South Island wren  (Xenicus gilviventris)

Classified as Vulnerable (VU) on the IUCN Red List 2006 (1).

The South Island wren is a small but robust alpine bird with a very short tail, rounded wings, and long legs and toes (2) (3). While the male’s plumage is a dull green colour above, grey-brown below and yellow on the flanks, the female is more olive-brown in colour. This charming bird has an unusual habit of vigorously bobbing up and down (3).

As its common name implies, the South Island wren is endemic to the South Island of New Zealand, although it was formerly also found in the North Island before European colonisation. Fragmented populations now remain only in the South Island, from north-west Nelson, down through Westland and the Southern Alps, to Fiordland (3).

The South Island wren is the only ‘true’ alpine bird in New Zealand, both living and breeding in alpine and subalpine habitat all year round (3) (4). This species inhabits the rocky slopes of mountains and valleys above the timberline, between 920 m and 2,900 m above sea level, which are usually vegetated only with alpine and subalpine low shrublands. Nests are built among loose rock or debris, or on rocky ledges, always close to vegetation (3).

Nests are built with leaves, finely shredded grass and feathers, with feathers being laid most thickly on the bottom of the nest, creating a comfortable cushion for the chicks. The reproductive biology of this bird is poorly understood, but pairs are known to breed between October and February, and both parents are thought to care for and feed the growing chicks (2).

The South Island wren is primarily insectivorous, feeding on creatures such as moths, grasshoppers, spiders and worms, but will also occasionally take fruits and seeds from alpine vegetation (2) (3).

Like so many of New Zealand’s native birds, the small and fragmented population of South Island wrens is suffering from nest predation by introduced mammals, and is consequently thought to be under serious decline. A study of the species showed significant levels of egg and chick loss to house mice (Mus musculus) and stoats (Mustela erminea). This small bird is particularly vulnerable in years of high stoat numbers due to periodic mouse plagues, which provide additional food for stoats, allowing their populations to multiply (3).

In January 2005, the New Zealand Department of Conservation relocated 24 South Island wrens from the Murchison Mountains to predator-free Anchor Island in Dusky Sound, in an attempt to help ensure the species’ survival. So far the results have been positive, and this additional, relatively secure population serves as a safety measure for the species, should the population on the mainland suffer further declines or even become extinct. Should the relocation of these birds prove to be successful in the long term, this programme may be extended to include relocations to Secretary Island in Doubtful Sound, providing the stoat control scheme planned for the island in 2005 has been successfully completed (4).

View information on this species at the UNEP World Conservation Monitoring Centre.

For more information on the South Island wren see:

• BirdLife International:
  http://www.birdlife.org/datazone/species/index.html?action=SpcHTMDetails.asp&sid=3992&m=0