Nature /

Discover New Zealand’s only true alpine bird, the alpine rock wren

The future of New Zealand’s only true alpine bird hangs in the balance, but it’s

hoped a joint predator control project between Te Manahuna Aoraki and a group

of Aoraki/Mount Cook volunteers will provide the lifeline it needs to survive.

regarded as the Sir Edmund Hillary of the bird world, the New Zealand alpine rock wren ( Xenicus gilviventris) defy all laws of survival, spending their entire lives hopping and bobbing in rocky, craggy areas high above the bush line where other birds wouldn’t stand a chance. Confined to remote mountainous regions of the Southern Alps and within the Kahurangi National Park, rock wrens are scarcely hanging on in areas where there is no predator control.

One of just two remaining species of the New Zealand wrens, rock wrens or pīwauwau are one of New Zealand’s smaller birds, weighing between just 14–20 grams, but don’t let their diminutive size fool you for a second. They are high altitude specialists, recorded at elevations of up to 3000 m, where snow lies year-round. ‘They are our little avian mountaineers,’ says Dr Kerry Weston, a science advisor for the Department of Conservation.

‘A weak flier, they have these really big feet which are perfect for rock climbing. They spend a lot of time on the ground, constantly flitting around and searching for food amongst their seemingly barren rocky habitat. They are the only bird species that New Zealand has which are truly alpine, spending their entire life above the tree line.’

Rock wrens eat mainly moths, caterpillars, flies and spiders, although they also eat berries, seeds and even sip the nectar from flax flowers. Breeding takes place over spring and summer with the birds building fully enclosed nests with a small entrance at ground level in cavities within natural features, such as rocks or the base of flax bushes. Both parents share incubation and looking after fledglings.

But just how rock wrens survive winter in the mountains, when the alpine and sub-alpine zone can be covered in snow and ice for many months and temperatures plummet below -10°C, remains a mystery, says Kerry. She suspects the birds go into a kind of hibernation (torpor), lowering their energy requirements, coming out to feed when necessary.

New Zealand once had seven (possibly eight) species of wren – four flightless and three aerially challenged – and now only the rock wren and its cousin the forest rifleman (New Zealand’s smallest bird) remain.

Regrettably, our tiny wrens didn’t fare well once people arrived due to habitat loss and predation. The long-billed wren, with its scimitar-shaped beak for probing into deep crevices, and the North and South Island species of stoutlegged wren, were wiped out in pre-European times, victims of kiore, the Pacific rat.

Next, the Lyall’s wren (initially known as the Stephens Island wren), the smallest flightless bird ever to have existed (weighing about 22 g) fell foul to the lighthouse keeper’s cat after the scientific world heard almost simultaneously of its discovery and subsequent disappearance in the 1890s. There