Tristan Thrush
Encyclopedia
The Tristan Thrush also known as the Starchy, is a species
of bird
in the thrush
family
that is endemic to the isolated Tristan da Cunha
archipelago
in the South Atlantic Ocean
.
as being similar in size and appearance to the Song Thrush
, and by Henry Moseley
as like a very dark-coloured Song Thrush. 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.
The nominate subspecies from Tristan differs from that from Nightingale, 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 appear to be intermediate, with the sides of the head of a specimen from there speckled both rufous and fuscous.
, Nightingale
, Middle
and Stoltenhoff Island
s in the Tristan group. It uses all the natural habitat
s available on the islands, including rocky shorelines, tussock
grassland
, fern
-dominated shrubland
and wet heathland
.
, but its adaptations to life on a small island group, including an unusual brush-tipped tongue
modified for extracting the contents of sggs, have been used as reasons to warrant its separation into the monotypic
genus
Nesocichla. 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 and should be subsumed in it as T. eremita.
There are three subspecies, the ranges of which correspond to the three main islands in the group:
period is about 20 days.
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. 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.
because it has a small population with a restricted range. Predation by Black Rat
s on Tristan is an ongoing threat, though the other islands it occupies are rat-free. The feral cat
s 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.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of bird
Bird
Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...
in the thrush
Thrush (bird)
The thrushes, family Turdidae, are a group of passerine birds that occur worldwide.-Characteristics:Thrushes are plump, soft-plumaged, small to medium-sized birds, inhabiting wooded areas, and often feed on the ground or eat small fruit. The smallest thrush may be the Forest Rock-thrush, at and...
family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
that is endemic to the isolated Tristan da Cunha
Tristan da Cunha
Tristan da Cunha is a remote volcanic group of islands in the south Atlantic Ocean and the main island of that group. It is the most remote inhabited archipelago in the world, lying from the nearest land, South Africa, and from South America...
archipelago
Archipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
in the South Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
.
Description
The bird was described by John GouldJohn Gould
John Gould was an English ornithologist and bird artist. The Gould League in Australia was named after him. His identification of the birds now nicknamed "Darwin's finches" played a role in the inception of Darwin's theory of evolution by natural selection...
as being similar in size and appearance to the Song Thrush
Song Thrush
The Song Thrush is a thrush that breeds across much of Eurasia. It is also known in English dialects as throstle or mavis. It has brown upperparts and black-spotted cream or buff underparts and has three recognised subspecies...
, and by Henry Moseley
Henry Nottidge Moseley
Henry Nottidge Moseley, FRS was a British naturalist who sailed on the global scientific expedition of the HMS Challenger in 1872 through 1876....
as like a very dark-coloured Song Thrush. 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.
The nominate subspecies from Tristan differs from that from Nightingale, with the Tristan birds being warm dark brown on the upperparts rather than dull sooty-brown, rufous
Rufous
Rufous is a colour that may be described as reddish-brown or brownish-red, as of rust or oxidised iron.The first recorded use of rufous as a colour name in English was in the year 1782....
rather than dark fuscous on the sides of the head, and rufous-brown, rather than brownish-black, on the underparts. Birds from Inaccessible appear to be intermediate, with the sides of the head of a specimen from there speckled both rufous and fuscous.
Distribution and habitat
The thrush is found on Tristan, InaccessibleInaccessible Island
Inaccessible Island is an extinct volcano, 14 km² in area, rising out of the South Atlantic Ocean 45 km southwest of Tristan da Cunha. Inaccessible Island is located at . It is part of the archipelago of Tristan da Cunha, which is part of the overseas territory of the United Kingdom,...
, Nightingale
Nightingale Island
Nightingale Island is an island in the South Atlantic Ocean, 3 km² 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....
, Middle
Middle Island, Tristan da Cunha
Middle Island is a small, uninhabited island in the South Atlantic Ocean, part of the Nightingale Islands. They are governed as part of Tristan da Cunha, an archipelago that is part of the British overseas territory of Saint Helena, Ascension and Tristan da Cunha.-External links:*...
and Stoltenhoff Island
Stoltenhoff Island
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 north west of Nightingale Island itself...
s in the Tristan group. It uses all the natural habitat
Habitat
* Habitat , a place where a species lives and grows*Human habitat, a place where humans live, work or play** Space habitat, a space station intended as a permanent settlement...
s available on the islands, including rocky shorelines, tussock
Tussock
Tussock most often refers to a small hillock of grassy, or grass-like plant growth, but may also refer to Plants and ecology, Insects.- Plants and ecology :*Tussock *New Zealand tussock grasslands*Serrated Tussock...
grassland
Grassland
Grasslands are areas where the vegetation is dominated by grasses and other herbaceous plants . However, sedge and rush families can also be found. Grasslands occur naturally on all continents except Antarctica...
, fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
-dominated shrubland
Shrubland
Shrubland, scrubland, scrub or brush is a plant community characterized by vegetation dominated by shrubs, often also including grasses, herbs, and geophytes. Shrubland may either occur naturally or be the result of human activity...
and wet heathland
Heath (habitat)
A heath or heathland is a dwarf-shrub habitat found on mainly low quality acidic soils, characterised by open, low growing woody vegetation, often dominated by plants of the Ericaceae. There are some clear differences between heath and moorland...
.
Taxonomy
The thrush is thought to have evolved from an ancestor in the genus Turdus from South America, and resembles an immature Austral ThrushAustral Thrush
The Austral Thrush, Turdus falcklandii, is a medium sized thrush from southern South America. There are two subspecies, the Magellan Thrush from south Argentina and south and central Chile, and the Falkland Thrush The Austral Thrush, Turdus falcklandii, is a medium sized thrush from southern South...
, but its adaptations to life on a small island group, including an unusual brush-tipped tongue
Tongue
The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...
modified for extracting the contents of sggs, have been used as reasons to warrant its separation into the monotypic
Monotypic
In biology, a monotypic taxon is a taxonomic group with only one biological type. The term's usage differs slightly between botany and zoology. The term monotypic has a separate use in conservation biology, monotypic habitat, regarding species habitat conversion eliminating biodiversity and...
genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
Nesocichla. However, molecular analysis has indicated that not only is it part of a South American clade
Clade
A clade is a group consisting of a species and all its descendants. In the terms of biological systematics, a clade is a single "branch" on the "tree of life". The idea that such a "natural group" of organisms should be grouped together and given a taxonomic name is central to biological...
of Turdus, but also that it falls squarely within that genus and should be subsumed in it as T. eremita.
There are three subspecies, the ranges of which correspond to the three main islands in the group:
- N. e. eremita Gould, 1855 (Tristan da Cunha)
- N. e. gordoni Stenhouse, 1924 (Inaccessible Island)
- N. e. procax Elliott, 1954 (Nightingale, Middle and Stoltenhoff Islands)
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 fledgingFledge
Fledge is the stage in a young bird's life when the feathers and wing muscles are sufficiently developed for flight. It also describes the act of a chick's parents raising it to a fully grown state...
period is about 20 days.
Feeding
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, the eggs and fledglings of other birds, and kitchen scraps.Seabird predation
Ardea (journal)
Ardea is a peer-reiewed scientific journal and the official publication of the Netherlands Ornithologists' Union, having been published by that body since 1912. It is published twice a year and contains articles on birds, in particular relating to their ecology, life history, and evolution. It also...
reported an observation of Tristan Thrushes breaking open an egg of the Atlantic Yellow-nosed Albatross
Atlantic Yellow-nosed Albatross
The Atlantic Yellow-nosed Albatross, Thalassarche chlororhynchos, is a large seabird in the albatross family. This small mollymawk was once considered conspecific with the Indian Yellow-nosed Albatross and known as the Yellow-nosed Albatross...
. They also found that the thrush is a regular predator of the eggs and small chicks of the Great Shearwater
Great Shearwater
The Great Shearwater is a large shearwater in the seabird family Procellariidae. Its relationships are unclear. It belongs in the group of large species that could be separated as genus Ardenna ; within these, it might be allied with the other black-billed, blunt-tailed species Short-tailed...
, being responsible for almost half of the egg losses by that species during the early incubation period in a colony on Inaccessible Island. They saw evidence that the thrushes remove eggs of the Spectacled Petrel
Spectacled Petrel
The Spectacled Petrel, Procellaria conspicillata, is a rare seabird that nests only on the high western plateau of Inaccessible Island in the Tristan da Cunha group. It is one of the largest petrels that nest in burrows.-Description:...
(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.
Status and conservation
The thrush is classified as near threatenedNear Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
because it has a small population with a restricted range. Predation by Black Rat
Black Rat
The black rat is a common long-tailed rodent of the genus Rattus in the subfamily Murinae . The species originated in tropical Asia and spread through the Near East in Roman times before reaching Europe by the 1st century and spreading with Europeans across the world.-Taxonomy:The black rat was...
s on Tristan is an ongoing threat, though the other islands it occupies are rat-free. The feral cat
Feral cat
A feral cat is a descendant of a domesticated cat that has returned to the wild. It is distinguished from a stray cat, which is a pet cat that has been lost or abandoned, while feral cats are born in the wild; the offspring of a stray cat can be considered feral if born in the wild.In many parts of...
s 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.