KEY POINTS:
Conservationists are on a mission to eliminate the last mice from a protected Waikato forest in what could be a world first in mainland pest eradication.
The Maungatautari Ecological Island Trust has been working to remove predators and pests at Maungatautari, a forested volcanic cone rising above the Waikato basin just south of Cambridge.
The 3400ha ecological reserve is surrounded by a 47km predator-proof fence and the trust chief executive, Jim Mylchreest, said a series of aerial poison drops had killed off pests such as rats, possums, hedgehogs, stoats, ferrets, feral cats and pigs within the enclosure.
Deer and goats were hunted.
"There are just a few goats left, which will be picked off, and a few rabbits and hares."
In all, 15 species of nuisance animals have been eradicated.
Now the trust wants to get rid of every last mouse in the fenced-off bush.
Mr Mylchreest said that with extensive ground monitoring and poison bait laying in the past couple of months, the recorded mouse activity had shrunk back to the northwestern boundary.
He was not sure from the data how many mice might remain as one mouse could be visiting a number of sites.
Mr Mylchreest said it would be an international first to get rid of an entire mouse population within a tall forest environment, although populations had been eradicated on offshore islands.
"It is feasible and the trust is committed to total eradication."
Mr Mylchreest said mice could present a problem as they competed for food sources such as seeds and insects.
There was also a risk they could reach plague proportions within the reserve because their natural predators had been eradicated.
Mr Mylchreest said volunteers ran a very effective monitoring exercise.
There were 170km of monitoring lines in the forest and it was planned to increase that to 230km so no single spot would be more than 200m from a monitoring tunnel.
The monitoring had started out weekly but as confidence increased that the pests were staying out, it was now three monthly.
The goal was to restore the forest to a healthy diversity of endangered flora and fauna not seen there in a lifetime, such as tuatara, kakariki, saddleback and stitchbirds. Populations of kiwi, takahe and kaka had already been restored within the enclosure.
Mr Mylchreest said the predator fence was proving robust.
Landcare Research scientist John Innes last year released six male rats carrying radio transmitters back into the enclosure to see how they behaved.
Interestingly, given the abundant food sources within the sanctuary, most jumped out of the enclosure within days (the fence is designed only to stop pests getting in).
"It is possible they were looking for company or wanted to mate."
Mr Innes said all the rats had at one point climbed on top of the fence, which was useful information for positioning bait should any rats climb into the reserve via a fallen tree.
