The Vanishing Rock Wren

Forest and Bird, Issue 310, 1 November 2003, Page 22

The Vanishing Rock Wren

CHRIS PETYT

CHRIS PETYT

reports on ain alpine bircl

in trouble:

Alpine tabitat of the rock Wren Henderson Basin beyond Lake Cobb in Kahurangi National Park, northwest Nelson:

ne of New Zealand's ancient birds, which evolved with the moa more than 24 million years ago, is in serious trouble. Fears are held for the survival of the tiny rock wren which lives in the South Island alps. The New Zealand wrens are an ancient family of small, nearly tailless birds, peculiar to New Zealand and with no close affinities to other groups of birds. They are as unique to New Zealand as the moa. Their history in recent times has not been a happy one. The Stephens Island wren was discovered for science by a lighthouse keeper’s cat, which brought in a number of specimens before exterminating it, with the help of professional bird collectors and deforestation. It was only seen alive a few times; it seemed to be semi-nocturnal, was not seen to fly, but scurried around like a mouse. Bush wrens were apparently widely distributed in the North and South Islands when Europeans arrived, but their arboreal habits were no protection against the

introduced rats and stoats. The last recorded sightings were about 1955 in the North, and the 1960s in the South. Stead's bush wren was common on Stewart Island and several outlying islands, but by the 1960s survived only on Big South Cape Island. In 1964 the wreck of a fishing boat allowed ship rats to invade the island, and the desperate transfer the next year of a few remaining birds to a nearby rat-free island was unsuccessful. There remain the rifleman, the smallest of the group, which is apparently holding its own, especially in the South Island, though in reduced numbers, and the rock wren. The rock wren is known mainly by mountaineers and trampers of the alpine tops of the Southern Alps, from northwest Nelson down to Fiordland. Its name is apt as its preferred habitat is areas of jumbled fallen rocks with crevices and airholes, preferably interspersed with subalpine scrub. The birds hop around on and under the rocks, with much bobbing and flicking of the wings, as they search for insects and grubs. A few years ago I heard there was a concentrated population in the Henderson Basin, near the top of the Cobb Valley inland from Takaka in the Kahurangi National Park. I made my way up there a couple of times and managed to see some birds, but not in the numbers I was expecting, so in 1999 I spent a couple of days camping there to try and estimate the numbers. I found three pairs, all with one or two young, and possibly two more pairs; a lot

fewer than the nine pairs plus young and odd birds found in a study by Alison Ballance for the Department of Scientific and Industrial Research in 1989. The next summer I took up a visitor from the North Island and we found a family party soon after entering the basin after walking up from Fenella hut. My companion spotted a stoat within metres of the birds, alerting me to the fact that stoats will range up into the mountains almost to 1600 metres altitude in this case, and were likely responsible for any decline. A small group of local Forest and Birders decided we would try and help the birds. Peter Gaze of the Department of Conservation lent us 14 Fenn traps and boxes and flew them into the basin for us. We made many trips into the basin during the summer of 2000-01, driving past the Cobb reservoir to the end of the road, then

walking a couple of hours up the valley before climbing up steeply through the beech forest and open tops and crossing a small pass into Henderson Basin. Many different people, including children, accompanied us. We trapped a total of eight stoats, and colour-banded eight wrens to try and follow their progress. Five nests were located, all on bluffs and inaccessible to us, which was interesting as in a study in Fiordland most nests could be reached. The nest is usually made of tussocks and grasses in a sheltered crevice, enclosed with an entrance tunnel in the side. It is usually lined with feathers; Guthrie-Smith counted nearly 800 in one nest, including those of kiwi and kakapo. (Perhaps a lack of feathers for insulation is another problem nowadays.) Despite trapping some stoats there were fears that predation was

occurring: we saw no juveniles from the first nest we located and the banded male was never resighted. At another nest young were being fed one morning but nothing was seen at the nest that evening and no young were ever seen. So it seems stoats were still taking their toll, with mice another possible predator at nests. (Rats don’t seem to venture above the bush-line.) The days in the mountains that summer were very special, with a sequence of blooming flowers to delight us as we roamed the basin and mountains. Walking up the valley we'd often see kaka and kakariki, robins, tomtits and falcons, whilst pipits sang over our camp-site. I remember lying in the tent one morning watching a pair of young keas play-fighting just outside. The wrens were often so friendly, popping up right next to one on the rocks, and disappearing just as quickly underneath

them. They were usually heard before being seen; a high-pitched note above the audible range of some humans, but probably easily heard by a hungry stoat. The next summer was a bit of a washout, with bad weather preventing much activity in the mountains, but we caught another four stoats. The start of the 2002-03 summer was pretty bad too, and other commitments meant we didn't get into Henderson as much as we would have liked, but it appeared there were only two pairs of wrens in the basin. One pair was seen with a young bird, but when next found the female was missing and a stoat had been spotted close by. So it appears the population may have dropped from five to two pairs in a couple of years. We appealed for records from the public for the surrounding area but few sightings were notified, and I searched several areas where there’d been records in

the past but with no success. It seems that the rock wren is declining with disturbing rapidity in the Kahurangi National Park at the northern end of its range. Although we feel stoats are the main problem, it is possible that climate change may also be important. The birds stay in the mountains all year round, the generally accepted story being that they feed amongst the rocks and scrub under the snow-cover all winter. Personally I find it hard to believe that they could find enough food this way to keep them active all winter and feel it more likely that they hibernate, or at least go into a state of temporary torpidity, but winter climate change especially could affect them either way. Certainly wrens seem to be in trouble in our area, and it is likely the same is happening further south. DoC has been informed and they are looking at funding for research and management of this species. Would any offshore islands be suitable for them? Are there populations

that could be more easily protected than the one we're trying to study and protect? We feel that something should be done now, before numbers drop too much further.

is a scientific fisheries observer with

MFish, a committee member of Forest and Bird’s Golden Bay branch and, author of a book about Farewell Spit.

here is no official recovery plan for rock wren but its plight concerns Peter Gaze of the Department of Conservation in Nelson. He is presently seeking sponsorship to remove a population of the birds to a pest-free island in Fiordland as an emergency measure pending a wider scientific review. The Department of Conservation classifies rock wren as ‘nationally vulnerable’ which puts it in the ‘acutely threatened’ group of birds at risk. Little scientific work on the decline has been done, however. Once widespread, the rock wren is now confined to the South Island including the Tasman Mountains of northwestern Nelson and the Victoria Range of northern Westland, down both sides of the Southern Alps and on some side ranges to the east, to Fiordland. Over the last few decades their distribution has become patchy and numbers have declined in most areas. Fires and introduced mammalian predators, especially stoats and mice, are major reasons for their decline. "There is good reason to believe the rock wren may be heading toward a very critical situation, says Peter Gaze. "Rock wren are as special to New Zealand birdlife as kiwi, kokako and huia, yet their conservation has been largely ignored’. ‘Prompt intervention to establish rock wren on at least one predator-free island would be an important first step, he says.

Help at Last As we went to press, some cheering news: Forest and Bird’s representative on the Threatened Species Trust, Lyn Bates, advises rock wren will have a ‘sponsor’ this year. Chemical technology company B. Dent Global has pledged $35,000 towards capturing and moving a population of 15-25 birds to the safety of the alpine zone on Anchor Island in Fiordland. The funds will also aid assembly of basic information about the plight of the bird and what to do about it.