Acanthisittidae – New Zealand Wrens

The New Zealand wrens Acanthisittidae are a family of very small 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. More recent studies suggest that they form a third (neither oscines or suboscines), 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.

This tiny family has just two extant species, in two genera. Two others have become extinct in modern times. The Stephens Island Wren was a small island endemic and almost flightless. It’s entire, very small, population was extirpated by the lighthouse keeper’s cat on Stephens Island! Once widespread in all three main islands of New Zealand, the near flightless Bushwren was last seen on North Island in 1955, on South Island in 1968 and the Stewart Island’s last survivor of an attempted breeding programme perished in 1972.

New Zealand wrens are mostly insectivorous foragers of New Zealand’s forests, with one species, the New Zealand rockwren, being restricted to alpine areas and only on South Island. Both the remaining species are poor fliers and four of the five extinct species are known to (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 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 fairly 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.

Rock wrens mostly eat invertebrates on the ground, but will sometimes take berries and seeds, and even nectar from flax flowers. Pairs maintain a year-round territory, and work together to build a large enclosed nest with an entrance tunnel. The nest is lined with feathers, often from other species of birds. It is a poor flier, rarely flying more than two metres off the ground or for distances of more than thirty metres. It prefers to hop and run with distinctive bobbing and wing flicks. Its call is three high-pitched notes, and pairs sometimes duet.

Rifleman ♀︎ Acanthisitta chloris – ©digitaltrails CC BY-SA 2.0 via Wikimedia Commons

The Rifleman is insectivorous and searches for maggots and small insects on tree trunks and among leaf litter on the forest floor. It searches for food in a similar way to the treecreeper. The bird begins its search from the base of a tree and climbs up it progressively, spiralling up around the trunk. Upon finishing its search of a particular tree, the bird glides to the foot of a neighbouring tree and begins its search again. This spiralling action, like the rifling of a gun barrel, gave rise to the name. The Rifleman has a range of simple high-pitched calls, the most commonly used call being a squeaky and repetitive zipt. Their calls are partly in the ultrasonic range of frequencies, although it is unknown what function this serves or even if riflemen are able to hear sounds at these frequencies.

They, 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, specifically the Polynesian rat, and are known today only from fossil remains; a third, the Stephens Island wren, became extinct on the main islands, surviving only as a relict population on Stephens Island in the Cook Strait after European settlement. Of the two remaining species, the rifleman is still common on both the North and the South Islands, while the New Zealand rockwren is restricted to the alpine areas of the South Island and is considered vulnerable.