Author
Ainslie Talbot

Prior Publication
The Press

Copyright
The Press

Introduced predators have taken a devastating toll of native wildlife. Island sanctuaries have provided a refuge for some New Zealand species, but is there any hope for the mainland? Ainslie Talbot reports.

Night closes like a blanket around a little hut high in the Southern Alps. The skyline ridge a thousand metres above the valley is etched into the slowly darkening sky. The beech forest, falling in dark swathes to the valley floor, seems to breathe in a thick silence. The river's flow is the only sound.

This is the south branch of the Hurunui, arguably one of the most isolated and untouched valleys east of the Main Divide. It is deep in the heart of Lake Sumner Forest Park, three hours of back-jolting driving beyond the end of a private farm track. It is a special place for more reasons than its isolation and forest. It is at the heart of the Hurunui Mainland Island, an environmental research project of the Department of Conservation.

The "island" has existed with little recognition for almost five years. It is one of six such projects in New Zealand. The aim is to "bring back the dawn chorus" and learn how predator-control techniques can be applied in similar areas. Instead of spreading 1080 poison from the air, a controlled programme is carried out on the ground.

The Hurunui, control measures have radically reduced the killing machines of the bush - stoats, ferrets, and possums. Since 1995, the project has dominated the lives of a four-person DOC team. Every summer, two or three members go into the south branch valley for 10-stretches to carry out predator control, research the impact on birds and native flora (such as mistletoe), track mice and rat numbers, and examine the density of beech seed.

All this material, and more, is analysed and brought together on a data base, then used to readjust approaches from year to year. At the same time DOC has been using a neighbouring valley - the north branch of the Hurunui, which leads to Harpers Pass, where no predator work is being done yet - as a comparison. "It's very exciting to see how our work in the south branch is definitely having an effect on the wildlife," says Andy Grant. "There's been a decline not only in the number of predators, but also significantly increased bird life - very rare species like great spotted kiwi, mohua/yellowhead, and parakeets.

"We're seeing increasing flocks feeding through the canopy of the forest, just like in the old days, before predators took over." Few people visit the south branch because of access difficulty. Even a casual visitor can see the difference. The bird life is much more prolific than in most forests east of the Main Divide. You can walk into any area of the forest fringe and find a wealth of birds, not just the ubiquitous fantail and bush robin.

Much native bush must have something like this, but it is a sight and sound experienced by few people who go into the back country these days. The DOC team has fenced the area against stock and established a long line of possum and stoat bait stations about 100m apart on both sides of the valley.

These stations are checked every 10 days. Fresh eggs injected with 1080 poison are placed in the 272 stoat stations, while the possum bait stations are topped up with poison pellets. It's a demanding and lengthy job requiring the placement of 50-dozen eggs along both sides of the valley - a total of 27 kilometres.

"We know that stoats and ferrets live on the fringes of the forest," says field manager Wayne King. "They may hunt further up the valley sides, but they tend to come back down to these areas. This is the best place to locate poisoned eggs. "It's a similar situation with possums. There's a lot of movement up and down the valley sides, with both possums and stoats traveling over huge distances. People are amazed a stoat can travel several kilometers in one night alone, and cover an area of 70 hectares in a few days. No wonder they decimate the birds."

Team members have observed things never before scientifically recorded. They've seen stoats jumping from tree to tree, high in the canopy of the beech forest, in their obsessive hunt for fledglings and eggs. Rats are chased up trees by stoats, then jump to the ground from 20m up. Strange diggings have been seen in the forest floor moss. Their cause still undetermined.

In 1995, 210 stoats were poisoned. By 1999, that had been reduced to less than 50. Possum numbers never high in the south branch, have also been cut. "With possums we have not only been trapping but also monitoring their movements through the use of radio transmitters," says Andy Grant. "We have found that they move down from near the tops to the valley floor and vice versa. There may also be movement from other valleys into the south branch."

As stoat numbers have dropped, mohua have increased to an estimated 250 birds, with fledgling rates increased from 1.7 to 2.4 a nest. Great spotted kiwi have been banded in the north branch as a comparison before intensive survey work begins in the south branch.

Stunning bright-red native mistletoe is another sign of a healthy ecosystem. Possums love this parasite, which grows out from the trunks of beech trees. It is a key indicator of how many possums are in the area. Andy Grant points out fresh bunches of mistletoe high up on red beech. He says if the possums were thick on the ground there would be none. Just outside the protective fence at the start of the valley, there is none.

The mainland island team will return to their computers this winter to analyse and the results. Some in the conservation world have questioned whether having mainland islands is in fact an attempt to create something akin to a mainland zoo. But the Canterbury Conservancy's DOC team point to the success of such islands in restoring kaka and other rare birds to much better health and numbers.

"What we are doing here is demonstrating that intelligent, scientifically applied predator control on the ground can work to save and enhance rare and threatened birds like mohua," says Andy Grant. "We're gradually developing a unique data base. This is practical, evidence-based conservation using scientific techniques, not guess work.

"We think it will have long-term application in other areas. What's the alternative? Sitting back and watching very rare species like mohua or great spotted kiwi disappear? I don't think so. I don't believe New Zealanders want that to happen."

That commitment is reflected in the Government's March announcement of New Zealand's Biodiversity Strategy - Our Chance to Turn the Tide - which considers how we can reduce the destruction of our threatened wildlife and its environment over the next 20 years.

Mainland islands, such as the Hurunui's have a high priority in this strategy. Judging by the results so far, they are important islands of hope.

Keywords
Hurunui Mainland Island  mainland island  Biodiversity Strategy  Department of Conservation 

Updated 20/11/2008 4.10AM by PIPI4