Fighting them in the beeches

Forest and Bird, Issue 298, 1 November 2000, Page 30

Fighting them in the beeches

—Gordon Ell.

Central river flats, and beech forest, Hurunui South Branch

A ‘mainland island’ project in the Hurunui valleys of North Canterbury is bringing back the birds.

route over the Southern Alps for centuries. Working inland along the shores of Lake Sumner (Hoka Kura), the old greenstone and gold trails followed the North Branch of the Hurunui, over Harper Pass and down to the West Coast, by way of the tumultuous Taramakau. Trampers still take the route but, increasingly in recent years, the people who’ve been heading into the headwaters of the Hurunui have been officers of the Department of Conservation, and volunteers supporting efforts to establish a ‘mainland island’ in the mountains, to save several species from extinction. This is high beech country but the enfolding forests have been modified since the days when Maori traded greenstone and goldminers sought their Eldorado. The wlidlife was largely silenced as introduced pests took their toll of native birds, and even the fabric of the forests. Among the birds at risk are yellowhead (mohua), orange-fronted parakeet, and roroa or great spotted kiwi. There are kaka and kea here too, along with yellowcrowned parakeet, falcon, robin and migratory cuckoo The Hurunui has two main sources, the North and South branches, both falling from the Main Divide. At 12,000 hectares, their upper valleys make up New Zealand’s largest ‘mainland island’. All of the protection work has so far concentrated on the South Branch, where intensive trapping and poisoning of pests began in 1995. The North Branch, which carries the Harper Pass route to Westland, has been used since the summer of 1998-9 as a reference area, to see what happens when nothing is done. ‘The point of this mainland island is to find out how to manage a forest for its entire ecosystem, rather than for individuals within an ecosystem which we tended to do have followed the Harper Pass

in the past, says the DoC scientist who guides the project, Andrew Grant. "We chose the Hurunui partly because of its physical nature — it was possible to isolate the area geographically — and partly because of its outstanding populations of threatened species; mohua, orange-fronted parakeet, kaka and kiwi? The upper Hurunui valleys are clad in deep beech forest protected from the onslaught of West Coast rains by the snowy crests of the Main Divide. The trees are a mixture of silver, red and mountain beech. Their valley floors are carpeted in short tussock and river-flat herbfield, along with wetlands which are ‘suprisingly natural and representative. The alpine area, above the bushline, has snow tussock and alpine herbfields. As one of the ‘most intact’ beech forests left in Canterbury, the upper Hurunui is managed to restore habitat damaged by red deer, chamois, possums, hares, and roaming farm stock. Wildlife is further protected in the South Branch by the poisoning of stoats and possums which attack both birds and their nests. To date, rats and cats have not been particularly apparent but the DoC guardians are ever watchful lest the eradication of one species leads to an increase in another. As a ‘mainland island’ the Hurunui river valleys fit into a national strategy of the Department of Conservation — to somehow ‘ring fence’ an area of mainland habitat, attempt to remove the pests, and stop them from reinvading from the surrounding countryside. The concept requires an

area which can be isolated by geography or fencing. In the Hurunui it is hoped the mountain ridge tops will form part of the boundaries. Electric fences across the valley floors are erected to keep cattle and sheep out. ‘It’s possible for possums to cross the ridges from one valley to the other but we think invasion comes at the forest edges along the valley floor, says Andrew Grant. ‘For this reason we concentrate our work on poison-bait lines laid along the lower forest fringes. In the summer breeding season, teams of

three DoC staff spend 10 days at a time stationed in the South Branch, to carry out the poisoning work. (They also monitor bird populations and gather other data to judge the effect of their work.) Pest control is the critical factor in creating a ‘mainland island’, with poison bait stations defending the borders. To get control of pests, the island’s managers first set bait-lines for possums and stoats along the forest edge of the South Branch valley. The bait-line, surrounding the valley floor, is around 27 kilometres long. The bait stations are established some 100 metres apart, along the bush fringes of the river flats: 158 are baited with 1080 in pollard for possums; 222 are baited with 1080-injected eggs, 50 dozen at a time, to poison stoats. ‘The programme is an experiment to find a cost-effective way to control pests in a val-ley-based beech forest, says Andrew Grant. In the South Branch of the Hurunui bird populations appear to be responding to the special treatment. Populations of the 33 different native bird species are growing. Among the birds being studied is the great spotted kiwi, a South Island species now largely restricted to three regions of forested mountain country: in the Kahurangi National Park of northwest Nelson, the Paparoa Ranges, and the forests of the Hurunui high-country and adjoining Arthurs Pass National Park. Nocturnal and shy, they are less studied than New Zealand’s other kiwi species but may be just

as vulnerable to the onslaught of introduced pests, a focus for research. Besides poisoning pests to protect nesting birds, conservation workers have captured 22 great spotted kiwi in the North Branch forest and banded them for study. Yellowhead populations are recovering with stoat control. This despite what managers call a ‘mast’ season, when beech trees carry exceptional quantities of seed — boosting mice, and consequently stoat populations. This last summer, stoat-poisoning protected the yellowheads with few chicks lost to stoats. Numbers of the birds have increased to between 150 and 200 along the South Branch and between 50 and 75 in the North Branch. A sub-section of the yellowhead population — 25 birds — is closely watched through the breeding season. In 1997-98, nine of 10 banded birds succeeded in raising young, indicating the effectiveness of stoat control. ‘There appears to be a positive response to the methods we are using both for birds and vulnerable plants; says Andrew Grant "but we can't tell yet, whether this is the result of management, or some combination of management with the very unusual beechmast cycle and abnormal weather patterns. (See diagram.) The South Hurunui valley also holds the only significant population of an endangered kakariki. The orange-fronted para-

keet is distinguished from the yellowcrowned parakeet by an orange ‘front’ rather than a red band above its bill, and orange rather than red rump spots. Over the years, arguments whether it is some kind of hybrid between red and yellowcrowned kakariki have abounded: more recently it was accepted that orange-fronted parakeets are a colour phase of the yellowcrowned parakeet (just as, in the South Island, some fantails appear in a black phase while being of the same species as the pied fantail). Now, according to the Department of Conservation, DNA tests have deter-

mined the orange-fronted parakeet is actually a separate species (see Conservation Briefs, page 6). Highly endangered and geographically limited, the estimated population of 150-500 birds is restricted to the South Branch of the Hurunui, and a small population in the Hawdon Valley of nearby Arthurs Pass National Park. Their survival is understandably a focus for pest control work; the birds have always had a category A rating in the priorities for threatened species protection. At the same time, other native species benefit as the tide of introduced pests is driven back to the shores of the mainland island. Among these are plants: the scarlet bloom of mistletoes which grow on the southern beeches have reappeared in the area where possums are controlled. Most beech forests have already lost these ‘icecream’ plants to these introduced browsing animals. The summer flowers are a visual reinforcement of what the ear indicates; renewed birdsong in the South Branch indicates a turning of the tide of recovery in the cool valleys of this

mainland island.

North versus South Hurunui esearch into methods of pest control and bird numbers began in the North Branch of the Hurunui in the summer of 1998-9. According to Andrew Grant, the Department of Conservation scientist responsible, this work provides a comparison with methods used in the South Branch since 1995. "This is largely monitoring work, but eventually we’d like to do pest control in the North Branch too, he says. ‘Presently we maintain bait stations in the North Branch but without poison. This gives us an idea how pests use bait stations. An electric fence has been erected across the valley floor just below the Hurunui Number 3 Hut to keep out grazing farmstock. Already this has produced an improvement in native-plant habitat, as swampy areas are no longer pugged by cattle. ‘We have also introduced "exclosure plots" where we can measure the effect of protection from deer, chamois and farmstock’ Some exclosure plots are also designed to measure the effect that hares have on regenerating plants. The Hurunui experiments also include measuring again in plots first fenced off by the old Forest Service in the days of the Lake Sumner Forest Park. Native broom is recovering inside the protected areas. At the same time bird studies are carried out, listening for calls at five-minute intervals, and checking on banded birds. The North Branch carries a good population of yellowhead too. Both kiwi and possum are tracked with radio-telemetry to establish their movements and behaviour. Other research in the mainland island generally, includes keeping a record of beech-seed falls, mouse and hare populations, and sampling gut material from possums to trace what foods they favour. ‘All this information should help us gain knowledge and improve methods for restoring beech forests, Andrew Grant says.