Suspicions mice are getting through the corners and culverts of Orokonui Ecosanctuary's predator-proof fence has led to plans for an upgrade.
The 9km fence was state of the art when it was built in 2007 but now needed fine-tuning to stop mice.
General manager Chris Baillie said the ecosanctuary was awaiting the results of a recent dye trial to determine the extent of the mice problem.
It was thought the corner canopies could be one weak point and the facility, with help from one of its trustees, was retrofitting the corners to prevent the problem.
"We got the best fence at the time but using it over time you identify improvements," she said.
Trustee Graeme Leith had designed a metal disk that protruded from the hood on the corners to prevent mice climbing over it, she said.
The problem had not threatened the ecosanctuary's pest-free status as mice numbers were still well under the 5% threshold, she said.
"We've just had low numbers of mice popping up in certain areas and we think that is where they're maybe coming in."
Work to prevent mice getting in through culverts was also planned.
But as it was more expensive, the ecosanctuary needed funding help to carry out the work, Ms Baillie said.
Kiwi have been seen and heard on the first Orokonui After Dark tour this week.
Orokonui head guide Sue Hensley was leading two people on the first tour at twilight when they heard calling and later came upon a kiwi on one of the ecosanctuary's walking tracks.
A second sighting occurred on a different track, Ms Baillie said.
Tracking studies based on transmitter signals showed the kiwi had a preference for the upper part of the sanctuary, around the open grassy areas, she said.
However, there was no guarantee people would continue to see the kiwi on the tours.
