted skeleton, photographed ca. 1870

Alexandre Guy Pingré did not encounter any Solitaires when he visited Rodrigues to observe the 1761 transit of Venus, although he had been assured they survived. His friend, Pierre Charles Le Monnier, named a constellation, Turdus Solitarius, after the bird to commemorate the journey. Although the Solitaire is the only extinct bird to have a former constellation named for it, celestial mapmakers did not know what it looked like and star maps depict other birds.

Some later scholars doubted Leguat's story, and the Solitaire's existence. In 1789, subfossil Solitaire bones encrusted in stalagmite were discovered in a cave and sent to Georges Cuvier about 1830. For unknown reasons he stated they had recently been found on Mauritus (which caused confusion), until they were compared with other bones from Rodrigues (that were found to belong to the same species). Subfossils were also recovered during the 1860s, but more complete remains were found during the 1874 transit of Venus (since an observation station was located on the island). Many of these excavations were requested by brothers Alfred and Edward Newton, who used them to describe the osteology of the bird in detail. Thousands of bones were excavated, and mounted skeletons were composed from the remains of several specimens. It has been suggested that the skeleton of this species is the best described after that of humans. These finds confirmed Leguat's descriptions, but at this time no living residents of Rodrigues remembered having seen specimens. In 1831, a man who had lived on Rodrigues for 40 years stated he had never seen birds large enough to be Solitaires. Rodrigues covers only 104 square kilometres (40 sq mi), making it implausible that the bird would have survived undetected.

See also

• Holocene extinction
• List of extinct birds

References

Footnotes

Sources