Jo Ledington, Zealandia's general manager of conservation and restoration. Photo: RNZ / Kate Green
Wellington's most famous fence is nearing the end of its lifespan, with a design for its replacement under way 25 years after it was first installed around Zealandia.
It was the first of its kind worldwide when it was built in 2000, and now, the eco-sanctuary is home to some rare and protected flora and fauna, including parasitic plants, kiwi, takahē and tuatara.
That initial fence design process in the early nineties involved a prototype built in a Wellington warehouse, a handful of rodent-y test subjects and some video cameras to capture their attempts to scale it.
What emerged was the fence we know today, between 2.1 and 2.4 metres high, made of tight, mouse-proof wire mesh which extends a little way underground, and with a rounded cap on top, to keep pests from climbing over.
But by now, Jo Ledington, the sanctuary's general manager for conservation and restoration, said it was beginning to reach the point where the cost of maintenance outweighed putting in a replacement.
And that meant opportunities for improvement - starting at the front gate.
"You hear that clanging?" Ledington said, letting it swing shut with a bang. "It's like going through prison gates, so I would like to see that just be a bit more welcoming."
The entranceway could be in for a redesign when the rest of Zealandia's fence is replaced. Photo: RNZ / Kate Green
On the fence itself, the metal seams along the cap on top were rusting, some posts were leaning, and Ledington said they could do with wider emergency exits for better vehicle access.
There would also be some tweaks to accommodate some of the sanctuary's newer residents - tuatara.
"Tuatara dig, they burrow," Ledington said. "Sometimes we've had burrows that look like they could come all the way out.
"So we have an external skirt that is dug into the ground about 30 centimetres, and then comes out about 30 centimetres, and that stops rabbits from digging down under, so we're keen to look at doing something similar on the inside."
It could be that sections were fully replaced, and others only altered.
A tuatara at Zealandia Ecosanctuary. Photo: Ellen Rykers
Right now, Zealandia was seeking donations to help pay for it - although just how much it would need was not yet known.
But Ledington could offer a guess. "If we looked at the cost of the original fence, and then applied inflation to that, we'd be looking at about four to five million."
One thing they did know -- they weren't planning to do this again, hopeful that by the time this fence reached the end of its life, the country would have reached its predator-free goal, meaning no need for a fence at all.
Detailed designs were expected in September, which would shed light on the materials and the cost.
Jo Ledington points out her favourite part of the original Zealandia fence design which stops mice looping their tails around the bolts to get up and over. Photo: RNZ / Kate Green
Standing just outside the sanctuary's entrance, Ledington pointed out her favourite part of the original fence; a piece of flat metal measuring about five centimetres, sheilding long bolts on the interior of the curved cap.
"That was a last minute addition, because what they found was that mice were crawling up here, and putting their tail around this bar here, and using their tail to flick themselves up over the hood."
The only thing causing concern for Ledington was the risk to the sanctuary's inhabitants of deconstructing their protective barrier, no matter how temporary. "We now have this huge duty of care to everything we've put in here," she said.
Working on the new fence's design was engineering consultancy firm GHD, who were doing it for free as part of their global pro-bono work programme.
Technical director Justine Jones headed up a team of seven, and said so far it had been an engaging challenge compared to their normal work of buildings and pipes.
"The team are nearly all Wellington based, they go to Zealandia, they're invested in the project," she said.
The original build had required some unusual techniques.
"They did a lot of research," she said. "As I understand it, they built a prototype, and then in a warehouse they put the fence up, put something tasty on the inside of the fence, and then released rats and stoats and things and then recorded them to see how they got to the food."
The fenceline is dotted with signs asking people not to inadvertently create a bridge for leaping predators. Photo: RNZ / Kate Green
Since then, the blueprint had been used for dozens of other predator-proof fences around the world.
"What we've been doing is speaking to some of those other sanctuaries who have installed fences more recently, and understood the changes that they have made in their design, and speaking to the suppliers that we have to see what might be available that wasn't before," Jones said.
It was a big job, on steep terrain, and it had to be done right - neighbours notified, and the integrity of the fence maintained while work was carried out.
That meant machinery could not be left close to the fenceline after work hours, as pests could use it to climb over, and any gear or machines taken in would have to be decontaminated and quarantined.
Zealandia's chief executive Danielle Shanahan said the first 100-metre section would be replaced by the middle of 2026, and then over the next five years they would begin picking up pace.
Dr Danielle Shanahan, CEO of Zealandia. Photo: Zealandia
Some of the funding garnered already was coming from the estate of John Nankervis, a Wellington tramper and mountaineer who left millions to conservation efforts on his death in 2022.
Shanahan said this early work was important for creating a reliable blueprint for the replacement of the fence as a whole.
"Because we've got many species inside that are vulnerable, we need to do this with great care, we can't just rip the whole thing down and stick a new one up," Shanahan said. "We'll do it piecemeal, and in sections."
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