Last shot fired against rats on Little Barrier

Little Barrier Island, 90km northwest of Auckland, should soon be free of rats.

Rob McCallum, Auckland conservator for the Department of Conservation, said the second aerial drop of rat bait on the 2817ha island this week was a significant step in its development into a premier nature reserve.

The drop was successfully completed on Monday in perfect conditions, after an initial drop in June.

"It's hugely satisfying to have the operation finished in just six weeks, after more than six years of planning," he said. "We can now look forward in two years to being able to confirm the pest-free status of one of New Zealand's premier island nature reserves."

The absence of rats is expected to first show up as a huge boost in the survival of cook's petrel chicks.

Thousands more of the chicks are expected to survive on the island without kiore to ravage the nests. In previous years up to 95 per cent of chicks have been eaten by the Polynesian rat, leaving the petrel population in a downward spiral.

After rats were removed from Codfish Island, near Stewart Island, in 1988, the chicks' survival rate leaped from 15 to 85 per cent in the first year.

Little Barrier is the stronghold of this native seabird, with a population of 50,000 breeding pairs, but several hundred birds also nest on Codfish Island.

Other seabirds such as diving petrel, fluttering shearwater and grey-faced petrel are likely to return to Little Barrier, and the future of threatened species such as giant weta, duvaucel's gecko and tuatara will also be more certain.

It had been estimated that there were once more than 300,000 tuatara on Little Barrier, but rats eating the reptiles' eggs and babies reduced the population to the point where they were thought to be extinct on the island.

A small number were rediscovered in the 1990s, and have since been held in captivity and their numbers lifted to more than 100 by successful breeding.

They will be released as soon as the island is confirmed to be rat free, in about two years.

Protected in 1895, Little Barrier once had the largest range of native birds, reptiles and land snails of any island in the country, and was home to the last natural population of stitchbird and giant weta.

Victoria University professor and tuatara expert Charles Daugherty has predicted that once the rats are definitely gone insect life will return quickly, and then lizards and tuatara will be able to thrive.

But Mr McCallum said the most dramatic comeback would be from cook's petrel, which were burrowing seabirds. They were thought to number more than half a million in the early days, but nobody had seen a juvenile petrel for 10 years.

Removing kiore from Little Barrier is the second largest island rat eradication undertaken by DoC after sub-Antarctic Campbell Island.

- NZPA