26 September 2024

New data shows numbers of rock wren/pīwauwau/tuke, Aotearoa New Zealand’s only true alpine bird, are increasing where predators are controlled in its mountain home.

The Department of Conservation has monitored rock wrens across the South Island for the past five years to see how they fare both with and without predator control using methods like trapping and aerial 1080.

DOC Science Advisor Tristan Rawlence says monitoring shows rock wren numbers are mostly increasing where predators are regularly controlled but gradually declining at unmanaged sites.

“On average, there are more than double the number of rock wrens in areas with predator control compared to areas without,” says Tristan.

“Stoats can be common in alpine areas and we’re increasingly seeing rats in this environment too, possibly due to warmer temperatures.”

Rock wrens hop and flit rather than flying and nest on the ground, making them easy prey for introduced predators like rats and stoats. They are threatened with extinction.

With five years of monitoring data, Tristan says it’s now possible to see which predator control methods are of most benefit to rock wren.

“We’re seeing the best results where we’re using aerial 1080 in the alpine area above the tree line where rock wrens live year-round, and not just in the surrounding forest.

“We’ve also learnt we need to control predators whenever the beech forest seeds, as predator numbers soar in response to more food.”

Rock wrens live in alpine areas in the Southern Alps/Kā Tiritiri o Te Moana and Kahurangi. They can go into torpor or semi-hibernation (dropping their body temperature and energy needs), an adaptation thought to help them survive harsh winter conditions.

Each summer since 2019, DOC researchers have surveyed for rock wrens at 25 sites ranging from Fiordland to Kahurangi. There are 19 monitoring sites where rock wrens are protected through predator control and six sites where there is no management. Monitoring frequency has now been reduced with sites visited every two years.

Previous research has shown rock wrens produce 3-5 times as many chicks when predators are controlled. A study in Kahurangi National Park over four years showed 58% of rock wren nests were successful in fledging young following aerial 1080 predator control, while just 13% were successful without.

This monitoring programme is part of DOC’s National Predator Control Programme, which protects the most at-risk wildlife and forests across New Zealand’s public conservation land.

Rock wrens belong to an ancient lineage of New Zealand wrens that once included seven species. Today, only the rock wren and rifleman/titipounamu survive.

Background information

Rock wren populations found in northern and southern areas of the South Island have been found to be genetically distinct. The northern birds are assessed as more threatened (classified ‘Nationally Critical’ under the New Zealand Threat Classification System) than the southern ones (classified ‘Nationally Endangered’).

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