New Zealand Wrens (Acanthisittidae)
New Zealand wrens
Suborder Tyranni (Suboscines)
Small, compact, superficially wren-like birds occupying the ecological niches of small rodents and insectivores
3–4 in (8–10) cm
Number of genera, species
2 genera, 4 species
Forest, scrubland, alpine
Of the four species known in historic times, two are extinct, and two are still fairly common and fully protected by law
Endemic to North and South Islands, and some satellite islands, of New Zealand
Evolution and systematics
New Zealand wrens have nothing in common with the more familiar wrens, Northern Hemisphere birds of the family Troglodytidae. Visible similarities between the families are superficial. DNA comparison and morphological studies strongly suggest that the Acanthisittidae are living relatives of the earliest passeriform birds, which date back at least 85 million years, when New Zealand severed from West Antarctica during the later stages of the Gondwana supercontinent breakup. Nevertheless, placing them in the oscine (Passeres) or suboscine (Tyranni) passerine suborders, or perhaps in a suborder all their own, is an unsettled issue.
The Acanthisittidae show a mix of oscine and suboscine traits. The syrinx (a vocal organ in the throat) differs in anatomy and position in the body from that of a typical oscine syrinx. On the other hand, the Acanthisittidae lack typical suboscine inflated stapes (a bone in the inner ear). The stapes are unique and more like oscine stapes. DNA hybridization studies among New Zealand wrens and 10 other passerine bird species by Sibley and Ahlquist (1990) showed the greatest similarity of New Zealand wrens with an oscine (bowerbird [Ptilonorhynchidae]), and the least with one Oldand one New-World suboscine, respectively (pitta [Pittidae] and tyrannt flycatcher [Tyrannidae]).
Acanthisittidae is divided into two genera that are living or recently extinct (Acanthisitta, Xenicus), and another two that were extinct before historical times (Dendroscansor, Pachyplichas).
Genus Acanthisitta is monotypic with only one species, the rifleman (Acanthisitta chloris).
Genus Xenicus includes three species: one living (rock wren [Xenicus gilviventris]) and two recently extinct (bush wren [Xenicus longipes], Stephens Island wren [Xenicus lyalli]).
The rock wren survives in the highlands of South Island. The bush wren is probably extinct; none have been seen since 1972. The extinct Stephens Island wren is probably the most generally well known of the New Zealand wrens, due to ironic circumstances of its habitat, discovery, and demise.
Three fossil species, known from the Holocene of New Zealand, have been found: Pachyplichas yaldwyni (Millener, 1988), Pachyplichas jagmi (Millener, 1988), and Dendroscansor decurvirostris (Millener and Worthy, 1991).
New Zealand wrens are among the smallest of birds, at 3–4 in (8–10 cm), so compactly built and short-tailed that at rest they may look truncated or almost spherical. They have short wings and stout legs with strong, gripping feet. The toes are long and slender, and the third and fourth toes are joined at their bases. The bill is straight or slightly upturned, slender, and pointed. Coloring among the Acanthisittidae runs to greens, browns, and white.
As a family, New Zealand wrens are—or were in historical times—common throughout the two main islands of New Zealand and several satellite islands. Today, the rifleman (Acanthisitta chloris) is still fairly common in forest and scrub on both main islands. The rock wren (Xenicus gilviventris) is somewhat less common on South Island, inhabiting rocky areas and alpine scrub at or above timberline in mountainous areas from Nelson to Fiordland.
The living Acanthisittidae are well adapted to forest, scrubland, and alpine environments, all of which are likely to harbor abundant larders of insects, the wrens' main food source.
Behavior among Acanthisittidae species has often been likened to that of small rodents and insectivores like mice or shrews, and they may fill niches of small feeders on New Zealand that, until historic times, had no such indigenous mammal types.
Feeding ecology and diet
Typically, an individual, a bonded male and female couple, or a family group forages on the ground or crawls over the bark and within the leafy parts of trees to search for, snag, and eat small arthropods.
Breeding season is November–March. Males and females form strong, long-lasting monogamous pair bonds. Both construct the elaborate nest—riflemen in tree crevices, rock wrens in rock crevices. Males feed nesting females and both parents feed chicks.
Of four species known in historic times, two have been exterminated by introduced domestic cats, stoats, ferrets, weasels, and rats. The Pacific Island rat was brought to New Zealand by colonizing Maori many centuries ago, the black rat and Norway rat were brought later by colonizing Europeans.
The bush wren or matuhi, a 4-in (9-cm) forest insectivore, was formerly widespread throughout North, South, and Stewart Islands. The last population lived on rat-free Big South Cape Island (near Stewart Island, off the southeast coast of South Island) until Norway rats jumped ship onto the island in 1961 and subsequently exterminated the bush wren. None have been seen anywhere since 1972.
The Stephens Island wren was endemic to the tiny islet between North and South Islands. The entire population was exterminated by a single cat.
The rifleman and rock wren are still fairly common, protected by New Zealand law and a vigorous conservation program. Neither are included in the 2000 IUCN Red List of Threatened Species, but the rock wren is listed as threatened by the New Zealand Department of Conservation.
Significance to humans
List of SpeciesRifleman
Stephens Island wren
Acanthisitta chloris Sparrman, 1787.
other common names
French: Xénique grimpeur; German: Grenadier; Spanish: Reyezuelo de Nueva Zelanda Fusil.
The riflemen, the smallest living bird species in New Zealand, averages about 3 in (8 cm). There is considerable sexual dichromatism and dimorphism. The female is larger than the male, an odd reversal of the normal state of affairs in bird life. Male dorsal parts are bright yellow-green above; female dorsal parts are striped darker and lighter brown and riddled with red-brown flecks. Both sexes have white ventral parts, white superciliary streaks, and yellowish rumps and flanks. The wings each sport a yellow bar and a white spot posterior to the bar. Bills of both sexes are slightly upturned, the female's a little more emphatically.
The rifleman is the most cosmopolitan of Acanthisittidae, fairly common and at home throughout most of lowland New Zealand, including the lower two-thirds of North Island, all of South Island, Stewart Island (off the southeast coast of South Island), and the Great Barrier and Little Barrier Islands.
Some ornithologists recognize two subspecies—South Island rifleman (Acanthisitta chloris chloris) and North Island rifleman (Acanthisitta chloris granti)—although the two differ only slightly in color, granti trading chloris's yellow rump for a greenish one.
The rifleman thrives easily in various habitats, including forests, farmlands, disturbed and regenerating habitats, and scrublands. It has even adapted well to landscapes partly composed of non-native plant species.
Riflemen are lively, diurnal birds. The call is a sharp, high-pitched, cricket-like zipt, single or in a rapid staccato. Birds spend their days foraging in trees, winging from one to another, usually over an accustomed route, and only rarely on the ground. A rifleman sometimes displays an odd behavior that Acanthisittidae alone may claim as theirs: an individual will perch on a branch and energetically flick its wings, as if showing off.
feeding ecology and diet
Sexual dichromatism relates to feeding methods. Both sexes feed on insects, spiders, and other small invertebrates, but they split up feeding strategies. The male gleans from the leaves of a tree while the female works the bark, both going about their work meticulously and minutely. Thus, either sex has proper camouflage for its particular gleaning grounds. The female's slightly more upcurved bill may give her an advantage in poking into and prying at loose bark.
Male and female form strong, long-lasting pair bonds. Pairs breed August–January; females lay 2–4 white eggs. A typical pair builds a rather elaborate nest in a tree crevice, sometimes with a dome-like roof, floored and wallpapered inside with spider webs and mosses. The male feeds the brooding female and both parents feed chicks. A bonded pair typically fledge two broods in one season, fledged chicks of the first brood often pitching in to help feed chicks of the later brood.
The species is widespread, fairly common, and protected by law. It is not threatened.
significance to humans
Stephens Island wren
Xenicus lyalli Rothschild, 1894.
other common names
English: Stephens wren; French: Xénique de Stephen; German: Stephenschlüpfer; Spanish: Reyezuelo de Stephen.
A typical individual was 4 in (10 cm). Both sexes were colored similarly, the female being merely duller. Both had small but
stout, strong bills. The lower mandible was light brown, as were legs and feet, the upper mandible dark brown with a horn-colored tip. The tail was little more than a stub. Although the overall body color was brown, the superciliary streak, chin, and throat were greenish yellow. Light-brown feather margins on partly overlapping body feathers decorated male and female with rows of roundish, fuzzy-edged spots on a darker brown backround. Rows, parallel to one another while following body contours, ran head to tail and covered the entire body, lending the birds a passing resemblance to pinecones. The female's spots were more softly applied.
The species inhabited only this small island, a mere 100 ft (30.5 m) square, but steep-sided, with an elaborate ecology.
Steep, rocky outcroppings; a small forest, grass, and scrub.
All that is known about this species, including its behavior, was recorded by a single person, George Lyell. The birds ran and skittered about on the ground, similar to mice, whose niche the birds likely filled. The species could not fly, or flew very little and ineffectively—a handy adaptation to life on a very small island, but marking them for certain death from introduced predators. The short, rounded wings and soft plumage attest as well to diminished or lost powers of flight. The voice was never described.
feeding ecology and diet
The wrens were apparently most active during twilight hours and may have been nocturnal. They would emerge from holes in rocks and spend some time poking about, alternately running about and hiding, most likely hunting for small arthropods.
The Stephens Island wren is emphatically extinct. Its discovery and extirpation are a masterpiece of cruel irony. The birds went unnoticed and were safe until the New Zealand government built a lighthouse on the islet and in 1894 staffed it with George Lyell, who brought his cat, Tibbet, to the island with him. The consequences are predictable. Within a few months, Tibbet killed, then ate or brought home as show-off gifts for his master, the entire population of Stephens Island wrens. Lyell sent nine corpora to prominent ornithologists Walter Lawry Buller and Walter Rothschild, who declared them a previously unknown species of New Zealand wren. By the time the glad news reached Lyall, the wrens were extinct. As if in a final petulant jest, the birds were scientifically dubbed Traversia lyalli, later changed to Xenicus lyalli, after the owner of the cat who wiped them out. Ten specimens still exist, distributed throughout five museums.
significance to humans
Among biologists and conservationists, the Stephens Island wren has become a poignant symbol of the fragility of isolated island species with limited space and populations.
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Kevin F. Fitzgerald, BS