South Island Wren Xenicus gilviventris Scientific name definitions

c. 9·5 cm; male 16 g, female 20 g. Small passerine with rounded wings, very short tail , pale supercilium and fine bill; legs and toes long, feet almost half length of body, claws (especially hind claw) long. Male has head and neck dull olive-brown, white supercilium bordered above and below by narrow black stripes, upperparts and wings olive-green, prominent black patch at bend of folded wing, tail dull olive-brown (head and upperside brighter, greener, in S of range); throat whitish, rest of underparts pale grey-brown to creamy or off-white, flanks yellowish (richer yellow in S); bill blackish-brown; feet pale brown. Female is duller and browner above, often duller below. Juvenile differs from adult in having mostly dark grey bill with orange base of lower mandible, darker legs and feet.

Low shrubs , open scree and rockfalls in alpine and subalpine habitats; often in areas with prolonged snow cover. Often near water source, e.g. stream. At 1200–2900 m, usually to 2400 m, i.e. above timber-line; also lower, down to c. 900 m, in subalpine scrub in Fiordland .

Resident. Apparently sedentary; no evidence for suggested movement to lower elevations during severe weather.

Predominantly insectivorous. Takes wide variety of small arthropods, e.g. coleopterans, orthopterans, dipterans, springtails (Collembola), spiders, centipedes (Chilopoda), millipedes (Diplopoda), oligochaetes. Occasionally consumes small seeds and berries; also seen to drink nectar from flowers of New Zealand flax (Phormium). Large prey may be beaten against a hard surface, and if necessary dismembered, before being swallowed. Observed to cache insect food for short periods. Forages mostly in pairs or in small groups of 4–8 birds, sometimes singly. Terrestrial and arboreal. Hops and runs frequently; flies only short distances, bobs vigorously up and down, often with wing-flicking, on alighting. Gleans items from low vegetation, and from crevices between boulders and stones ; readily enters interstitial spaces, and disappears down holes for several minutes; possibly forages beneath snow in austral winter. Occasionally makes aerial sallies after flying or jumping insects. In study in Mt Cook National Park (Fiordland), covering Dec–May, gleaning was commonest technique throughout period; aerial sallying most frequent in Dec–Jan, and most fruit-eating observed in Jan–Mar.

Small repertoire of simple calls, high-pitched and penetrating; main calls a 3-note “tzee-tzit-tzit” and short single “zipt”, less frequently repeated than in Acanthisitta.

Season Sept–Jan. Monogamous; long-term pair-bond. Nest built by both sexes, cigar-shaped or spherical, tiny entrance hole at end or side, mostly of grass with some soft twigs, leaves, bark, fern scales and hair, chamber lined with feathers, sometimes also with soft moss and lichens; placed in cavity in or near ground, e.g. in crevice between rocks, among sturdy roots, or deep in soft clay or mud bank or layer of soft moss. Clutch 2–5 eggs, laid at 2-day intervals; incubation by both sexes, period 18–22 days; both also feed chicks, nestling period 21–26 days; young independent at 2–3 weeks. Of total of 106 eggs in one study, 91 (c. 86%) hatched and 71 (67%) produced fledglings; nests preyed on by stoats (Mustela erminea) and house mice (Mus musculus).

ENDANGERED. Restricted-range species: present in South Island of New Zealand EBA. Has rather fragmented distribution, from NW Nelson S to Fiordland , but uncommon, even in suitable areas. Former presence in North I indicated by Holocene fossil bones. Rare in N of range in Nelson and W Marlborough, but believed to have been more common in the past in Nelson; more widespread and perhaps locally fairly common farther S in Southern Alps. Few data available (1 Robertson, H.A., Dowding, J.E., Elliott, G.P., Hitchmough, R.A., Miskelly, C.M., O’Donnell, C.F., Powlesland, R.G., Sagar, P.M., Scofield, R.P and Taylor, G.A. (2013). Conservation Status of New Zealand Birds, 25612. New Zealand Threat Classification Series, 4. Department of Conservation, Wellington, New Zealand. Close ), but population is roughly estimated 5000 mature individuals and declining BirdLife International (2017) Species factsheet: Xenicus gilviventris. Downloaded from http://www.birdlife.org on 27/04/2017. (2 Michelsen-Heath, S. and Gaze, P. (2007). Changes in abundance and distribution of the rock wren (Xenicus gilviventris) in the South Island, New Zealand. Notornis. 54(2): 71–78. Close , 3 Weston, K.A. and Robertson, B.C. (2015). Population structure within an alpine archipelago: strong signature of past climate change in the New Zealand rock wren (Xenicus gilviventris). Molecular Ecology. 24(18): 4778–4794. Close ). Previously considered Near Threatened, then Vulnerable, it was uplisted to Endangered in 2016. Principal threat is introduced mammalian predators, especially stoat (Mustela erminea) but also house mouse (Mus musculus); possible that former take a fairly high percentage of nestlings, as well as some adults, and probably many eggs taken by mice. Molecular analyses have identified a deep genetic divergence between N and S lineages, and recommend that each lineage be considered for conservation management purposes as a separate evolutionarily significant unit in order to preserve the full genetic variation within the species (3 Weston, K.A. and Robertson, B.C. (2015). Population structure within an alpine archipelago: strong signature of past climate change in the New Zealand rock wren (Xenicus gilviventris). Molecular Ecology. 24(18): 4778–4794. Close ). Climate change is a potential threat that is predicted to have a disproportionate impact on alpine specialists, as populations become increasingly isolated on shrinking montane islands (4 Weston, K.A., Taylor, S.S. and Robertson, B.C. (2016). Identifying populations for management: fine-scale population structure in the New Zealand alpine rock wren (Xenicus gilviventris). Conservation Genetics. 17(3): 691–701. Close ); it will therefore be vital to maintain large-scale natural connectivity among populations to preserve genetic diversity and permit movement into relatively cooler climes (4 Weston, K.A., Taylor, S.S. and Robertson, B.C. (2016). Identifying populations for management: fine-scale population structure in the New Zealand alpine rock wren (Xenicus gilviventris). Conservation Genetics. 17(3): 691–701. Close ).