Rodent plague threatens kiwi

By KINGSLEY FIELD

Conservationists have launched an emergency rescue of kiwi chicks after a population explosion of rats, mice and stoats.

Wildlife experts say that pest numbers are reaching plague proportions with their highest numbers for 10 years.

They fear the vast numbers of rodents and mustelids will lead to a big kill this winter of native birds, insects and invertebrates.

The problem stretches from the beech forests of the central North Island and from Nelson Lakes to Southland where trampers have reported vast numbers of rats and mice scuttling through the bush.

Dr John McLennan, a Hawkes Bay scientist heading a kiwi recovery programme around Lake Waikaremoana, says stoat catches have been the highest since the programme began six years ago.

"We are getting up to 15 stoats a day in our traps. Normally we rarely see them in the bush but now we are seeing them almost every day. You can hear rats scuffling in the trees at night - the rodents are in there in their millions."

Dr McLennan said seven out of nine kiwi in early-season hatchings had been killed by stoats.

The rescue team was now taking the second clutches out of the bush to rear them in captivity before releasing them into the wild.

The rodent problem has been blamed on excessively heavy beech mast or seeding through the spring of 1998 which coincided with fruitings of other native trees including hinau, miro and most podocarp species providing food for rodents.

This, coupled with the dry weather last winter, meant that the survival rate was much higher than normal with rodents breeding in larger numbers this year.

The only area where their numbers have not boomed is on the West Coast where there have been no beech mast seasons in the past few years.

Stoats, which regulate their litter numbers to the availability of food, have been of particular concern to conservationists. They fear the mustelids will switch their attention to native birds and other vulnerable species as rats and mice die as a result of dwindling food supplies.

In Southland, Department of Conservation officer Andy Cox said: "We run a stoat trapping line throughout most of the Eglington Valley. Our catch rate has gone through the roof."

Species such as the native yellowhead, blue duck and brown teal are likely to be targeted by stoats once rodents disappear. In Fiordland the yellowhead is declining and the brown teal are on their last legs.

In forests around Auckland, including the Hunuas and Waitakeres, rodents have reached record levels as in the central North Island, the Nelson-Marlborough region and Trounson Kauri Park near Dargaville.

Experts say little could have been done to halt the rodent and mustelid boom. It would be impossible to spread enough rodenticide throughout the bush and not enough was yet known about mustelids to trap them in big numbers.

Last night, Dr Hugh Robertson of DoC's kiwi recovery programme said stoats would attack and kill kiwi they encountered irrespective of whether there were plenty of mice and rats for them to feed on.

"We have been running Operation Nestegg in other parts of the country such as Northland and the Tongariro Forest and the West Coast of the South Island to try and boost kiwi numbers, irrespective of the beech factor.

"But if the technique is proven to be effective, we may step up the operation in beech mast years as well."