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Last Updated: Thursday, 28 July 2005, 19:16 GMT 20:16 UK
NZ tackles its island pest problem
By Kim Griggs
in New Zealand

Pest fence, Kim Griggs
Huge fences are being used to keep the pests out
When the pest eradication team from New Zealand's Department of Conservation (DOC) arrived on the sub-Antarctic Campbell Island, they hunted for an iconic New Zealand insect, the weta.

"They had been reported there in the past. One guy spent a year there and saw one," explains Lindsay Wilson, a member of the DOC team.

"We went searching for them. We didn't see any."

But after poisoning the introduced Norway rat population, the weta, along with many other island fauna, rebounded.

"When we went down there on the follow-up visit, the first bush we looked under, there were half a dozen of these weta," says Wilson.

Rat poison

New Zealand has developed undoubted expertise in the business of eradicating invasive pest species from islands.

It is a major problem. The recent Millennium Ecosystem Assessment showed that invasive species were responsible for the greatest loss of biodiversity on islands; and second only to habitat loss globally as a major cause of extinctions.

A mouse eats the remains of a petrel (RSPB)

And this week, the UK announced it would be seeking New Zealand's advice on dealing with the mice that were attacking albatross colonies on one of its South Atlantic territories.

New Zealand first managed to eradicate rats from a group of small offshore islands in the early 1960s.

Now it is tacking more and bigger islands thanks to two modern technologies: second-generation anti-coagulant bait and the GPS systems that allow bait to be applied with precision from helicopters.

"Prior to that, rodent eradications were typically on small islands and they were done as ground-based," says Alan Saunders, a former long-serving DOC staffer and now University of Auckland conservation ecologist.

These days pilots follow a grid pattern to ensure an island is swathed in bait, with printouts of the paths flown enabling the conservation team to check for any gaps.

The 11,300-hectare (27,900 acre) Campbell Island, the biggest of the more than 100 islands New Zealand has cleared of pests, is one of the most challenging eradications that DOC has so far attempted.

Maungatautari, Louise Dwan
Maungatautari is being ringed with a 47-kilometre predator-proof fence (Image: Louise Dwan)
It is surrounded by 200m-high (660ft) cliffs, is battered by wind and rain almost all year round, and has an average temperature of just 6 degrees Celsius (43 degrees F).

The island also had the world's highest density of Norway rats.

But it took the team three weeks one winter - a flying hazard, the albatrosses are fewer there then - to apply all the bait and now, a few years on, the island is once again a haven for fauna such as weta, the New Zealand pipit, the Campbell Island snipe and one of the world's rarest ducks, the Campbell Island teal.

"The DOC have yet to fail in an aerial eradication operation for rodents," says Saunders.

Kiwi returns

The New Zealand conservationists have also eradicated mice from 12 offshore islands, one as large as 710 hectares (1,750 acres).

Mice don't range as far as rats so the bait needs to cover "every little nook and cranny," says Wilson.

Kiwi, Kim Griggs
Four North Island brown kiwi have been reintroduced into a small pest-free enclosure
So fine-tuned is the DOC technique that "virtual" islands are now springing up on the country's main islands.

In the middle of New Zealand's North Island, a community group is half way through ringing 3,400 hectares (8400 acres) at the top of a local mountain, Maungatautari, with a 47km (29 miles) predator-proof fence.

When the fence is completed, the mammalian pests within will be poisoned.

Already four North Island brown kiwi have been reintroduced into a small pest-free enclosure on the mountain, the first kiwi there in living memory.

Says Saunders: "The bottom line is that you just make sure that every rat has access to bait and if you do, then they'll all be dead."

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