Tristan thrush

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Tristan thrush
Tristan Thrush on Nightingale island.jpg
On Nightingale Island
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Family: Turdidae
Genus: Turdus
Species:
T. eremita
Binomial name
Turdus eremita
(Gould, 1855)
Synonyms [1]
  • Nesocichla eremitaGould, 1855

The Tristan thrush (Turdus eremita), also known as the starchy, [2] is a species of bird in the thrush family that is endemic to the British overseas territories of the isolated Tristan da Cunha archipelago in the South Atlantic Ocean.

Contents

Description

The bird was described by John Gould as being similar in size and appearance to the song thrush, and by Henry Moseley as like a very dark-coloured song thrush. [2] However, it also has the short rounded wings and reduced keel indicative of a reduced need for flight, typical of bird species adapted to life on small islands. [3]

This thrush typically has a length of about 22 cm (8.7 in). [4] The nominate subspecies from Tristan differs from that from Nightingale Island, with the Tristan birds being warm dark brown on the upperparts rather than dull sooty-brown, rufous rather than dark fuscous on the sides of the head, and rufous-brown, rather than brownish-black, on the underparts. Birds from Inaccessible Island appear to be intermediate, with the sides of the head of a specimen from there speckled both rufous and fuscous. [5]

Distribution and habitat

The thrush is found on Tristan, Inaccessible, Nightingale, Middle and Stoltenhoff Islands in the Tristan group. It uses all the natural habitats available on the islands, including rocky shorelines, tussock grassland, fern-dominated shrubland and wet heathland. [6]

Taxonomy

The thrush is thought to have evolved from an ancestor in the genus Turdus from South America, and resembles an immature austral thrush, but its adaptations to life on a small island group, including an unusual brush-tipped tongue modified for extracting the contents of eggs, have been used as reasons to warrant its separation into the monotypic genus Nesocichla. [7] However, molecular analysis has indicated that not only is it part of a South American clade of Turdus, but also that it falls squarely within that genus. [3]

There are three subspecies, the ranges of which correspond to the three main islands in the group: [6] [7]

Behaviour

Breeding

The thrush breeds from September to February. Its cup-shaped nest is woven from strands of grasses and other vegetation, and sited on or close to the ground. It lays a clutch of two or three, occasionally four, eggs. The fledging period is about 20 days. [6]

Feeding

Scavenging on dead bird on Nightingale Island Nesocichla eremita -Nightingale Island -eating-8.jpg
Scavenging on dead bird on Nightingale Island

An opportunistic omnivore and scavenger, the thrush feeds on earthworms and other invertebrates of the soil and leaf litter, as well as on carrion, berries, [2] the eggs and fledglings of other birds, and kitchen scraps. [6]

Bird predation

In 2010 a paper published by Peter Ryan and Rob Ronconi in the journal Ardea reported an observation of Tristan thrushes breaking open an egg of the Atlantic yellow-nosed albatross. They also found that the thrush is a regular predator of the eggs and small chicks of the great shearwater, being responsible for almost half of the egg losses by that species during the early incubation period in a colony on Inaccessible Island. [8] They saw evidence that the thrushes remove eggs of the spectacled petrel (a breeding endemic of Inaccessible Island) from their nesting burrows. The thrushes are also known to kill both white-bellied and white-faced storm petrels directly, probably by taking them from their burrows. [8] [9] Furthermore, they have been observed to drink blood from penguins. [10] The thrushes will also prey on the chicks, and occasionally the adults, of the Inaccessible Island rail. [11] With the exception of seabirds such as the brown skua and rare vagrant raptors, the Tristan thrush is the largest terrestrial predator on Tristan da Cunha, occupying a unique position in its ecosystem for a songbird.

Status and conservation

The thrush is classified as near threatened because it has a small population with a restricted range. Predation by black rats on Tristan is an ongoing threat, though the other islands it occupies are rat-free. The feral cats that previously occupied Tristan have been eradicated. Conservation recommendations by BirdLife International are to continue regular population monitoring, to control rats on Tristan, and to prevent further introductions of mammalian predators. [6]

Population

A survey in 1972–1974 estimated the separate island populations as Tristan 40–60 pairs, Inaccessible 100–500 pairs, Nightingale 300–500 pairs, Middle 20–40 pairs and Stoltenhoff 10–20 pairs. In the 1980s the population of Inaccessible Island was revised to 850 pairs, and the total population for the whole group to about 6,000 individual birds. More recently, the number of birds on Tristan has been roughly estimated at several hundred. The population is stable with no evidence of decline in numbers or range. [6]

Related Research Articles

<span class="mw-page-title-main">Tristan da Cunha</span> South Atlantic island group

Tristan da Cunha, colloquially Tristan, is a remote group of volcanic islands in the South Atlantic Ocean. It is the most remote inhabited archipelago in the world, lying approximately 2,787 kilometres (1,732 mi) from Cape Town in South Africa, 2,437 kilometres (1,514 mi) from Saint Helena, 3,949 kilometres (2,454 mi) from Mar del Plata in Argentina, and 4,002 kilometres (2,487 mi) from the Falkland Islands.

<span class="mw-page-title-main">Thrush (bird)</span> Family of birds

The thrushes are a passerine bird family, Turdidae, with a worldwide distribution. The family was once much larger before biologists reclassified the former subfamily Saxicolinae, which includes the chats and European robins, as Old World flycatchers. Thrushes are small to medium-sized ground living birds that feed on insects, other invertebrates, and fruit. Some unrelated species around the world have been named after thrushes due to their similarity to birds in this family.

<span class="mw-page-title-main">Inaccessible Island rail</span> Bird species endemic to the south Atlantic

The Inaccessible Island rail is a small bird of the rail family, Rallidae. Endemic to Inaccessible Island in the Tristan Archipelago in the isolated south Atlantic, it is the smallest extant flightless bird in the world. The species was formally described by physician Percy Lowe in 1923 but had first come to the attention of scientists 50 years earlier. The Inaccessible Island rail's taxonomic affinities and origin were a long-standing mystery; in 2018 its closest relative was identified as the South American dot-winged crake, and it was decided that both species are best classified in the genus Laterallus.

<span class="mw-page-title-main">Gough Island</span> Island in the South Atlantic

Gough Island, also known historically as Gonçalo Álvares, is a rugged volcanic island in the South Atlantic Ocean. It is a dependency of Tristan da Cunha and part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha. It is approximately 400 km (250 mi) south-east of the Tristan da Cunha archipelago, 2,400 km (1,500 mi) north-east from South Georgia Island, 2,700 km (1,700 mi) west from Cape Town, and over 3,200 km (2,000 mi) from the nearest point of South America.

<span class="mw-page-title-main">Inaccessible Island</span> Island in Tristan da Cunha archipelago

Inaccessible Island is a volcanic island located in the South Atlantic Ocean, 31 km (19 mi) south-west of Tristan da Cunha. Its highest point, Swale's Fell, reaches 581 m (1,906 ft), and the island is 12.65 km2 (4.88 sq mi) in area. The volcano was last active approximately one million years ago and is now extinct.

<span class="mw-page-title-main">Nightingale Island</span> Volcanic island in the South Atlantic Ocean

Nightingale Island is an active volcanic island in the South Atlantic Ocean, 3 square kilometres (1.2 sq mi) in area, part of the Tristan da Cunha group of islands. They are administered by the United Kingdom as part of the overseas territory of Saint Helena, Ascension and Tristan da Cunha.

<span class="mw-page-title-main">Spectacled petrel</span> Species of bird

The spectacled petrel is a rare seabird that nests only on the high western plateau of Inaccessible Island in the South Atlantic Tristan da Cunha group. It is one of the largest petrels that nests in burrows. This species was formerly considered to be a subspecies of the white-chinned petrel.

<span class="mw-page-title-main">Nightingale Islands</span> Island group in Tristan da Cunha archipelago

The Nightingale Islands are a group of three islands in the South Atlantic Ocean, part of the Tristan da Cunha territory. They consist of Nightingale Island, Middle Island and Stoltenhoff Island. The islands are administered by the United Kingdom as part of the overseas territory of Saint Helena, Ascension and Tristan da Cunha. The Nightingale Islands are uninhabited.

<span class="mw-page-title-main">Atlantic yellow-nosed albatross</span> Large seabird from the south Atlantic

The Atlantic yellow-nosed albatross is a large seabird in the albatross family Diomedeidae.

<span class="mw-page-title-main">Stoltenhoff Island</span> Island in Tristan da Cunha archipelago

Stoltenhoff Island is a small uninhabited island in the South Atlantic Ocean, part of the Nightingale Islands. It is the smallest of the Nightingale Islands, and is to the northwest of Nightingale Island itself. They are governed as part of Tristan da Cunha, an archipelago and part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha. The island is part of the Nightingale Islands group Important Bird Area (IBA), identified as such by BirdLife International as a breeding site for seabirds and endemic landbirds.

<span class="mw-page-title-main">Atlantic petrel</span> Species of bird

The Atlantic petrel is a gadfly petrel endemic to the South Atlantic Ocean. It breeds in enormous colonies on Tristan da Cunha and Gough Island, and ranges at sea from Brazil to Namibia, with most records at sea being to the west of the breeding islands, and along the subtropical convergence. Adults are about 43 cm long, powerful, large, stocky, dark in color with white belly. Their head can appear to be grey in worn plumage. Brown undercoating of wings and tail. These petrels can live on average of 15 years of age.

Saint Helena, Ascension Island and Tristan da Cunha, as well the other uninhabited islands nearby, are a haven for wildlife in the middle of the Atlantic Ocean. The islands are or were home to much endemic flora and fauna, especially invertebrates, and many endemic fish species are found in the reef ecosystems off the islands. The islands have been identified by BirdLife International as Important Bird Areas for both their endemic landbirds and breeding seabirds.

<span class="mw-page-title-main">Grey petrel</span> Species of bird

The grey petrel, also called the brown petrel, pediunker or grey shearwater is a species of seabird in the Procellariidae, or petrel family. It is pelagic and occurs in the open seas of the Southern Hemisphere, mainly between 32°S and 58°S.

<span class="mw-page-title-main">Ecuadorian thrush</span> Species of bird

The Ecuadorian thrush is a resident bird found in western South America in western Ecuador and far northwestern Peru. It was formerly considered to be a subspecies of the spectacled thrush, Turdus nudigenis, but has a narrower eyering, and is widely separated in range.

<span class="mw-page-title-main">Northern rockhopper penguin</span> Species of bird

The northern rockhopper penguin, Moseley's rockhopper penguin, or Moseley's penguin is a penguin species native to the southern Indian and Atlantic Oceans. It is described as distinct from the southern rockhopper penguin.

<span class="mw-page-title-main">Geography of Tristan da Cunha</span>

Tristan da Cunha is an archipelago of five islands in the southern Atlantic Ocean, the largest of which is the island of Tristan da Cunha itself and the second-largest, the remote bird haven, Gough Island. It forms part of a wider territory called Saint Helena, Ascension and Tristan da Cunha which includes Saint Helena and Ascension Island.

<span class="mw-page-title-main">Tristan da Cunha–Gough Islands shrub and grasslands</span>

The Tristan da Cunha–Gough Islands shrub and grasslands is a terrestrial ecoregion which covers the Tristan da Cunha archipelago and Gough Island in the South Atlantic Ocean. The islands' remote location gave rise to many endemic species.

References

Notes

  1. 1 2 BirdLife International (2017). "Turdus eremita". IUCN Red List of Threatened Species . 2017: e.T22708541A117286443. doi: 10.2305/IUCN.UK.2017-3.RLTS.T22708541A117286443.en . Retrieved 14 November 2021.
  2. 1 2 3 Hince (2000).
  3. 1 2 Voelker et al. (2007).
  4. Sinclair, I. (1994). Field Guide to Birds of Southern Africa (3 ed.). Struik Publishers. p. 339. ISBN   1-86825-510-7.
  5. Zoological Museum, University of Amsterdam.
  6. 1 2 3 4 5 6 BirdLife International (2010).
  7. 1 2 Internet Bird Collection.
  8. 1 2 Cooper (2010).
  9. Ryan & Ronconi (2010).
  10. "BBC Four - Britain's Treasure Islands, Southern Ocean". Bbc.co.uk. Retrieved 2016-11-27.
  11. Taylor, B; Sharpe, C. J. (2017). "Inaccessible Rail (Atlantisia rogersi)" . Handbook of the Birds of the World Alive. Barcelona: Lynx Edicions. doi:10.2173/bow.inirai1.01. S2CID   243565508 . Retrieved 3 June 2017.

Sources

Commons-logo.svg Media related to Turdus eremita at Wikimedia Commons