New Zealand wren

The New Zealand wrens are a family (Acanthisittidae) of tiny passerines endemic to New Zealand. They were represented by six known species in four or five genera, although only two species survive in two genera today. They are understood to form a distinct lineage within the passerines, but authorities differ on their assignment to the oscines or suboscines (the two suborders that between them make up the Passeriformes). More recent studies suggest that they form a third, most ancient, suborder Acanthisitti and have no living close relatives at all. They are called "wrens" due to similarities in appearance and behaviour to the true wrens (Troglodytidae), but are not members of that family.

New Zealand wrens are mostly insectivorous foragers of New Zealand’s forests, with one species, the New Zealand rock wren, being restricted to alpine areas. Both the remaining species are poor fliers and four of the five extinct species are known to be, or are suspected of having been, flightless (based on observations of living birds and the size of their sterna); along with the long-legged bunting from Tenerife, one of the Canary Islands, they are the only passerines known to have lost the ability to fly. Of the species for which the plumage is known, they are drab-coloured birds with brown-green plumage. They form monogamous pair bonds to raise their young, laying their eggs in small nests in trees or amongst rocks. They are diurnal and like all New Zealand passerines, for the most part, are sedentary.

New Zealand wrens, like many New Zealand birds, suffered several extinctions after the arrival of humans in New Zealand. Two species became extinct after the arrival of the Māori and the Polynesian rat and are known today only from fossil remains; a third, Lyall's wren, became extinct on the main islands, surviving only as a relict population on Stephens Island in the Cook Strait. This species and the bushwren became extinct after the arrival of Europeans, with the bushwren surviving until 1972. Of the two remaining species, the rifleman is still common in both the North and South Islands, while the New Zealand rock wren is restricted to the alpine areas of the South Island and is considered vulnerable.

New Zealand wrens
Temporal range: Miocene to present
Rock wren
The winter range of the New Zealand rock wren remains a scientific mystery
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Aves
Order: Passeriformes
Suborder: Acanthisitti
Family: Acanthisittidae
Sundevall, 1872
Genera

Acanthisitta
Xenicus
daggerTraversia
daggerPachyplichas
daggerDendroscansor
daggerKuiornis

Taxonomy and systematics

The taxonomy of the New Zealand wrens has been a subject of considerable debate since their discovery, although they have long been known to be an unusual family. In the 1880s, Forbes assigned the New Zealand wrens to the suboscines related to the cotingas and the pittas (and gave the family the name Xenicidae). Later, they were thought to be closer to the ovenbirds and antbirds. Sibley’s 1970 study comparing egg-white proteins moved them to the oscines, but later studies, including the 1982 DNA-DNA hybridization study, suggested the family was a sister taxon to the subocines and the oscines. This theory has proven most robust since then and the New Zealand wrens might be the survivors of a lineage of passerines that was isolated when New Zealand broke away from Gondwana 82–85 million years ago (Mya),[1] though a pre-Paleogene origin of passerines is highly disputed and tends to be rejected in more recent studies.

As no evidence indicates passerines were flightless when they arrived on New Zealand (that apomorphy is extremely rare and unevenly distributed in Passeriformes), they are not required by present theories to have been distinct in the Mesozoic. As unequivocal Passeriformes are known from Australia some 55 Mya, the acanthisittids' ancestors likely arrived in the Late Paleocene from Australia or the then-temperate Antarctic coasts. Plate tectonics indicate that the shortest distance between New Zealand and those two continents was roughly 1,500 km (1,000 miles) at that time. New Zealand's minimum distance from Australia is a bit more today – some 1,700 km/1,100 miles - whereas it is now at least 2,500 km (1,550 miles) from Antarctica.

The extant species are closely related and thought to be descendants of birds that survived a genetic bottleneck caused by the marine transgression during the Oligocene, when most of New Zealand was under water.[2] The earliest known fossil is Kuiornis indicator from the Miocene Saint Bathans Fauna.[3]

The relationships between the genera and species are poorly understood. The extant genus Acanthisitta has one species, the rifleman and the other surviving genus, Xenicus, includes the New Zealand rock wren and the recently extinct bushwren. Some authorities have retained Lyall's wren in Xenicus as well, but it is often afforded its own monotypic genus, Traversia. The stout-legged wren (genus Pachyplichas) was originally split into two species, but more recent research disputes this.[4] The final genus was Dendroscansor, which had one species, the long-billed wren.[5]

Species

Description

Reiflman Acanthisitta chloris crop
Female riflemen are larger than the males.

New Zealand wrens are tiny birds; the rifleman is the smallest of New Zealand's birds. Their length ranges from 7 to 10 cm and their weight from as little as 5–7 g for the rifleman to an estimated 50 g for the extinct stout-legged wren. The New Zealand rock wren (and probably the bushwren) weighs between 14 and 22 g and the extinct long-billed wren weighed around 30 g.

The plumage of the New Zealand wrens is only known for the four species seen by European scientists. All these species have dull green and brown plumage and all except Lyall's wren have a prominent supercilium above the eye. The plumage of males and females were alike in Lyall's wren and the bushwren;[7][8] the New Zealand rock wren shows slight sexual dimorphism in its plumage and differences between the plumage of riflemen are pronounced, with the male having bright green upperparts and the female being duller and browner.

Both the New Zealand rock wren and the rifleman also show sexual dimorphism in size; unusually for passerines, the female is larger than the male.[7] The female rifleman also exhibits other differences from the male, having a slightly more upturned bill than the male and a larger hind claw.

The New Zealand wrens evolved in the absence of mammals for many millions of years and the family was losing the ability to fly. Three species are thought to have lost the power of flight: the stout-legged wren, the long-billed wren and Lyall's wren. The skeletons of these species have massively reduced keels in the sternum and the flight feathers of Lyall's wren also indicate flightlessness. Contemporary accounts of the Lyall's wrens on Stephens Island describe the species as scurrying on the ground rather than flying.

Distribution and habitat

The New Zealand wrens are endemic and restricted to the main and offshore islands of New Zealand; they have not been found on any of the outer islands such as the Chatham Islands or the Kermadec Islands. Prior to the arrival of humans in New Zealand (about A.D. 1280), they had a widespread distribution across both the North and South Islands and on Stewart Island/Rakiura. The range of the rifleman and bushwren included southern beech forest and podocarp-broadleaf forest, with the range of the bushwren also including coastal forest and scrub, particularly the Stewart Island subspecies. The New Zealand rock wren is specialised for the alpine environment, in areas of low scrub and scree from 900 m up to 2,400 m. Contrary to its other common name (the South Island wren), fossil evidence shows it was more widespread in the past and once lived in the North Island. Lyall's wren was once thought to have been restricted to the tiny Stephens Island in Cook Strait,[9] but fossil evidence has shown the species was once widespread in both the North and South Islands.[4] The stout-legged wren was similarly found on both islands, but fossils of the long-billed wren have only been found in the South Island. Fossils of the long-billed wren are far less common than those of the other species, in fact, its bones are the rarest fossil finds in New Zealand.[4]

After the wave of extinctions and range contractions caused by the arrival of mammals in New Zealand, the New Zealand wrens have a much reduced range. The New Zealand rock wren is now restricted to the South Island and is declining in numbers.[10] The range of the rifleman initially contracted with the felling of forests for agriculture, but it has also expanded its range of habitats by moving into plantations of introduced exotic pines, principally the Monterey pine. It also enters other human-modified habitat when it adjoins native forest.[7]

Like all New Zealand passerines, the New Zealand wrens are sedentary and are not thought to undertake any migrations. It is not known if the extinct species migrated, but it is considered highly unlikely, as three of the extinct species were flightless. The situation with the New Zealand rock wren is an ornithological mystery, as they are thought to live above the snow line where obtaining food during the winter would be extremely difficult. Searches have found no evidence that they move altitudinally during the winter, but they are also absent from their normal territories. They may enter a state of torpor (like the hummingbirds of the Americas or a number of Australian passerines) during at least part of the winter, but this has not yet been proved.[7]

References

  1. ^ Ericson P, Christidis L, Cooper, A, Irestedt M, Jackson J, Johansson US, Norman JA. (2002). A Gondwanan origin of passerine birds supported by DNA sequences of the endemic New Zealand wrens. Proc Biol Sci. 269(#1,488):235-41.
  2. ^ Cooper A. & Cooper R. (1995). The Oligocene Bottleneck and New Zealand Biota: Genetic Record of a past Environmental Crisis Proceedings of the Royal Society of London, Series B. 261(#1,362):293–302.
  3. ^ Worthy, Trevor H.; Hand, Suzanne J.; Nguyen, Jacqueline M. T.; Tennyson, Alan J. D.; Worthy, Jennifer P.; Scofield, R. Paul; Boles, Walter E.; Archer, Michael (2010). "Biogeographical and phylogenetic implications of an early Miocene wren (Aves: Passeriformes: Acanthisittidae) from New Zealand". Journal of Vertebrate Paleontology. 30 (#2): 479–498. doi:10.1080/02724631003618033.
  4. ^ a b c Worthy, Trevor H.; Richard N. Holdaway (2002). The Lost World of the Moa. Bloomington: Indiana University Press. pp. 424–427. ISBN 978-0-253-34034-4.
  5. ^ Milliner, P.R.; T. Worthy (1991). "Contributions to New Zealand's Late Quaternary avifauna. II, Dendroscansor decurvirostris, a new genus and species of wren (Aves : Acanthisittidae)". Journal of the Royal Society of New Zealand. 21 (#2): 179–200. doi:10.1080/03036758.1991.10431406.
  6. ^ "Stephens Island Rockwren (Traversia lyalli)".
  7. ^ a b c d Gill, B.J. (2004). "Family Acanthisittidae (New Zealand wrens)". In Josep, del Hoyo; Andrew, Elliott; David, Christie (eds.). Handbook of the Birds of the World. Volume 9. Cotingas to Pipits and Wagtails. Barcelona: Lynx Edicions. pp. 464–474. ISBN 978-84-87334-69-6.
  8. ^ Higgins P.J., Peter J.M & Steele W.K. (Eds) (2001). Handbook of Australian, New Zealand and Antarctic Birds. Volume 5: Tyrant-flycatchers to Chats. Oxford University press, Melbourne. ISBN 0-19-553244-9
  9. ^ Fuller, E. (2002). Foreword; Extinct Birds pp.11–69 in del Hoyo J., Elliott A. & Christie D.A. (2004). Handbook of the Birds of the World. Volume 7. Jamacars to Woodpeckers. Barcelona:Lynx Edicions. ISBN 84-87334-37-7
  10. ^ Michelsen-Heath, Sue; Peter G. Gaze (2007). "Changes in abundance and distribution of the rock wren (Xenicus gilviventris) in the South Island, New Zealand". Notornis. 54 (#2): 71–78.

External links

Long-billed wren (New Zealand)

The long-billed wren (Dendroscansor decurvirostris) was a species of New Zealand wren (family Acanthisittidae) endemic to the South Island of New Zealand. It was the only species in the genus Dendroscansor. The long-billed wren was a small bird with stout legs and tiny wings. Its reduced sternum suggests that it had weak flight muscles and was probably flightless, like the recently extinct Lyall's wren. Its weight is estimated at 30 g, which makes it heavier than any surviving New Zealand wren, but lighter than the also-extinct stout-legged wren. The bill of this species was both long and curved, unlike that of all other acanthisittid wrens.The species is known only from subfossils at four sites in Northwest Nelson and Southland; it seems to have been absent from the North Island and eastern South Island. The holotype was collected in 1986 from Moonsilver Cave, on Barrans Flat, near Takaka. It is the rarest fossil wren from New Zealand and presumably was the least common species when it was still extant. It is thought to have lived in high-altitude shrublands (like the surviving New Zealand rock wren) and perhaps montane southern beech forest.The long-billed wren went extinct before the arrival of European colonists and explorers in New Zealand. It was among the first wave of native bird species to go extinct after the introduction of Polynesian rats (or kiore). Like many New Zealand species, the long-billed wren presumably had few defences against novel predators such as rats.

Lyall's wren

Lyall's wren or the Stephens Island wren (Traversia lyalli) was a small flightless passerine belonging to the family Acanthisittidae, the New Zealand wrens. It was once found throughout New Zealand, but when it came to the attention of scientists in 1894 its last refuge was Stephens Island in Cook Strait. Often claimed to be a species discovered and driven extinct by a single creature (a lighthouse keeper's cat named Tibbles), the wren in fact fell victim to the island's numerous feral cats. The wren was described almost simultaneously by both Walter Rothschild and Walter Buller. It became extinct shortly after.

New Zealand rock wren

The New Zealand rock wren (Xenicus gilviventris) is a small New Zealand wren (family Acanthisittidae) endemic to the South Island of New Zealand. Its Māori names include pīwauwau ("little complaining bird"), mātuitui, and tuke ("twitch", after its bobbing motion). Outside New Zealand it is sometimes known as the rockwren or South Island wren to distinguish it from the unrelated rock wren of North America.

The rock wren is currently restricted to alpine and subalpine areas of the South Island; subfossil bones show it once lived in the North Island as well. It is a poor flier and highly terrestrial, feeding in low scrub, open scree, and rockfalls. The rock wren and rifleman are the only two surviving New Zealand wrens; the rock wren's closest relative was the now-extinct bushwren. Its numbers are declining due to predation by introduced mammals.

Pachyplichas

Pachyplichas is a genus containing two extinct species of New Zealand wren, a family of small birds endemic to New Zealand.

Pachyplichas jagmi

Pachyplichas jagmi is an extinct species of New Zealand wren, a family of small birds endemic to New Zealand.

St Bathans Fauna

The St Bathans Fauna is found in the lower Bannockburn Formation of the Manuherikia Group of Central Otago, in the South Island of New Zealand. It comprises a suite of fossilised prehistoric animals from the late Early Miocene (Altonian) period, with an age range of 19–16 million years ago.

The layer in which the fossils are found derives from littoral zone sediments deposited in a shallow, freshwater lake, with an area of 5600 km2 from present day Central Otago to Bannockburn and the Nevis Valley in the west; to Naseby in the east; and from the Waitaki Valley in the north to Ranfurly in the south. The lake was bordered by an extensive floodplain containing herbaceous and grassy wetland habitats with peat-forming swamp–woodland. At that time the climate was warm with a distinctly subtropical Australian climate and the surrounding vegetation was characterised by casuarinas, eucalypts and palms as well as podocarps, araucarias and southern beeches.

The fossiliferous layer has been exposed at places along the Manuherikia River and at other sites in the vicinity of the historic gold mining town of St Bathans. The fauna consists of a variety of vertebrates, including fish, a crocodilian, a rhynchocephalian (a relative of tuatara), geckos, skinks, and several kinds of birds, especially waterbirds. Of tree-dwelling birds, parrots outnumber pigeons thirty to one. Proapteryx, a basal form of kiwi, is known from there. The Miocene ecosystem was recovering from the ‘Oligocene drowning’ a few million years earlier, when up to 80% of the current land area of New Zealand was submerged. The wildlife that lived in, on, and around the palaeolake Manuherikia was uniquely New Zealand, which strongly suggesting that some emergent land remained during this near drowning event. Marked global cooling and drying during the Miocene, Pliocene and the Pleistocene Ice Ages resulted in the extinction of the ‘subtropical’ elements of the St Bathans’ fauna. Those that survived adapted to the dynamic geological and climatic changes, and would form part of the enigmatic fauna that characterised New Zealand when humans arrived in the late 13th century.

Stout-legged wren

The stout-legged wren or Yaldwin's wren (Pachyplichas yaldwyni) is an extinct species of New Zealand wren, a family of small birds endemic to New Zealand.

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