Alpine predator control for the endangered rock wren Xenicus gilviventris

Rock wren protection installation

Classified as nationally endangered, the rock wren (Xenicus gilviventris) is New Zealand’s only true alpine specialist remaining in the mountains above the treeline for most of its life.  Following the results of ABT’s rock wren survey transect monitoring during Jan/Feb 2018 the team have been installing invasive mammal predator control within two key focal alpine areas. Areas include, the Crucible basin within the Siberia Valley and the upper Lucidus/ Lake Castalia, North Branch of the Wilkin.

Approach to upper Lucidus/ Castalia to deploy invasive mammal traps. Pilot Blair Backcountry Helicopters and Ecologist Rachel Hufton.

Invasive mammalian predator traps (DOC 200 and 150 models) were transported in to both sites on a suspended sling from a Hughes 500 helicopter. The traps were then distributed to designated locations extending and complementing existing predator control efforts within the locality.

Crucible basin rock wren protection deployment with Makarora’s Backcountry Helicopters

Site locations within the Makarora Catchment can be seen from the topograph image below. The North branch of the Wilkin and the Crucible basin are situated to the west of the Makarora River.

Population status

Rock wren are at risk from invasive mammalian predation particularly from stoats and rats but also mice. There is increasing recognition that invasive predators are widespread within New Zealand alpine zones. Recent work has found that humane kill trapping of invasive predators can increase rock wren breeding success within the alpine environment (Weston et al 2018).

The national population of rock wren is currently unknown but thought to be around 5,000 mature individuals (IUCN) with severely fragmented populations due to particular habitat requirements. The rock wren belongs to a unique ancient lineage of eight New Zealand wrens now only two species survive. The alpine rock wren and the rifleman Acanthisitta chloris, generally a forest passserine.

Male rock wren upper Lucidus/ Castallia

During both trips it was encouraging to observe a number of adult rock wren present busy foraging on invertebrate prey. Particularly, at Crucible basin following the late November snowfall. Most birds were male which may indicate females occupied on their nest sites.

Remote trap monitoring

With the aim of optimising alpine trap servicing efficiency and improving understanding of temporal and climate influences on predator trapping ABT have partnered with Encounter Solutions Ltd to install remote trap monitoring technology. The equipment will be installed in January for both alpine sites. This system has been applied to other trapping habitats but will be a first for the alpine environment.  If successful other remote rock wren habitats could benefit from use of this technology to aid predator control programmes.

Rock wren protection installation at Crucible Basin, Andrew Shepherd helping to distribute kea proof traps.
ABT’s Anthony Coote securing and geo-referencing mammalian predator traps at Lake Castalia.

Future populations

With dedicated effort it is possible that focused rock wren recovery at these sites could result in potential “source” populations of rock wren and expansion/ migration of numbers/ pairs into unoccupied habitat (Weston 2014).

With thanks to Otago Community TrustOtago Regional Council, Oceana Gold, Backcountry Helicopters Ltd, Tony Zimmerman trap supplies, Central Otago Hunting and Fishing, DOC Wanaka, Backcountry Saddles Expeditions, volunteers Nick Beckwith and Andrew Shepherd.

References

Aspiring Biodiversity Trust (2018). Alpine predator control plan for rock wren. Makarora Catchment Threatened Species Plan.

IUCN Red List of threatened species

Weston K.A. 2014. Conservation genetics of alpine rock wren (Xenicus gilviventris). Doctorate thesis.

Weston K.A., O’Donnell C.F.J., Van Dam Bates P. & Monks J.M. 2018. Control of invasive predators improves breeding success of an endangered alpine passerine.

Male rock wren Crucible Basin (Nov 2018).

Endangered bird life of the Crucible Basin, Siberia Valley

ABT’s rock wren transect survey monitoring programme for the 2017/2018 survey season includes the Crucible Basin situated within the Siberia Valley. Monitoring surveys aim to provide an updated baseline on threatened species and allow repeatable monitoring for rock wren within the Makarora catchment to help guide appropriate future conservation management in relation to invasive mammalian predators.

Kea (juvenile male) at Lake Crucible looking towards the Gillespie Pass, Makarora

A number of rock wren pairs were recorded present within the bolder-field and moraine habitat and evidence of adults foraging invertebrates for nestlings was noted. During rock wren surveys the Crucible Basin was also noted as an important site for kea as well as rock wren. On both survey occasions seven kea were observed, mainly this years juveniles with their characteristic yellow ceres, eyelids and pale crowns. Kea parents were observed feeding young fledglings regurgitated food and a rock bivi frequented by kea was found close to Lake Crucible.

A pair of rock wren below photographed during their diagnostic bouncing display on their long legs with occasional emissions of characteristic sharp tweet calls http://nzbirdsonline.org.nz/species/rock-wren#bird-sounds.

Male rock wren
Female rock wren

ABT are collaborating with DoC to extend current mammalian trapping efforts for rock wren within the alpine environment of the Makarora catchment.

Kea fledgling (2017/ 2018) Lake Crucible

All kea records in relation to ABT’s survey and monitoring have been forwarded to the Kea Conservation Trust to help inform a national kea database.

Generally our time at Crucible Basin was positive however, we did note an aerial drone trying to film kea and artificial feeding by visitors. These are two national issues where continued awareness raising is crucial for New Zealand’s threatened species. Image below shows a hunkered down kea looking up at the drone buzzing above whilst others disappeared beneath boulder habitat.

Young kea looking up at overhead drone – Lake Crucible

Confirmed presence of a rock wren colony….

Rock wren of the Wilkin Valley

The Aspiring Biodiversity Trust are pleased to report the confirmed presence of rock wren at the north branch of the Wilkin River following the undertaking and setting up of a recent (Jan 2018) transect monitoring survey.

rock wren - Rachel Hufton
Rock wren (adult female)

Rock wren Xenicus gilviventris is the only true alpine New Zealand bird species and is currently classed as globally endangered under the International Union for the Conservation of Nature (IUCN). Peter Child’s (1980) work was the first comprehensive bird survey of Mt Aspiring National Park for rock wren.

Rachel Hufton rock wren survey
Rachel Hufton surveying rock wren habitat at Lake Castalia, north source of the Wilkin River.

The main threat to this species is predation from invasive mammals such as stoats and rats now known to be present within alpine environments. The results of the survey will help inform and guide existing and future conservation management for rock wren. Monitoring transects will also be repeated in subsequent years to allow more informed decisions to be made in relation to this indigenous alpine specialist.