A New Chance tor Nature

Forest and Bird, Issue 312, 1 May 2004, Page 34

A New Chance tor Nature

KATHY OMBLER

tells how developina

technology is removing rats from larger island sanctuaries.

: hen pest-control teams turn later this year on the rugged ' wildlife sanctuary of Little Barrier Island, nature will get a second chance. When cats were removed from there years ago, rare bird numbers grew, sufficient to allow their capture and spread to other island sanctuaries. But while Pacific rats, or kiore, were allowed to survive on the island, its few tuatara had to be caged and their young confined to what looks remarkably like a chicken run. Experts predicted the early demise of the giant weta, and groundnesting seabird colonies remained threatened, unless the rats could be exterminated — and they can. Evolving methods for the control of rats now makes the task of removing them from an untracked, rugged mountainside technically possible. The success of these methods has been rapid and spectacular. Five years ago, conservationists celebrated the eradication of rats from the nature reserve of Kapiti Island, off the Wellington west coast. (See Forest & Bird, November 1999 for technical detail.) At the time this was by far the largest island to be rid of rats in New Zealand, but larger islands have

since been tackled, most notably the remote Campbell Islands group in the subantarctic. The Kapiti success brought to 54 the number of offshore islands, ever-increasing in size and complexity, that the Department of Conservation had cleared. The removal of rats paved the way for often-spectacular forest recovery and the relocation of threatened species to the new predator-free sanctuaries. The technology and expertise that blitzed rats from all of Kapiti’s steep and rugged 1965 hectares attracted attention from conservationists worldwide, and set the way for even more ambitious eradication targets. Bigger islands, including islands with multiple pest species such as rats and cats, and islands so far from mainland New Zealand they are at the very limits of helicopter reach, moved into the firing line. Five years on, rats and cats have been blitzed from Tuhua (Mayor Island) in the Bay of Plenty. In the remote Subantarctic World Heritage Area, Campbell Island, over 10 times the size of Kapiti and five hours’ helicopter flying from the mainland, has been declared rat free. Raoul Island, halfway to Tonga in the Kermadec group of islands, is in the final monitoring stages following a rat and cat control operation in 2002. Now in the Hauraki Gulf, after protracted negotiations, resource consent and iwi blessing have been given to the eradication of kiore from Little Barrier Island/Hauturu. Aerial pest-control operations happen in a very short space of time. However, the logistical planning, resources and technological expertise required for their successful execution are huge. Postoperation monitoring, over rough terrain in harsh environments, adds to the mammoth task. Here’s how DoC tackled the different projects. Tuhua (Mayor Island), Bay of Plenty Two significant factors marked this operation, in September 2000. First, multiple species of predators — Norway rats, kiore and cats — were targeted. Second, the operation was carried out in collaboration with the island’s iwi, Te Whanau A Tauwhao ki Tuhua. Tuhua also served as a trial for Raoul Island, which is topographically similar and contained cats, Norway rats and kiore. The key question, whether the cats would succumb to secondary poisoning from eating the dead or dying rats, was happily answered. Prior to the aerial drop six cats were fitted with transmitters. Within ten days of the operation all six cats had died, and intensive monitoring of the island since

has found no trace of either cats or rats. Predation by pests had decimated bird populations on Tuhua and the operation’s success paved the way for species relocation. In May 2003, 42 North Island robins were released on the island and within six months were successfully breeding. DoC plans the release of further species, and expects recovery of the island’s seabird colonies. Campbell Island According to the Director-General of Conservation, Hugh Logan, rat eradication has never been done at such an inhospitable site as the 11,300-hectare Campbell Island — it’s 700 kilometres and five hours’ flying time from the mainland. In the winter of 2001, two helicopters shifted 120 tonnes of baits onto the island from a ship moored offshore and another three flew bait-

spreading missions, during gaps in storms and heavy cloud cover, over a month-long period. In a survey last May, DoC scientists found no trace of rats on the island. What they did discover was significant wildlife recovery. Greg Lind, DoC’s area manager for the subantarctic islands, explains: ‘The insect life now is just incredible. Before you hardly saw any movement in the vegetation and now the place is alive with weta and other insects. There is a proliferation of perching birds, such as waxeyes, which indicate their nests are safe and there is an increase in their food. The territory of the Campbell Island pipit has increased from less than ten percent prior to the operation to over half of the island and there is evidence the island’s remnant seabird populations, such as titi and grey petrel, are increasing.

‘The next move is to accelerate these changes. We are proposing to reintroduce Campbell Island teal from Codfish Island and Mt Bruce over the next two years, although this will require huge funding and we are currently looking for sponsorship, Raoul Island With its multiple predator species and the huge distance involved, Raoul has been possibly the greatest challenge of all for the DoC eradication teams. The island lies 1000 kilometres north from the New Zealand mainland, beyond the range of most helicopters. The 52 tonnes of bait required was beyond the carrying ability of ships normally used for transport to the island — yes, even the Navy frigates. Two Iroquois helicopters loaded with nothing but long-range fuel tanks flew to the island. Meanwhile a barge carried bait, plus 30 tonnes of helicopter fuel and four gigantic spreader-buckets to Raoul. Landing these supplies in 30-knot winds was a ‘nightmare scenario, according to DoC’s project coordinator Mike Ambrose. However, the two poison drops — a main application then a follow-up five days later — went smoothly. Mike Ambrose says subsequent monitoring has shown no sign of rats; however cats have proven more problematical. ‘There was probably a 90 percent cat kill achieved through the rat poisoning, but not the 100 percent achieved on Tuhua, A programme of bait laying, trapping and searching by specialist tracker dogs has since snared four cats. "We can be fairly sure there has been no breeding of cats on Raoul since the eradication. Either there

are no cats left or there is perhaps a tom. So it’s getting close but we’re not certain yet. In the meantime, the vegetation, which had already recovered ‘amazingly well’ since goats were culled from Raoul in the 1980s, was looking even better, according to Mike Ambrose. ‘There are literally carpets of seedlings up there. Nikau is the most noticeable. As well, the Kermadec kakariki, previously extinct on Raoul, has self-relocated from the neighbouring Meyer group and is already breeding, while active petrel burrows have been seen for the first time in decades.

What's next? Eradication of kiore, the last remaining predator from Little Barrier Island, was initially planned two years ago. Now, following a long and expensive but successful resource consent process, DoC’s Auckland regional conservator, Rob McCallum, says the poison operation is now programmed for this winter. He says that after initial dissension, local iwi also supported the eradication plan. ‘There were a range of views within the Ngatiwai hapu. They are now unified in giving their support to the Department. Their concern for other taonga [treasured] species on Little Barrier, such as tuatara, dactylanthus, Cook’s petrel and giant weta outweigh their concerns for kiore. ‘DoC is going to be working with iwi, Rob McCallum says. "We are looking forward now to where we’re going with species that need rehabilitation, in particular to the most spectacular tuatara release ever done.’ At present some 90 tuatara live in cages on the island, unable to be released because their young would be at risk from kiore predation. In the meantime, ongoing efforts are being undertaken to prevent or deal with reinvasion of rat-free islands which could occur by means such as illegal boat landings or shipwrecks. The development of longlife baits, lures and bait stations attractive to rats is the focus of current studies by Landcare Research. The development of early detection systems, such as traps with remote sensing devices, have been discussed in theory at least. In Auckland, a PhD student James Russell is studying rodent behaviour patterns in controlled releases on three small and heavily modified islands,

with a view to determining optimum management methods in the event of reinvasion. While each DoC conservancy operates its own reinvasion contingency plan, the department is nearing completion of a national island biosecurity ‘standard operating procedure’, which covers measures to prevent the accidental introduction of weeds and animal predators to its offshore island reserves. — KATHY OMBLER is a Wellington-based writer.

| Problems with Poison

While brodifacoum continues to be the favoured poison for use on island aerial pest-control operations, the Department of Conservation has restricted its use of the poison for pest control on the mainland. The restriction came as a result of a review four years ago, after MAF tests had shown the presence of brodifacoum in wild pigs in game-packing houses. A DoC fact sheet states that ‘as a second-generation anticoagulant, brodifacoum is persistent in living animals for at least nine months, which means small doses can build up over time. ‘Although the real risk is difficult to measure, DoC is concerned about the possible impacts this could have on native species exposed to brodifacoum, and on people who eat game such as pigs or deer. It has chosen to take a precautionary approach.’ Keith Broome, a senior technical officer for DoC, says using brodifacoum in oneoff applications such as island operations does not constitute the same risk. Nevertheless, resource consents are sought for all offshore-island operations through the appropriate regional council. In the case of remote islands such as Campbell and Raoul, which fall under the Minister of Conservation’s jurisdiction, the Minister has sought consents from an independent commissioner. As part of the Department’s review on the overall use of pesticides, all DoC offices now have pesticide summaries that list all DoC pest-control operations happening on public conservation land. As a point of interest, major changes are likely for all agencies involved in pest control in New Zealand as the Environmental Risk Management Authority takes responsibility, during a gradual transition period, of the use of pesticides according to the Hazardous Substances and New Organisms (HSNO) Act 1996.