Rat Removal Helps ‘Primeval’ New Zealand Island

For threatened species in New Zealand, one of the country’s offshore islands and the country’s oldest nature reserve has just become safer.

New Zealand’s conservation agency, the Department of Conservation (DOC), have just finished a project to eradicate rats from Little Barrier Island, a 3,000-hectare island situated 80 kilometers east of the country’s most populous city, Auckland. About 55 tons of rat bait was spread over the island in two separate operations in the second largest island rat eradication undertaken by DOC.

“It’s hugely satisfying to have the operation finished in just six weeks after more than six years of planning,” Auckland Conservator Rob McCallum said in a statement.

If DOC has been successful — and the department can’t say definitively until two years hence — then birds such as the Cook’s petrel, insects such as the giant weta, and lizards such as Duvaucel’s gecko could once again thrive on Little Barrier Island.

“We can now look forward in two years’ time to being able to confirm the pest-free status of one of New Zealand’s premiere island nature reserves,” said Mr. McCallum.

Little Barrier is, DOC says, one of the last remnants of ‘primeval New Zealand’; it is the only large forested area left in the country relatively undisturbed by browsing mammals. As such, it is an invaluable refuge for rare and endangered plants, birds and animals whose mainland habitats have been destroyed. A campaign to eradicate feral cats was successfully completed in 1980.

Protected in 1895, Little Barrier was New Zealand’s first nature reserve and once had the largest range of native birds, reptiles and land snails of any island in the country, according to DOC. Even now, native birds thrive on Little Barrier, which has the greatest number of endangered bird species anywhere in New Zealand. The island is a sanctuary for the saddleback, stitchbird, kaka, kakariki, kiwi, black petrel, brown teal, and kokako, birds which are now extinct, or in danger of extinction, on the mainland.

Thousands of Cook’s petrel chicks are expected to survive on the island without the rats, known as kiore, to ravage the nests. In previous years up to 95 percent of chicks have been predated by the kiore leaving the petrel population in a downward spiral.

If Codfish Island — better known as the kakapo stronghold — is anything to go by, the survival of Cook’s petrel chicks will increase dramatically. After kiore were removed from Codfish, the Cook’s petrel chick survival rate leapt from 15 to 85 percent in the first year.

With kiore gone from Little Barrier other seabirds such as diving petrel, fluttering shearwater and grey-faced petrel are also likely to return, DOC hopes.

The future of threatened species such as giant weta, Duvaucel’s gecko and tuatara should also be more certain. Tuatara, which are now kept fenced for their own safety, would be released as soon as the island is confirmed as rat free.

The island is also home to more than 350 native species of plants, including 18 nationally and regionally threatened plant species occur on the island. All these, says DOC, should benefit from the removal of the rats.

In the last three years DOC has removed rodents on islands as diverse as sub-Antarctic Campbell Island, the largest to date, and sub-tropical Raoul Island in the Kermadecs. The $700,000 pest eradication project of Little Barrier Island is largely funded under the New Zealand Biodiversity Strategy.

Leave a Comment