Justification of Red List Category
This species has a small and fragmented population which is estimated to be undergoing a decline owing to heavy nest predation. It is therefore considered Endangered.
The population is estimated to number 2,500-9,999 mature individuals. This equates to 3,750-14,999 individuals, rounded here to 3,500-15,000 individuals (R. Hitchmough in litt. 2005).
In 2005, 20% of known localities had had no sightings in the past 20 years (P. Gaze per R. Hitchmough in litt. 2005).
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). It was described as locally common (Heather and Robertson 1997), but its distribution is fragmented, and a recent analysis of sightings indicates that about 20% of known localities have had no sightings in the past 20 years (P. Gaze per R. Hitchmough in litt. 2005). Its population is estimated to number fewer than 10,000 individuals (R. Hitchmough in litt. 2005). Its range continues to decline (Michelsen-Heath and Gaze in press) and a 40% decline in abundance over a 20-year period occurred in the Murchison mountains (Willians 2007).
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, house mice Mus musculus and stoats Mustela erminea. It is likely that predation rates vary significantly from year to year (Gaze 2013), and predation may be particularly high in years when M. erminea populations are high in response to mouse plagues (R. Hay in litt. 1999). The only study on nesting in this species showed significant levels of egg and chick loss to mice and stoat (Michelsen-Heath 1989). A number of recent unpublished studies led by the New Zealand Department of Conservation have observed extremely high (80-100%) nest failure due to predation (DOC, unpublished data per Weston 2014, Webb 2015). 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
In January 2005, the Department of Conservation relocated 24 individuals from the Murchison Mountains to predator-free Anchor Island in Dusky Sound. Monitoring of this translocated population has followed (Weston 2006), and a translocation to Secretary Island was planned for 2008.
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
Harding, M., Stringer, C., Khwaja, N., Benstead, P., Mahood, S., McClellan, R., Westrip, J., Taylor, J.
Hitchmough, R., Gaze, P., Hay, R.
BirdLife International (2021) Species factsheet: Xenicus gilviventris. Downloaded from http://www.birdlife.org on 22/01/2021. Recommended citation for factsheets for more than one species: BirdLife International (2021) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/01/2021.