Rock wrens/tuke live year-round in the harsh alpine environment. No bigger than a silvereye, they are weak flyers and nest on the ground, making them easy prey for rats and stoats.
The Department of Conservation (DOC) began monitoring rock wrens at 22 sites from Fiordland to Kahurangi in 2019 to measure how populations respond to predator control. Two summer surveys have been completed.
DOC lead researcher Tristan Rawlence says results are showing healthy rock wren/tuke populations largely where predators are managed.
"For the first time we're getting an overall picture of how rock wrens are doing and it's looking good where predators are controlled, but dire where they're not.
"We're seeing good numbers of rock wrens at the 12 sites under predator control using aerial 1080 and traps, mostly in the southern South Island.
"They are also doing well at sites in Westland where there is podocarp and hardwood forest, rather than beech, and different predator dynamics at play.
"In the northern South Island, we found fewer birds and none at sites north of Lewis Pass in the Spencer Mountains and Victoria Range where they were previously," says Tristan Rawlence.
The healthiest rock wren populations were found in the upper Hollyford valley, Harris Saddle on the Routeburn Track, Haast Range, and several sites in Westland located between the Taramakau and Paringa rivers.
Smaller numbers of rock wrens/tuke were counted in Kahurangi National Park where it seems the 2019 mega beech mast and resulting stoat plague may have had an impact on the population there, despite widespread predator control.
At each monitoring site field researchers walk along a series of fixed lines (each 250 m) counting all rock wrens/tuke seen and heard. It sounds easy but the small birds are hard to spot among the rocks and have a high-pitched call, which can be difficult to hear.
DOC tested this survey method against other standard bird monitoring methods in a study on rock wrens from 2012–2018, which was published in the international journal PLOS ONE. It was important to validate this new method for rock wrens to ensure monitoring was scientifically robust.
Community groups and other organisations are also contributing to rock wren/tuke surveying in some areas, such as the Matukituki Charitable Trust and Aspiring Biodiversity Trust in Mount Aspiring National Park, Te Manahuna Aoraki in Aoraki/Mount Cook National Park and Friends of Cobb in Kahurangi National Park.
Air New Zealand provides DOC with sustained pest trapping and species monitoring support across six Great Walks, including 10,347 ha in the Routeburn, which provides benefit to a range of native species, including rock wrens.
The rock wren/tuke monitoring is part of DOC's Tiakina Ngā Manu predator control programme. Results will inform future predator management for recovery of this species and track population trends over time.
DOC rock wren/tuke monitoring sites 2021 – map (PNG, 621K)
Background information
Rock wrens/tuke are New Zealand's only true alpine bird. Northern and southern populations have been found to be genetically distinct with the northern birds assessed as more threatened than the southern ones.
It was once assumed this species was relatively safe from predators in their alpine habitat. However they have declined in many areas they were once commonly found. Researchers using nest cameras found rats and stoats were the main predators.
DOC has previously undertaken intensive studies on the effects of predator control (using aerial 1080 and/or traps) on rock wrens at several different sites, which show they strongly benefit with more adults and chicks surviving compared to areas with no predator management.
Rock wrens/tuke have also been harnessed with tiny radio transmitters to study survival through a 1080 operation, and none were poisoned.
Tiakina Ngā Manu is DOC's national programme to protect taonga native species and forests through predator control as part of Predator Free 2050.
