Tongatapu rail

The only specimen is now lost

Quite a few bird species of the past were described from only a single specimen that is now lost. One of them is the Tongatapu rail. Of this rail species (family Rallidae), historical reports and descriptions have survived that are based on observations and collecting during the voyages of the English seafarer James Cook in the 18th century.

When Cook and his expedition ships reached the island of Tongatapu in the Kingdom of Tonga in the South Pacific in June 1777, William Anderson, a Scottish naturalist and surgeon, recorded a variety of birds that were collected by locals and sold to the seafarers. These included pigeons, small rails, and purple swamphens.

During this third voyage, the German naturalists Reinhold and Georg Forster also encountered a specimen of the Tongatapu rail on the main island of the Tonga archipelago. The well-known English naturalist and President of the Royal Society, Joseph Banks, acquired the bird skin, which was presumably preserved in alcohol. This specimen was the only one documented in scientific collections. It was mentioned in the Solander catalogue as part of the Banks collection and described in manuscript list 3 as Rallus spectabilis. Unfortunately, this specimen is now lost.

It is speculated that the specimen may have been among those that Joseph Banks distributed in 1792 between important institutions such as the British Museum and the British surgeon and naturalist John Hunter. Banks aimed to make his extensive natural-history collection accessible to the scientific community even after his death, to ensure that specimens were preserved and could serve research. However, the limited possibilities for documentation and preservation at the time, as well as the challenges of handling delicate natural-history preparations, likely meant that some specimens were lost over time.

On the third South Seas voyage, Cook and his crew also discovered the now extinct Kiritimati sandpiper. The only known specimen of this bird species, which also became part of Joseph Banks’s collection, is now lost as well.

The scientific descriptions and catalogue entries prepared by Banks and his colleagues are the only physical evidence for the Tongatapu rail’s existence today. However, there is also a contemporary painting by Georg Forster, created during Cook’s second South Seas voyage between 1772 and 1775, which has often been assumed to depict the lost Tongatapu rail. This assumption does not fit with the fact that the Tongatapu rail was only discovered in 1777. Some experts therefore suspect that Forster actually depicted Hypotaenidia (Gallirallus) philippensis ecaudatus, a subspecies of the buff-banded rail. This illustration may not have been made on the island of Tongatapu, but on the smaller island of Nomuka, which also belongs to the Polynesian island nation of Tonga.

Tongatapu rail – fact sheet

scientific names	Hypotaenidia hypoleucus, Gallirallus hypoleucus, Rallus hypoleucus, (Rallus spectabilis)
original range	Tongatapu (South Pacific)
time of extinction	no earlier than 1777
causes of extinction	habitat loss, introduced animals on islands, hunting

Was James Cook responsible for the extinction of the Tongatapu rail?

James Cook and his crew may have contributed indirectly to the extinction of the Tongatapu rail, especially by introducing dogs to the Tonga Islands in October 1773. In his journal, Cook documented that he left dogs on Tongatapu and Nomuka: “I also left a young dog and a bitch; animals which they do not have and which they like very much.”

William Anderson, who accompanied Cook on his third South Seas voyage, reported five years later that he found a considerable number of feral dogs on Tongatapu. Dogs are well-known and effective predators that hunt eggs, juveniles, and adult birds—especially birds that can fly poorly or not at all. British ornithologist Julian P. Hume writes in Extinct Birds (2017) that the Tongatapu rail, “like so many island rails, could at best fly only a little”. This means that the introduced dogs could have caused a substantial population decline in the ground-nesting Tongatapu rail.

It would certainly be unreasonable to hold Cook’s expeditions responsible for the Tongatapu rail’s extinction, but it is likely that the introduction of dogs by Cook and his men had a negative impact on the Tongatapu rail population.

Possible reasons for the extinction of the Tongatapu rail

While Cook and his crew undoubtedly affected the ecosystems of the Tonga Islands, it is unlikely that they alone were responsible for the Tongatapu rail’s extinction. The decline of this species was probably the result of a combination of several factors:

Introduction of non-native species: pigs, rats, and cats

In addition to the dogs introduced by Cook, other predatory animal species such as pigs and rats reached the Tonga Islands long before his arrival via Polynesian settlers. Pigs, which are omnivores, pose a significant threat to ground-nesting birds, because they root through the ground for food, plunder nests, and eat eggs and young birds. In a study published in 1990, Linda W. Cuddihy and Charles P. Stone showed that pigs can alter ecosystem structure and contribute to the eradication of various native species. These changes affect both animals and plants, since pigs uproot vegetation and disturb the soil.

Rats, which were generally introduced to islands unintentionally, have also led to the decline and extinction of many island bird species, especially ground-nesting species. Cats, too, which arrived in the Tonga archipelago via European explorers, have spread across almost all Tonga islands. Feral domestic cats are known as versatile predators and eat eggs, chicks, and adult birds, as well as amphibians and reptiles.

The combination of introducing dogs, pigs, rats, and cats likely led—through predation and habitat destruction—to a sharp decline and ultimately to the extinction of the Tongatapu rail. These predators shifted the balance of the island ecosystem and put particular pressure on ground-nesting birds such as the rail.

A similar fate befell the Tonga skink, which was endemic to Tongatapu and disappeared at the beginning of the 19th century. It is assumed that predation by introduced predators and the loss of its natural habitat were the main causes of its extinction.

Habitat changes: deforestation and agriculture

Before human settlement, the Tonga Islands were densely forested and provided a variety of habitats, especially for ground-nesting species such as the Tongatapu rail. These lush forests were crucial for the survival of native species. With the arrival of Polynesian settlers around 2,800 years ago, however, large-scale clearing of forests began to make room for cultivating crops such as taro, yams, and bananas. This deforestation led to forest fragmentation and the destruction of important habitats for the native fauna.

When Cook reached the island of Tongatapu in the late 18th century, he noted that most of the island was already used for agriculture and covered with plantations. In a 1993 study on the birds of Tonga before and after human settlement, the American paleozoologist David W. Steadman aptly summarized the situation:

“The arrival of humans has had a stronger impact on the avifauna of Tonga than any climatic, tectonic, or biological event of the last roughly 100,000 years.”

Biogeography of Tongan Birds Before and After Human Impact. PNAS 1993. D. W. Steadman.

The arrival of Europeans in the Kingdom of Tonga intensified these changes through the introduction of new agricultural practices, the cultivation of monocultures, and the growing of commercial crops such as sugarcane and coconut palms. The associated destruction of forests likely led to the loss of feeding and breeding sites for the Tongatapu rail. As a ground-nesting bird, this species depended on dense vegetation to build its nests and protect its young from predators. Steadman emphasizes that the loss of forest habitats was one of the main reasons for the extinction of many Polynesian bird species, including rails.

Trade and collecting of live birds

Hunting and other human disturbance undoubtedly played a key role in the decline and eventual extinction of the Tongatapu rail. On isolated Pacific islands, where animals often have no natural enemies and show little fear of humans (island tameness), ground-nesting, weak-flying birds such as the Tongatapu rail are particularly vulnerable to anthropogenic influences and hunting.

Since their arrival in the Tonga archipelago, Polynesian settlers hunted native birds as a food source. This practice continued for centuries and likely led to a continuous decline in rail populations. The visits of James Cook and other European explorers further increased hunting pressure, as they brought new technologies and methods that improved hunting efficiency. In his journals, Cook mentioned that his crew hunted various birds during their stays on the Tonga Islands, including rails.

In addition, trading live birds was a common practice among Tongans, especially during visits by European ships. Locals often brought rare bird species to the ships for sale. This trade may have significantly contributed to decimating Tongatapu rail populations, as many birds were captured and removed from their natural habitat. It is documented that Tongans regularly offered birds for sale to Cook and his men, further increasing pressure on already vulnerable populations.

When did the Tongatapu rail go extinct?

After the discovery of the Tongatapu rail in 1777, no further specimen of this bird species was seen, so no exact extinction date is documented. Most experts—including the New Zealand ornithologist David G. Medway in The Tongatapu Rail Gallirallus hypoleucus – an Extinct Species Resurrected? (2010)—assume that the species went extinct by the end of the 18th century at the latest.

According to Medway, the island of Tongatapu was already an unfavorable habitat for rails in the 1770s—especially if they were nearly flightless. By that time, the island had already been inhabited by humans for almost 3,000 years, and much of the original forests had been cleared, as Steadman writes in Extinction & Biogeography of Tropical Pacific Birds (2006).

Steadman, Medway, and Hume consider it somewhat surprising that the Tongatapu rail survived at all into the 1770s. For centuries, the bird had to withstand hunting by locals, the destruction of its habitat, and pressure from introduced mammals. The dogs introduced by Cook were probably only the final decisive factor that led to the species’ ultimate extinction.

Tongatapu rail: discovered in 1777, recognized as a distinct species in 1867

English ornithologist John Latham had access to the animal specimens collected by Joseph Banks on James Cook’s South Seas voyages. The Tongatapu rail specimen served Latham in 1784 as the basis for his detailed description of the bird. He emphasized the distinctive plumage features that set this bird apart from other rail species:

“The head of this variety is paler, and the stripe above the eye gray; the back of the neck is barred brown and white; the middle of the back and the scapulars are white, with very little brown mixed with the former; the wing-coverts are olive-brown, barred with white; (…) the tail is (…) olive-brown and white barred: all the underparts are white: bill and legs are pale yellowish-brown. Inhabits Tongatapu. In the collection of Sir Joseph Banks.”

A General Synopsis of Birds. 1790-1801. J. Latham

At that time, the rail from the island of Tongatapu still had no specific name. Latham and the German naturalist Johann Friedrich Gmelin regarded the species as a variety of the buff-banded rail (Hypotaenidia philippensis), a widespread rail species found in many parts of the Pacific. Scottish ornithologist Robert Gray, by contrast, suspected around 1850 that the bird from Tongatapu was a variant of Lewin’s rail (Rallus pectoralis).

It was not until 1867 that naturalist Otto Finsch and ornithologist Gustav Hartlaub contradicted these views and recognized the Tongatapu rail as a distinct species, giving it the scientific name Rallus hypoleucus:

“Although, apart from Latham’s, no further reports on this remarkable rail exist, and it may therefore appear somewhat doubtful, we cannot—given the complete difference in coloration—bring ourselves to declare it, with Gray, a variety of R. pectoralis. With our very limited knowledge of the ornithology of the Tonga Islands, (…) and in view of the secretive way of life of these birds, it seems to us by no means unlikely that this characteristic rail might not be rediscovered. We therefore have no hesitation in recognizing it as a species and naming it specifically.”

Contribution to the fauna of Central Polynesia. Ornithology of the Viti, Samoa and Tonga Islands. 1867. pp. 163–164. O. Finsch & G. Hartlaub.

Confusions among rails

In the 19th century—and even in the early 20th century—the Tongatapu rail was often confused with other rail species or treated as a synonym of them. British ornithologist Richard Bowdler Sharpe listed Rallus hypoleucus, despite the original description by Finsch and Hartlaub, as a synonym of Hypotaenidia philippensis in the Catalogue of the birds in the British Museum (1894). This decision was probably based on morphological similarities and insufficient information about the actual differences between the species.

The Australian ornithologist Gregory Mathews, who worked extensively on the classification of Australian and Oceanian birds, also treated the Tongatapu rail as a synonym of Rallus forsteri, now known as the buff-banded rail subspecies Gallirallus philippensis ecaudatus.

The confusion among rail species can likely be attributed to several factors. The birds often share similar body shapes and plumage features, making them difficult to distinguish. In addition, at the time of these classifications researchers often had only a few specimens available, and information on variability within and between species was limited. Furthermore, descriptions and illustrations from the 18th and 19th centuries were not always precise, so differences between species may have been overlooked or misinterpreted.

Because of these confusions, the Tongatapu rail was not recognized as a distinct species for a long time, which resulted in an underestimation of biodiversity on the Tonga Islands. Lumping different species under one name also led to the loss of valuable information about the Tongatapu rail’s specific ecology and distribution. Only in 1867 did Finsch and Hartlaub recognize differences in the coloration and morphology of the Tongatapu rail and describe it as a valid, distinct species.

The Tongatapu rail in the Baillon Collection?

The Musée George Sand et de la Vallée Noire in La Châtre, France, houses the Baillon Collection, which comprises 2,480 prepared specimens of 1,318 bird species collected by Emmanuel Baillon and his son François Baillon. A 2014 study by Christophe Gouraud deals with 62 partly unidentified bird specimens from the collection that date from the 18th century.

Among these specimens collected before 1800 is an item with inventory number MLC.2011.0.1170, catalogued as an unidentified rail (Rallidae indet.). This specimen comes from the Tonga Islands—more precisely from the main island of Tongatapu—and was handed over to the Baillon Collection by the naturalist Georges Cuvier in 1821. Unfortunately, the specimen is in poor condition, which makes reliable identification much more difficult. Because of these preservation problems, it is hard to determine whether this specimen is the lost Tongatapu rail.

Although there are no direct indications that bird specimens from James Cook’s voyages entered the Baillon Collection directly, the possibility remains that such specimens could have reached it indirectly. Specimens originally collected by Joseph Banks and passed on to other institutions may later have entered private collections like Baillon’s through sales, exchanges, or auctions.

The path of natural-history objects is often complex and winding, especially in an era when scientific collections were still being established and frequently changed hands. In the Baillon Collection, around 400 specimens have either lost their labels or their wooden bases, meaning crucial information about their provenance has been irretrievably lost. To determine conclusively whether the Tongatapu rail is in Baillon’s collection, comprehensive research into the provenance and history of the specimens there would be necessary.