Chatham Gerygone
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The Chatham Islands gerygone (''Gerygone albofrontata''), also known as the Chatham gerygone or Chatham Island warbler, is a species of bird in the family
Acanthizidae Acanthizidae—sometimes called Australian warblers—are a family of passerine birds which includes gerygones, thornbills '' Acanthiza'', and scrubwrens '' Sericornis''. The family Acanthizidae consists of small to medium passerine birds, with ...
. It is
endemic Endemism is the state of a species being found only 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 foun ...
to the
Chatham Islands The Chatham Islands ( ; Moriori language, Moriori: , 'Misty Sun'; ) are an archipelago in the Pacific Ocean about east of New Zealand's South Island, administered as part of New Zealand, and consisting of about 10 islands within an approxima ...
. The Chatham Islands gerygone is larger than and differs in plumage from the related
grey warbler The grey warbler (''Gerygone igata''), also known by its Māori name or outside New Zealand as the grey gerygone, is an insectivorous bird in the family Acanthizidae endemic to New Zealand. It is sometimes known as the teetotum or rainbird. I ...
of mainland New Zealand. Both warblers were discovered and named by G. R. Gray in 1845. The grey and Chatham Island warblers are the only two members of the Australasian family
Acanthizidae Acanthizidae—sometimes called Australian warblers—are a family of passerine birds which includes gerygones, thornbills '' Acanthiza'', and scrubwrens '' Sericornis''. The family Acanthizidae consists of small to medium passerine birds, with ...
found in New Zealand.


Description

The Chatham Islands gerygone has a plain olive-brown head and upperparts, with off-white underparts interrupted by pale yellow flanks and undertail. The male warbler has a distinctive white forehead, eyebrows, throat and underparts. The female warbler lacks these white areas, instead showing dull greyish-white underparts and yellow eyebrows, cheek and throat. Both adults have red eyes. This species of warbler also shows variation in the plumage of the juvenile bird. More akin to the female colouration, the juveniles have olive-grey upperparts and more yellow through their underparts, with brown eyes. Adult Chatham Islands gerygones of both sexes are about long, but the male slightly outweighs the female adult, with average weights of and respectively. The call of the Chatham Islands gerygone is delicate and intricate. The bird song is said to be similar to that heard from grey warblers that haven't graduated into full song, with initial phrases of four notes recurring throughout the tune. This distinctive call was said to be used by
Māori Māori or Maori can refer to: Relating to the Māori people * Māori people of New Zealand, or members of that group * Māori language, the language of the Māori people of New Zealand * Māori culture * Cook Islanders, the Māori people of the Co ...
to act as a reminder for when the time came to plant their crops.


Distribution

Its natural
habitat In ecology, habitat refers to the array of resources, 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 manifestation of its ...
is temperate
forest A forest is an ecosystem characterized by a dense ecological community, community of trees. Hundreds of definitions of forest are used throughout the world, incorporating factors such as tree density, tree height, land use, legal standing, ...
s. Widespread in the southern forest of the main Chatham Island, the warblers are also seen on surrounding islands such as
Pitt Island Pitt Island ( Moriori: , ) is the second largest island in New Zealand's Chatham Islands, with an area of . It lies about to the east of New Zealand's main islands, and about to the southeast of Chatham Island, from which it is separated by ...
,
Little Mangere Island Little Mangere is a small island of the Chatham Archipelago, just off the western end of Mangere Island, about 4 km (2½ mi) west of Pitt Island and south-east of the town of Waitangi on Chatham Island. The island is called ''Tapuaenuku ...
,
Star Keys The Star Keys (; Moriori: )Government of New Zealand, Dept. of Conservation (1999) Chatham IslandsConservation Management Strategy map 6. Accessed on 2012-07-13. are group of five rocky islets in the Chatham Archipelago, about east of Pitt Isl ...
, and
Rangatira In Māori culture, () are tribal chiefs, the leaders (often hereditary) of a (subtribe or clan). Ideally, were people of great practical wisdom who held authority () on behalf of the tribe and maintained boundaries between a tribe's land ( ...
. Habitat loss and predators are the main causes for the northern boundary seen on the main island.


Behaviour and ecology

The Chatham Islands gerygone's diet consists of small insects such as caterpillars, flies and beetles, and spiders. They feed mainly in the canopy, taking insects from leaves and tree branch crevices, and are also seen to browse the leaf litter. Unlike the grey warbler, the Chatham Islands gerygone does not hover to collect insects. Chatham Islands gerygones are known to occasionally have their nests parasitized by
Shining Bronze-cuckoo The shining bronze cuckoo (''Chalcites lucidus'') is a species of cuckoo in the family Cuculidae, found in Australia, Indonesia, New Caledonia, New Zealand, Papua New Guinea, Solomon Islands, and Vanuatu. It was formerly placed in the genus ''Chr ...
s (Chrysococcyx lucidus). The cuckoo lays an egg in a nest, and hatching first the chick consequently pushes the warbler eggs out of the nest. The cuckoo chick is then fed and raised by the adult warblers. Other threats include rats, cats, and most significantly, habitat reduction.


Breeding

Chatham Islands gerygones are solitary nesters, with defined territories defended against conspecifics. Disputes are mainly carried out by the male birds, and you can observe long chases occurring when boundaries are threatened. Although very territorial, boundary disputes never result in contact. The warblers are
monogamous Monogamy ( ) is a relationship of two individuals in which they form a mutual and exclusive intimate partnership. Having only one partner at any one time, whether for life or serial monogamy, contrasts with various forms of non-monogamy (e.g. ...
and the same breeding territories have been known to be defended for up to three years in a row. The
breeding season Seasonal breeders are animal species that successfully mate only during certain times of the year. These times of year allow for the optimization of survival of young due to factors such as ambient temperature, food and water availability, and ch ...
for these warblers varies from year to year, but can be seen to average from around September to January. The nest style produced is the enclosed pendant, very similar to that of the grey warbler. The female birds are the sole nest builders, and incorporate mosses, lichens, leaves, bark, feathers, small twigs and spider webs into the nests. The nests are also seen to be lined with soft feathers. The location of the nests differs depending on the island. Nests on the largest island tend to be hanging freely in the open and in gaps of vegetation, while nests on the surrounding islands are in dense foliage. The female is in charge of brooding, and her eggs are an off-white colour flecked with reddish brown. On hatching, both male and female contribute by feeding the chicks. The Chatham Islands gerygone has a high breeding success rate of 87%, significantly higher than the mainland grey warbler which sees only 38% breeding success.


Status and conservation

Thriving in predator-free habitats, the adult warbler population is estimated at around 5000 birds. Although thought to be decreasing, the population numbers have not yet reduced enough to be classified as vulnerable by the IUCN and it is thus categorised as "least concern" on the red list of threatened species. Although this is the case, a recovery plan has been in place in New Zealand due to habitat loss. Main efforts have involved restoring the warblers to the northern sites of Chatham Island, and reforestation to provide future habitats for the population. Control of pests such as cats and
weka The weka, also known as the Māori hen or woodhen (''Gallirallus australis'') is a flightless bird species of the rail family. It is endemic to New Zealand. Some authorities consider it as the only extant member of the genus '' Gallirallus''. ...
have also been a focus, although the canopy dwelling birds aren't often affected by these.


References


External links

* {{Taxonbar, from=Q1301862 Gerygone Birds of the Chatham Islands Birds described in 1844 Taxa named by George Robert Gray Taxonomy articles created by Polbot Endemic birds of New Zealand