The Rodrigues solitaire (Pezophaps solitaria) is an extinct flightless bird that was endemic to the island of Rodrigues, east of Madagascar in the Indian Ocean. A member of the family of pigeons and doves, it was most closely related to the also extinct dodo of the nearby island Mauritius, the two forming the subfamily Raphinae. The Nicobar pigeon is their closest living genetic relative.
Rodrigues solitaires grew to the size of swans, and demonstrated pronounced sexual dimorphism. Males were much larger than females and measured up to in height and in weight, contrasting with and 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. Gizzard stones helped digest its food, which included fruit and seeds. Both sexes were highly territorial, with large bony knobs on their wings that were used in combat, probably due to competition for the limited resources on the island. The Rodrigues solitaire laid a single egg that was incubated in turn by both sexes.
First mentioned during the 17th century, the Rodrigues solitaire was described in detail by François Leguat, the 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 18th century. 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 1786. Thousands of bones have subsequently been excavated. It is the only extinct bird with a former constellation named after it, Turdus Solitarius.
Taxonomy
The French explorer 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 1689 tract by his sponsor Marquis Henri Duquesne, which used the name "solitaire" in reference to the Réunion ibis. The bird was first scientifically named in 1789 as a species of dodo (Didus solitarius, based on Leguat's description) by the German naturalist Johann Friedrich Gmelin in the thirteenth edition of Systema Naturae. In 1786, subfossil Rodrigues solitaire bones encrusted in stalagmite were discovered in a cave on Rodrigues and sent to the French naturalist Georges Cuvier in about 1830. For unknown reasons, he stated they had recently been found on Mauritius, which caused confusion, until they were compared with other bones found on Rodrigues in 1831 that were shown to belong to the same, distinct species by the English naturalists Hugh Edwin Strickland and Alexander Gordon Melville in 1848.
Strickland and Melville suggested the common descent of the Rodrigues solitaire and the dodo in their 1848 monograph about the latter. They dissected the only known dodo specimen with soft tissue, comparing it with the few Rodrigues solitaire remains then available. They stated that, although not identical, these birds shared many distinguishing features in the leg bones otherwise only known in pigeons. The fact that the Rodrigues solitaire laid only one egg, fed on fruits, was monogamous and cared for its nestlings also supported this relationship. Strickland recognised its generic distinction and named the new genus Pezophaps, from ancient Greek ' ( 'pedestrian') and ' ( 'pigeon'). The differences between the sexes of the bird were so large that Strickland thought they belonged to two species, naming the smaller female bird Pezophaps minor in 1852.
Additional subfossils were 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. Study of skeletal features by the Newtons indicated that the solitaire was morphologically intermediate between the dodo and ordinary pigeons, but differed from them in its unique carpal knob. An atypical 17th-century description of a dodo and bones found on Rodrigues, now known to have belonged to the Rodrigues solitaire, led the British taxidermist Abraham Dee Bartlett to name a new species in 1851, Didus nazarenus; it is now a junior synonym of this species.
At one point it was suggested that the skeleton of this species is the best described after that of humans. In spite of the evidence, some later scholars doubted Leguat's story, and the existence of the Rodrigues solitaire. In 1921, the American linguist Geoffroy Atkinson claimed Leguat's memoir was merely a novel, and that the man had never even existed, and in 1955, the British ecologist George Evelyn Hutchinson doubted aspects of the bird's biology mentioned by Leguat. Today, it is widely accepted that Leguat's memoirs are credible observations of the bird in life.
For many years the dodo and the Rodrigues solitaire were placed in a family of their own, the Raphidae (formerly Dididae), because their exact relationships with other pigeons were unresolved. Each was also placed in a monotypic family (Raphidae and Pezophapidae, respectively), as it was thought that they had evolved their similarities independently. Osteological and DNA analysis has since led to the dissolution of the family Raphidae, and the dodo and solitaire are now placed in the columbid subfamily Raphinae and tribe Raphini, along with their closest relatives. In 2024, the new subtribe Raphina was created to include only the dodo and the solitaire.
Evolution
In 2002, American geneticist Beth Shapiro and colleagues analysed the DNA of the dodo and the Rodrigues solitaire for the first time. 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. The genetic evidence was interpreted as showing the Southeast Asian Nicobar pigeon (Caloenas nicobarica) to be their closest living relative, followed by the crowned pigeons (Goura) of New Guinea, and the superficially dodo-like tooth-billed pigeon (Didunculus strigirostris) from Samoa. This clade consists of generally ground-dwelling island endemic pigeons. The following cladogram shows the closest relationships of the dodo and the Rodrigues solitaire within Columbidae, based on Shapiro et al., 2002:
thumb|A [[Nicobar pigeon, the closest living relative of the Rodrigues solitaire and the dodo according to DNA studies]]
A similar cladogram was published in 2007, inverting the placement of Goura and Didunculus and including the pheasant pigeon (Otidiphaps nobilis) and the thick-billed ground pigeon (Trugon terrestris) at the base of the clade. Based on behavioural and morphological evidence, Jolyon C. Parish proposed that the dodo and Rodrigues solitaire should be placed in the Gourinae subfamily along with the Goura pigeons and others, in agreement with the genetic evidence
The 2002 study indicated that the ancestors of the Rodrigues solitaire and the dodo diverged around the Paleogene–Neogene boundary. The Mascarene Islands (Mauritius, Réunion, and Rodrigues), are of volcanic origin and are less than 10 million years old. Therefore, the ancestors of both birds probably remained capable of flight for a considerable time after the separation of their lineage. The Nicobar and spotted green pigeon were placed at the base of a lineage leading to the Raphinae, which indicates the flightless raphines had ancestors that were able to fly, were semi-terrestrial, and inhabited islands. This in turn supports the hypothesis that the ancestors of those birds reached the Mascarene islands by island hopping from South Asia. The dodo lost the ability to fly owing to the lack of mammalian predators on Mauritius. Another large, flightless pigeon, the Viti Levu giant pigeon (Natunaornis gigoura), was described in 2001 from subfossil material from Fiji. It was only slightly smaller than the Rodrigues solitaire and the dodo, and it too is thought to have been related to the crowned pigeons.
Description
thumb|left|upright|alt=Illustration of a light-brown solitaire with a large black knob on the base of the beak|Restoration by [[Frederick William Frohawk, 1907]]
The beak of the Rodrigues solitaire was slightly hooked, and its neck and legs were long. One observer described it as the size of a swan. The skull was long, flattened at the top with the fore and hind parts elevated into two bony ridges structured with cancellous bone. A black band (a contemporary description described it as a "frontlet") appeared on its head just behind the base of the beak. The plumage of the Rodrigues solitaire was described as grey and brown. Females were paler than males and had elevations on the lower neck. Males were considerably larger than females, measuring in height and weighing up to , whereas females were and weighed up to . This is only 60% of the weight of a mature male. He described its appearance as follows: