Mice-eradication programme about to begin on the subantarctic Antipodes Island
Few people have ever ventured as far as Antipodes Island, but on one of those rare visits mice tagged along. This winter, the Department of Conservation plans to get rid of them, SARAH-JANE O'CONNOR reports.
It's a quirk of fate that mice are the only introduced mammals on Antipodes Island. The remote subantarctic island, about 750 kilometres southeast of New Zealand, was off the beaten track for most sailors who ventured into the Southern Ocean in pursuit of seals and other luxuries.
Those sealers that did arrive at the Antipodes, "made pretty short work of the seals there," according to Department of Conservation (DOC) island eradication advisory group chairman Keith Broome.
"So once they were gone, there wasn't a reason to go back to the Antipodes after that for quite a long time."
Remoteness has thrown up an array of issues for the team planning to eradicate mice from the island this winter. When Campbell Island was rid of rats in 2001, the bait-application helicopters were flown down as the pilots could island-hop if necessary. But with Antipodes Island, "there's nowhere to stop in between," Broome said.
That means everything is reliant on ships - not an easy task with furious seas, weather and an island lacking safe harbours for anchorage.
Already the eradication operation has been delayed once and earlier this year a preparatory trip was cancelled when the HMNZS Canterbury was deployed to Fiji to provide aid after Cyclone Winston.
But the eradication will go ahead this winter, with the operation team heading to Antipodes Island earlier than planned to give them time to do the work that would have been done on the Navy voyage.
They will be based on the island for several months, using helicopters to spread rodent poison, in an operation made possible through public donations.
The "Million Dollar Mouse" campaign, spearheaded by economist philanthropist Gareth Morgan, elicited $250,000 in public donations, supplemented by another $100,000 by the World Wildlife Fund. The Morgan Foundation matched the donations and DOC met the shortfall to reach the $1 million goal.
With few scientists able to visit the Antipodes, it is not clear the extent of damage mice could be having on the island. But studies elsewhere have raised red flags.
Two islands in the South Atlantic - Gough and Marion - have mice as the only introduced rodent and in both cases the mice have taken to a curious food source: seabird chicks.
Researchers filming the nests of tristan albatross in 2004 found mice attacking the chicks. In the 2013/2014 breeding season, less than 10 per cent of tristan albatross chicks - an endangered species found only on Gough Island - survived to fledge from the nest.
University of Auckland conservation biologist James Russell said an Antipodes Island expedition in the summer of 2010/2011 did not find evidence of mice attacking seabirds, "but of course that doesn't mean that it might not happen sometime in the future".
"We know that mice tend to have a bit of a shopping list when they're on islands. They go through moths and worms really quickly…then they go through beetles as well.
"So they think what happened on Marion and Gough is they've gone through all the tasty things and they're starting to get really desperate and that's why the switched on to birds - they'd exhausted the tasty stuff."
There is good reason to suspect the Antipodes mice have been chomping their way through the native invertebrates. A "mystery weta" was only spotted once on nearby, mouse-free Bollons Island, although Russell said an analysis of mouse-gut contents on Antipodes Island discovered something that looked tantalising like weta parts.
Russell recorded 150 mice per hectare on the 2000ha island, so there are suspicions that birds like pipits, storm petrels and two species of parakeet that live nowhere else might be affected by the dense mouse population.
Te Papa vertebrate curator Colin Miskelly studied snipe breeding habits for his PhD, but only visited Antipodes Island - with its endemic sub-species of snipe - once in 1990. That was long enough to notice something odd happening there.
On Snares Island, snipe start breeding in November and lay eggs over summer. But on Antipodes Island, Miskelly found large chicks in October that must have come from eggs laid in August - three months earlier than on the Snares.
Later he supplemented his observations with data from Kath Walker and Graeme Elliott, DOC scientists who visit Antipodes Island every summer to study the antipodean wandering albatross.
"It showed the Antipodes birds were doing something really strange," Miskelly said. "They were breeding really early, so from August through to about October, and then stopping through the peak of summer which is exactly the time that snipe on the Snares and Auckland Islands are breeding.
"It is very unusual. I can't think of any other New Zealand bird that has that kind of pattern of breeding, and of course the question is why."
Perhaps mice are competing with food, or an important food source for snipe breeding has been wiped out? Time's run out to find out for sure: instead the eradication will go ahead on the assumption that removing mice will be good all-round for snipe and the other Antipodean residents.