Plague of mice on subantarctic Antipodes Island may be living on borrowed time
The Department of Conservation is aiming to remove mice from Antipodes Island this winter. SARAH-JANE O'CONNOR looks back at the eradication that paved the way 15 years ago.
The rats probably arrived on Campbell Island in 1828, when the sealing brig Perseverance was shipwrecked that October.
By 1840, when the first naturalists arrived on the far-flung subantarctic island, the damage had already been done. Those aboard James Clark Ross's Erebus and Terror expedition had just been to the Auckland Islands and noticed Campbell was missing many of the land birds of the Aucklands.
They were right: there was a parakeet already extinct; a flightless duck banished to tiny islands offshore; a snipe similarly banished, not to be "discovered" by scientists until 1997.
In 2001, the Department of Conservation (DOC) tackled a job many thought was impossible: they rid Campbell Island of the norway rats that had pillaged the island for more than 150 years.
Pete McClelland was the project manager for the operation, which at the time was the biggest island eradication ever attempted.
"It was whole new ground," McClelland said. "The largest eradication before had been Kapiti [Island] at about 2500 hectares and then suddenly we were drumming it up to 11,000 ha and also instead of operating 10km off the coast we were 700km off the coast."
Until that point, island eradications using brodifacoum - an anticoagulant poison commonly sold in stores as Pestoff or Talon - used helicopters to make two bait drops, one of 8kg per hectare and the other of 4kg per ha. But the size of Campbell Island and the likely weather conditions in the region known as the Furious Fifties meant it could have taken six months to manage two bait applications.
So methods were tweaked and in the winter of 2001, after a successful test run, helicopters were flown down to distribute a single bait drop, at 6kg per ha Five years later, when monitoring had found no trace of rats, the eradication was declared a success.
Fifteen years on from the operation, some of the benefits from rat removal are confounded by sheep being taken off the island, starting in 1970 (they were a remnant of a failed attempt at farming). But McClelland said the regrowth in vegetation was remarkable compared to when he first visited Campbell Island in the late 1980s.
More directly, weta numbers increased, pipits and snipe recolonised from smaller rat-free islands nearby, grey-backed storm petrels and white-chinned petrels were recorded breeding for the first time after the rats were gone. By 2004, DOC was confident enough to reintroduce the Campbell Island teal, a flightless duck that had been taken from a nearby rat-free island and bred in captivity until the eradication had been completed.
DOC island eradication advisory group chairman Keith Broome said, for a species like the teal, the eradication "sort of turned back the clock for them to the time before rats arrived on the island".
"More or less they've come off the endangered species list as a consequence and, apart from making sure predators don't get back on Campbell, there's no further kind of action required, there's no further conservation spending on it."
It was while teams were searching for more teal that they accidentally stumbled across the Campbell Island snipe on nearby Jacquemart Island. Though the 20ha island is only 1km away from Campbell Island, its steep cliffs mean hardly anyone has visited and then only briefly by helicopter.
Te Papa vertebrate curator Colin Miskelly helped describe and name the new snipe subspecies, which recolonised Campbell Island after the eradication without human intervention.
Miskelly said little was known about keeping snipe in captivity and there were likely too few birds to move from Jacquemart Island.
"We were fretting that if we caught some to move them, you're potentially wiping out the only natural population in the process and taking a gamble on whether they'd survive and breed where you're going to let them go. So it was a great relief when they did it themselves."
McClelland said clearing Campbell Island of rats had a huge impact on other international eradication efforts.
"That opened up a whole new spectrum of other islands that could be considered and could be done. The Australians would never have done Macquarie [Island] if it hadn't been for Campbell, the Brits would never have tried South Georgia, the Yanks would not have done the Aleutians, they were all considered too hard to do until Campbell was successful.
"It started a new wave of eradications."
With DOC preparing for an operation on Antipodes Island this winter in the hope of eradicating mice, McClelland said some people still struggled to believe an island could be freed of introduced mammals.
"The public still doesn't believe that you can get every rat off an island. Around your house you've always got mice coming in or rats coming in and you never get on top of them.
"There's something in the psyche that a lot of people just cannot understand how you can eradicate. They just don't believe that you can get something as small as rats, let alone mice, off an area of that size.
"So it's always great to prove them wrong."