Dodos and solitaires

(Raphidae)

Class Aves

Order Columbiformes

Family Raphidae

Thumbnail description
Large, stocky, flightless birds

Size
40 in (100 cm); 24–40 lb (10.5–17.5 kg); some estimates up to 50 lb (22.5 kg)

Number of genera, species
2 genera; 3 species

Habitat
Woodlands

Conservation status
Extinct

Distribution
Mascarene Islands

Evolution and systematics

The Mauritius dodo (Raphus cucullatus), Rodrigues solitaire (Pezophaps solitaria), and the Réunion solitaire (Raphus soliatrius) were three very large, flightless birds usually treated taxonomically as constituting the family Raphidae within the order Columbiformes. In their isolation on the Mascarene Islands, 500 mi (800 km) east of Madagascar, these aberrant pigeons evolved gigantism and flightlessness in the absence of native ground predators. Their existence has been documented in journal accounts and, in the case of the dodo and Rodrigues solitaire, in illustrations made by eyewitnesses as well as from skeletal material that has been excavated and examined in detail.

Masauji Hachisuka, in his extensive monograph on these species, reports about 20 firsthand accounts that mention the dodo, and evidence exists of 16 live dodos that were exported to Europe, India, or Japan. The dodo first appeared in the journals of Dutch Admiral Jacob Cornelius Van Neck in 1598 (published in 1601), who described dodos (in translation) as "larger than the swan, having the body of an ostrich, the feet of an eagle, few feathers on the body, the wings like a teal's." Among the more extensive accounts of the dodo, and perhaps also the last report of this species in the wild, is that of Volquard Iversen, who was shipwrecked on Mauritius for five days in 1662. Skeletal remains of dodos have been found in alluvial outwashes in bogs on the island. One mounted specimen reached Europe and was mentioned in a 1656 publication, but this specimen was burned in 1755 and only its head and right foot were saved. The left foot of another individual exists in the British Museum and another head in the Zoological Museum of Copenhagen.

More is known of the Rodrigues solitaire. The journal of François Leguat describes this species' behavior in a rather extensive account written when he and eight others inhabited Rodrigues for two years, from April 3, 1691 until May 21,1693. Specimen records of solitaires are more extensive than those of dodos; over 2,000 solitaire bones were found in caves on the island between 1864 and 1875.

The existence on Réunion of another species of solitaire has been inferred only from contradictory travelers' accounts; no illustrations exist of this bird, nor have any raphid skeletal remains been found. This "solitaire" may actually have been an ibis (genus Threskiornis), as arguments attempt to reconcile skeletal remains found in the 1990s with the meager description of Réunion's "solitaire" by Sieur DuBois in 1669. This Réunion bird was described as a solitary bird, rarely seen, that inhabited remote mountain forests, fed on worms and soil insects, flew "but very little," and had a bill "like that of a Woodcock but larger." Nothing is known of its breeding. It was considered frequent in 1705 but disappeared suddenly thereafter and was last reported being seen in 1708.

While, at first glance, the Raphidae appear unlike pigeons, they are actually very close to them anatomically. Hence, both the pigeons (Columbidae) and the Raphidae are placed in the order Columbiformes. The dodo's big hooked bill is fore-shadowed by the enlarged bill tips seen in most pigeons, and the skeletons of the dodos and pigeons are similar given the

dodo's adaptation to flightlessness. Dodo feathers were identical to pigeon feathers and the loose plumage is like that seen in young squab. In fact, it is now generally agreed that the dodos are an example of neotony or paedomorphosis—the retention of juvenile characters into adulthood. Derived from pigeon-like stock, the dodos lost their wings, developed gigantism, and retained juvenal plumage and body form.

Physical characteristics

These birds were all about the size of a turkey, were heavily built, and possessed much reduced wings, strong feet, and a strong bill. The dodo had a featherless face, and its plumage was represented as bluish or brownish gray in paintings. Its bill was heavy and hooked and bore transverse ridges; possibly the bill's rhampotheca (horny sheath) was molted seasonally. Compared with the dodo, the Rodrigues solitaire was taller and more slender, with a smaller head and a slighter bill, metacarpal wing spurs, and largely brownish plumage.

John Tenniel's illustrations of the dodo in Lewis Carroll's Alice's Adventures in Wonderland express the traditional image of a dodo: a fat bird with a clumsy shape, a very large head, a heavy hooked bill, and a little tail of curly feathers. This characterization of the dodo may not be accurate. In 1993, Andrew Kitchener presented several arguments for a thinner dodo. He noted that drawings made before 1620 (by individuals who had seen these birds on the islands) showed thinner birds than did illustrations made after 1620 (which were done mostly in Europe). The very fat birds depicted in illustrations likely represent individual captives in Europe. Traditional descriptions of size emphasize Thomas Herbert's estimate (in 1634) of dodo body mass at 50 lb (22.7 kg), but estimates of body mass based on scale models, skeletal mass, and various scaling relationships show the dodo as a normally "thin" bird (about 23–39 lb; 10.5–17.5 kg). Scaling relationships suggest that the Rodrigues solitaire may not have been as large as Leguat's estimate (in 1708) of a body mass of 45 lb (20.4 kg).

Distribution

Extinct, known only from Mauritius, Rodrigues, and possibly Réunion islands in the Indian Ocean

Habitat

Woodlands; no journal account associates either species with shore or river banks

Behavior

Despite the attention the birds received as curiosities by early seventeenth century visitors, nothing was recorded of the dodo's habits. The habits of the Rodrigues solitaire were better documented by Leguat and another later, brief account. Rodrigues solitaires, at least, were territorial. They produced wing sounds in apparent courtship displays and made use of wing spurs in agonistic encounters.

Feeding ecology and diet

The dodo diet was described as fruit and that of the Rodrigues solitaire as seeds, fruit, and foliage. Gizzard stones have been found in association with skeletal remains of both species. A marked annual fat cycle, common for many Mascarene species, has been postulated for the dodo. Such a cycle had been reported by Legaut for the Rodrigues solitaire: fat from March to September and thin the remainder of the year.

Stanley Temple postulated a close mutualistic relationship between the dodo and the tambalacoque tree (Sideroxylon grandiflorum; also known as Calvaria major) in that germination of the tree's hard seeds was promoted (or assisted) by passage through the dodo's gut. However, evidence for this relationship is tenuous.

Reproductive biology

There is very little information of undisputed acceptance. These species probably laid clutches of a single egg in nests on the ground. Young were probably altricial (hatched helpless and requiring considerable care), but no information exists to describe either their appearance or development. Leguat described Rodrigues solitaire adults bringing young together to a vacant territory as an arranged "marriage," but this behavior may represent formation of creches of young.

Conservation status

Extinct; dodo by 1670, Rodrigues solitaire by 1770, Réunion solitaire by 1750. Primary cause of extinction attributed to predation on eggs and young by pigs (Sus scrofa), rats (Rattus rattus and R. norvegicus), and, on Mauritius, monkeys (Macaca fascicularis). Cats (Felis catus) may have also have played a role. Introduced herbivores—cattle (Bos taurus), goats (Capra spp.), and, on Mauritius, deer (Cervus timorensis—likely altered native habitat, but this impact on dodo and solitaire populations was probably not as severe as that caused by predation by pigs, rats, and monkeys. Early extinctions of other native species on the Mascarene Islands are also attributed to introductions of exotic species.

Significance to humans

Dodos and solitaires were killed for food and to restock supplies of ships visiting the islands. While still extant, these species were presented to Europe as curiosities of exotic islands. The very short time between their European discovery and their extinction has enhanced their cultural significance as symbols of extinction.

Species accounts

List of Species

Dodo

Raphus cucullatus

taxonomy

Struthio cucullatus Linne, 1758, Mauritius (the name Didus ineptus Linne, 1766, used in older literature).

other common names

French: Dronte de Mourice; German: Dronte; Spanish: Dronte de Mauricio.

physical characteristics

Large turkey-like bird. Contemporary paintings of this species, based on live birds or traveler's descriptions, show grayish plumage, darker above and lighter below, yellowish white wings with five to six larger feathers, and a tail with five curled feathers. The hooked bill was deep yellow with a horny sheath on the upper and lower mandibles. The skin on the face and around the bill was dull gray and bare of feathers.

distribution

Mauritius, a small (720 mi²; 1,865 km²) volcanic island about 500 mi (800 km) east of Madagascar in the Indian Ocean.

habitat

Woodlands.

behavior

The most extensive record of the dodo comes from Volquard Iversen, who was shipwrecked on Mauritius for five days in 1662 (not in 1669 as indicated in some accounts). Iversen did not find the dodo on the mainland but did see it on an islet that was isolated from pigs and monkeys but that was still accessible by foot at low tide. Iversen wrote: "Amongst other birds were those that men in the Indies call doddaerssen; they were larger than geese but not able to fly. Instead of wings they had small flaps; but they could run very fast." He wrote that after catching them, other dodos would run up when the captive screamed ("When we held one by the leg he let out a cry, others came running forward to help the prisoner, and were themselves caught"). One Dutch sailor described dodos in 1631 as "very serene or majestic, they showed themselves to us with an extremely dark face with open beak, very dapper and bold in their walk, would hardly move out of our way."

feeding ecology and diet

Dodos reportedly ate fruit. Dodos swallowed stones apparently to aid the breakdown of food in the crop. This species apparently had a seasonal fat cycle. A possible mutualistic relationship existed between dodos and the tambalacoque tree, with passage of the tree's seed through the dodo's gut promoting the seed's germination.

reproductive biology

Dodos nested on the ground and laid a one-egg clutch. The egg was described by François Cauche in 1651 as being the same size as a half-penny roll. Cauche used this same comparison for the egg of the great white pelican (Pelecanus onocrotalus), which has a 6.3 oz (180 g) egg. The general relationship between egg mass and incubation period suggests that the dodo's incubation period was about 37 days.

conservation status

Extinct. The Mascarene Islands had been known to Arab navigators prior to European contact but nothing of their exploration of these islands is known other than the appearance of the islands on their maps. For Europeans, the existence of Mauritius was first recorded in 1507 by Portugese sailors, and until 1598 it remained uninhabited except for pigs, goats, and fowl that were stocked on the island. The primary cause of extinction of the dodo is likely to have been egg predation by introduced pigs, monkeys, and cats, even though dodos were slaughtered in large numbers by sailors. Dodos were very rare by 1640, although some survived to 1662, at least, on offshore islets. The last sighting of a dodo was recorded somewhere between 1665 and 1670, but it is an unconfirmed report.

significance to humans

Dodos were a source of fresh meat for crews and passengers of ships traveling in the Indian Ocean. The dodo is the first species to be counted as becoming extinct because of human activity.

Rodrigues solitaire

Pezophaps solitaria

taxonomy

Didus solitaria Gmelin, 1789, Rodrigues.

other common names

French: Dronte de Rodriguez; German: Einsiedler; Spanish: Solitario de la Rodríguez.

physical characteristics

These large birds were strongly sexually dimorphic in size; males were larger than females and possessed metacarpal spurs the size of "musketballs."

distribution

Rodrigues, a small (40 mi²; 104 km²) volcanic island about 220 mi (350 km) east of Mauritius in the Indian Ocean.

habitat

Woodlands.

behavior

Better known than the dodo from contemporary accounts. François Leguat described their behavior in 1692: solitaires lived in pairs, were territorial, laid clutches of a single egg, and their young joined a creche. Skeletal remains show mended fractures in the metacarpus that suggest a pugilistic function. Wings were vigorously flapped "when angry" and produced "a great noise…something like thunder in the distance" or "very like that of a rattle;" this display was likely an aspect of courtship behavior. Their voice had been described as similar to that of a gosling's squeak.

This solitaire was an apparently territorial species. During incubation or while caring for their young during the time "which [it] is not able to provide for its self in several Months, they will not suffer any other Bird of their Species to come within two hundred yards round of the Place;" males responded to intruding males and females to other females. This stated measure suggests maintenance of a 25-acre (10-ha) territory.

feeding ecology and diet

This solitaire was reported to have fed on seeds, Latania palm fruit, and foliage. Like dodos, Rodrigues solitaires appeared to

have had a marked annual fat cycle in which they were fat from March to September and thin for the remainder of the year. Gennes de la Chancelière described two young birds as each having a fat layer 1-in (2.5-cm) thick over the body. Gizzard stones have been found with skeletal remains.

reproductive biology

Rodrigues solitaires laid a single egg in a nest constructed of palm leaves. Nests were built on the ground and were about 16 in (40 cm) in height. Both sexes incubated eggs. Leguat reported a seven-week incubation period, but based on estimated egg size, models predict a 37-day incubation period. Young apparently joined creches after a period with parents, although Leguat described this social amalgamation of broods as "marriages."

conservation status

Extinct. Portuguese sailors reached Rodrigues in 1507, but the island was not inhabited by humans until May 1, 1691, when Leguat and eight others arrived. Introduced pigs were especially devastating predators of young solitaires and eggs. A few solitaires were reported in the wild in 1755 and 1761, but these seem to be the last sightings. Individuals who speculate that the solitaire disappeared in the 1750s blame feral cats and possibly dry season fires for the solitaire's demise.

significance to humans

Rodrigues solitaires were a source of fresh meat for crews and passengers of ships traveling in the Indian Ocean.

Resources

Books

Cheke, A.S. "An Ecological History of the Mascarene Islands, with Particular Reference to Extinctions and Introductions of Land Vertebrates." In Studies of Mascarene Island Birds, edited by A.W. Diamond. Cambridge: Cambridge University Press, 1987.

Hachisuka, M. The Dodo and Kindred Birds, or the Extinct Birds of the Mascarene Islands. London: Witherby, 1953.

Quammen, D. The Song of the Dodo: Island Biogeography in an Age of Extinctions. New York: Scribner, 1996.

Strickland, H.E., and A.G. Melville. The Dodo and Its Kindred. London: Reeve, Benham and Reeve, 1848.

Periodicals

Brom, T.G., and T.G. Prins. "Microscopic Investigation of Feather Remains from the Head of the Oxford Dodo, Raphus cucullatus." Journal of Zoology (London) 218 (1989): 233–246.

Kitchener, A.C. "On the External Appearance of the Dodo, Raphus cucullatus (L., 1758)." Archives of Natural History 20 (1993): 279–301.

Livezey, B.C. "An Ecomorphological Review of the Dodo (Raphus cucullatus) and Solitaire (Pezophaps solitaria), Flightless Columbiformes of the Mascarene Islands." Journal of Zoology (London) 230 (1993): 247–292.

Mourer-Chauviré, C., R. Bour, and S. Ribes. "Was the Solitaire of Réunion an Ibis?" Nature 373 (1995): 568.

Owadally, A.W. "The Dodo and the Tambalacoque Tree." Science 203 (1979): 1363–1364.

Temple, S.A. "Plant-Animal Mutualism: Coevolution with Dodo Leads to Near Extinction of Plant." Science 197 (1977): 885–886.

Peter E. Lowther, PhD