The Tristan thrush (''Turdus eremita''), also known as the starchy,
[Hince (2000).] is a
species
In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
of
bird
Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweigh ...
in the
thrush family
Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...
that is
endemic
Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found elsew ...
to the
British overseas territories
The British Overseas Territories (BOTs), also known as the United Kingdom Overseas Territories (UKOTs), are fourteen dependent territory, territories with a constitutional and historical link with the United Kingdom. They are the last remna ...
of the isolated
Tristan da Cunha
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 from Cape Town in South Africa, from Saint Helena ...
archipelago
An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster, or collection of islands, or sometimes a sea containing a small number of scattered islands.
Examples of archipelagos include: the Indonesian Archi ...
in the
South Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's five oceans, with an area of about . It covers approximately 20% of Earth's surface and about 29% of its water surface area. It is known to separate the "Old World" of Africa, Europe and ...
.
Description
The bird was described by
John Gould
John Gould (; 14 September 1804 – 3 February 1881) was an English ornithologist. He published a number of monographs on birds, illustrated by plates produced by his wife, Elizabeth Gould, and several other artists, including Edward Lear, ...
as being similar in size and appearance to the
song thrush
The song thrush (''Turdus philomelos'') is a Thrush (bird), thrush that breeds across the West Palearctic. It has brown upper-parts and black-spotted cream or buff underparts and has three recognised subspecies. Its distinctive Birdsong, song, ...
, and by
Henry Moseley
Henry Gwyn Jeffreys Moseley (; 23 November 1887 – 10 August 1915) was an English physicist, whose contribution to the science of physics was the justification from physical laws of the previous empirical and chemical concept of the atomic num ...
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.][
This thrush typically has a length of about . The ]nominate subspecies
In biological classification, subspecies is a rank below species, used for populations that live in different areas and vary in size, shape, or other physical characteristics (morphology), but that can successfully interbreed. Not all species ...
from Tristan differs from that from Nightingale Island
Nightingale Island is an active volcanic island in the South Atlantic Ocean, 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 Tri ...
, with the Tristan birds being warm dark brown on the upperparts rather than dull sooty-brown, rufous
Rufous () is a color that may be described as reddish-brown or brownish-red, as of rust or oxidised iron. The first recorded use of ''rufous'' as a color name in English was in 1782. However, the color is also recorded earlier in 1527 as a dia ...
rather than dark fuscous on the sides of the head, and rufous-brown, rather than brownish-black, on the underparts. Birds from Inaccessible Island
Inaccessible Island is a volcanic island located in the South Atlantic Ocean, south-west of Tristan da Cunha. Its highest point, Cairn Peak, reaches , and the island is in area. The volcano was last active six million years ago and is curren ...
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, Inaccessible, Nightingale, Middle and 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. They are governed as part of Tr ...
s in the Tristan group. It uses all the natural habitat
In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
s available on the islands, including rocky shorelines, tussock grassland
A grassland is an area where the vegetation is dominated by grasses (Poaceae). However, sedge (Cyperaceae) and rush (Juncaceae) can also be found along with variable proportions of legumes, like clover, and other herbs. Grasslands occur natur ...
, fern
A fern (Polypodiopsida or Polypodiophyta ) is a member of a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. The polypodiophytes include all living pteridophytes except t ...
-dominated shrubland
Shrubland, scrubland, scrub, brush, or bush 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. It m ...
and wet heathland
A heath () is a shrubland habitat found mainly on free-draining infertile, acidic soils and characterised by open, low-growing woody vegetation. Moorland is generally related to high-ground heaths with—especially in Great Britain—a cooler ...
.[
]
Taxonomy
The thrush is thought to have evolved from an ancestor in the genus ''Turdus
True thrushes are medium-sized mostly insectivorous or omnivorous birds in the genus ''Turdus'' of the wider thrush family, Turdidae. The genus name ''Turdus'' is Latin for "thrush". The term " thrush" is used for many other birds of the family T ...
'' from South America, and resembles an immature austral thrush
The austral thrush (''Turdus falcklandii'') is a medium-sized thrush from southern South America. There are two subspecies, the Magellan thrush (''T. f. magellanicus'') from south Argentina and south and central Chile, and the Falkland thrush ('' ...
, but its adaptations to life on a small island group, including an unusual brush-tipped tongue
The tongue is a muscular organ (anatomy), organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive system, digestive process, and is the primary organ of taste. The tongue's upper surfa ...
modified for extracting the contents of eggs, have been used as reasons to warrant its separation into the monotypic
In biology, a monotypic taxon is a taxonomic group (taxon) that contains only one immediately subordinate taxon. A monotypic species is one that does not include subspecies or smaller, infraspecific taxa. In the case of genera, the term "unispec ...
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''Nesocichla''.[ However, molecular analysis has indicated that not only is it part of a South American ]clade
A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...
of ''Turdus'', but also that it falls squarely within that genus.[Voelker et al. (2007).]
There are three subspecies, the ranges of which correspond to the three main islands in the group:[BirdLife International (2010).][Internet Bird Collection.]
* ''Turdus eremita eremita'' Gould, 1855 (Tristan da Cunha)
* ''Turdus eremita gordoni'' Stenhouse, 1924 (Inaccessible Island)
* ''Turdus eremita procax'' Elliott, 1954 (Nightingale, Middle and Stoltenhoff Islands)
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
Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight.
This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnerable c ...
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
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
The Atlantic yellow-nosed albatross (''Thalassarche chlororhynchos'') is a large seabird in the albatross family Diomedeidae.
This small mollymawk was once considered conspecific with the Indian yellow-nosed albatross and known as the yellow-no ...
. They also found that the thrush is a regular predator of the eggs and small chicks of the great shearwater
The great shearwater (''Ardenna gravis'') is a large shearwater in the seabird family Procellariidae. It breeds colonially on rocky islands in the south Atlantic. Outside the breeding season it ranges widely in the Atlantic.
Taxonomy
The great s ...
, 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 petrel
The white-faced storm petrel (''Pelagodroma marina''), also known as white-faced petrel is a small seabird of the austral storm petrel family Oceanitidae. It is the only member of the monotypic genus ''Pelagodroma''.
Description
The white-faced ...
s directly, probably by taking them from their burrows.[Cooper (2010).] Furthermore, they have been observed to drink blood from penguins.
Status and conservation
The thrush is classified as near threatened
A near-threatened species is a species which has been categorized as "Near Threatened" (NT) by the International Union for Conservation of Nature as that may be vulnerable to endangerment in the near future, but it does not currently qualify fo ...
because it has a small population with a restricted range. Predation by black rat
The black rat (''Rattus rattus''), also known as the roof rat, ship rat, or house rat, is a common long-tailed rodent of the stereotypical rat genus ''Rattus'', in the subfamily Murinae. It likely originated in the Indian subcontinent, but is n ...
s on Tristan is an ongoing threat, though the other islands it occupies are rat-free. The feral cat
A feral cat or a stray cat is an unowned domestic cat (''Felis catus'') that lives outdoors and avoids human contact: it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens ...
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.[
]
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.[
]
References
Notes
Sources
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External links
Photos, Videos and Spottings
on Birds of the world
Image of specimen at the University of Amsterdam
{{Taxonbar, from=Q27075632
Birds described in 1855
Birds of islands of the Atlantic Ocean
Birds of subantarctic islands
Turdidae
Taxonomy articles created by Polbot
Endemic fauna of Tristan da Cunha