New Zealand wren

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 hybridisation study, suggested the family was a sister taxon to the suboscines 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), 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 million years ago, 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 at that time. New Zealand's minimum distance from Australia is a bit more today – some – whereas it is now at least 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. The earliest known fossil is Kuiornis indicator from the Early Miocene St Bathans fauna. Kuiornis is thought to be more closely related to Acanthisitta than to other Acanthisittids. The relationships between genera and species were formerly 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. The final genus was Dendroscansor, which had one species, the long-billed wren. A mitochondrial DNA study in 2016 resolved much of the phylogeny, though the placement of Dendroscansor was unresolved due to lack of DNA testing due to the rarity of its remains. It was found that Xenicus was paraphyletic with respect to Pachyplichas, and that the stout legged wrens must have evolved from a gracile-legged ancestor, and the paper suggested placing the Pachyplichas species within Xenicus. It was also found that the split between Lyall's wren and other acanthisittids probably took place during the Oligocene, over 30 million years ago, so acanthisittids must have survived the Oligocene drowning. A cladogram is given below: • †Lyall's wren, Traversia lyalli • Genus Acanthisitta • Rifleman, Acanthisitta chloris • Genus Xenicus • †Bushwren, Xenicus longipes • New Zealand rock wren, Xenicus gilviventris • †North Island stout-legged wren, Xenicus jagmi (possibly conspecific with Xenicus yaldwyni) • †South Island stout-legged wren, Xenicus yaldwyni • Genus †Dendroscansor • †Long-billed wren (New Zealand), Dendroscansor decurvirostris Fossil genus and species †Kuiornis indicator from the Early Miocene St Bathans fauna ==Description==

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 ranges 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; 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. 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 1280 CE), they had a widespread distribution across both the North and South Islands and on Stewart Island. 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. Currently, the New Zealand rock wren is confined to alpine and subalpine zones (900–2500 m altitude) on the South Island. It is possible that the species was once present in the North Island, although this has never been proven. Lyall's wren was once thought to have been restricted to the tiny Stephens Island in Cook Strait, but fossil evidence has shown the species was once widespread in both the North and South Islands. 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. 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. ==References==