Data Zone
Justification of Red List category
This species has a small population which is rapidly declining owing to heavy nest predation. It is therefore assessed as Endangered.
Population justification
The population was previously estimated to number 2,500-9,999 mature individuals (R. Hitchmough in litt. 2005). Robertson et al. (2021), assessing the species according to criteria elucidated in Townsend et al. (2008), placed the southern subspecies in the band 1,000-5,000 mature individuals and the northern subspecies in the band 250-1,000. The total population is best estimated to number c.5,000 mature individuals (Gill and Sharpe 2020).
Trend justification
Predation by stoats causes extremely high rates of nest failure and are thought to be causing significant declines (Little et al. 2017). Sightings in Mount Cook National Park have declined markedly since the 1980s and early 1990s (Michelsen-Heath and Gaze 2007). In 2005, at 20% of known localities there were no sightings in the past 20 years (P. Gaze per R. Hitchmough in litt. 2005). Its range continues to decline (Michelsen-Heath and Gaze 2007) and a 40% decline in abundance over a 20-year period occurred in the Murchison mountains (Willians 2007). Since 2012, the species is suspected to have been undergoing steeper declines equivalent to 50-70% in ten years and this is thought to be continuing (Robertson et al. 2013, 2017, 2021).
Xenicus gilviventris is endemic to New Zealand. Once found in the North Island prior to European settlement, it is now restricted to the South Island, where it ranges from north-west Nelson, down through Westland and the Southern Alps, to Fiordland (Heather and Robertson 1997).
Populations are confined to alpine and subalpine habitat, on mountain ranges and in valleys above the timberline, between c.920 m and 2,900 m (mostly 1,200 to 2,400 m). It inhabits rocky slopes, including talus, open scree, glacial moraine and rocky outcrops, usually vegetated with alpine and subalpine low shrublands. It nests among loose rock or debris, on bluffs or rocky ledges, always close to vegetation. It is insectivorous, but will occasionally take fruits and seeds from alpine vegetation (Higgins et al. 2001). Flight is relatively weak, although birds still range over extensive areas of steep mountain terrain (R. Hay in litt. 1999).
The major threat to this species is predation by introduced mammals, particularly stoats Mustela erminea which are the primary predators of rock wrens. Stoats are able access nests on cliffs as well as the ground and primarily prey on chicks (Little et al. 2017). It is likely that predation rates vary significantly from year to year (Gaze 2018), and predation may be particularly high in years when M. erminea populations are high in response to mouse plagues (R. Hay in litt. 1999). Studies have shown significant levels of egg and chick loss to mice and stoat (Michelsen-Heath 1989) and extremely high (80-100%) nest failure (Webb 2015, Weston 2014). In three areas of Fiordland and South Westland, in the absence of predator control, stoats predated 60-80% of nests (O'Donnell 2017). High rates of predation within isolated populations may be contributing to their demographic instability (Weston 2014). There is an additional threat to this species from climate change, especially if warming temperatures make its core habitat more suitable for ship rats – a potential nest predator which is currently absent (Gaze 2013).
Conservation Actions Underway
Predator control has been shown to positively impact rock wren populations (Rawlence 2019, Weston et al. 2018). Survival rate at several sites has improved due to conservation management, estimated at 0.6 in trapped areas and 0.47 in un-trapped areas (Robertson et al. 2021). Birds have been successfully translocated to Anchor Island and Secretary Island which are intensively managed to prevent the introduction of invasive predators.
10 cm. Small alpine bird. Male dull green above, grey-brown below, yellow flanks; female more olive brown; long legs and fine black bill. Similar: None in range. Hints: Has unusual habit of vigorously bobbing up and down. Voice: Three notes, first accentuated.
Text account compilers
Westrip, J.R.S., Vine, J., Stringer, C., Benstead, P., Taylor, J., Khwaja, N., Mahood, S., Harding, M., McClellan, R.
Contributors
Gaze, P., Hay, R. & Hitchmough, R.
Recommended citation
BirdLife International (2024) Species factsheet: New Zealand Rockwren Xenicus gilviventris. Downloaded from
https://datazone.birdlife.org/species/factsheet/new-zealand-rockwren-xenicus-gilviventris on 22/11/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 22/11/2024.