Fences II: Back from the Brink
How a world-first fence is saving New Zealand’s wildlife
We continue our series on fences with a guest post from Melanie Newfield. The New Zealand native writes about conservation, climate change, and COVID-19 on her Substack newsletter, The Turnstone.
In the tree above me is a small bird, singing a song that seems disproportionately loud for its size. I’m looking up, and occasionally I see him hopping from branch to branch, a silhouette against the sky. I stand and listen for some time, knowing that I’m hearing something special.
The bird is a North Island robin, a grey bird with the endearing habit of checking out humans that enter its territory. Robins sometimes come quite close – I’ve already had one within two yards of me. The species isn’t particularly rare, but it is much less common than it used to be, and in decline. Today, though, the robin singing above me is the third I’ve seen in the last half hour.
Here at Zealandia sanctuary, the species is thriving.
Zealandia is one of the world’s most remarkable bird sanctuaries. It is located in Wellington, New Zealand’s capital city, just a few kilometres from the centre of town. It’s not a zoo – the birds are free to fly wherever they want to, and they frequently visit the backyards of people who live near the sanctuary. Some of the rare birds released there have even established populations in nearby parks. But although the birds at Zealandia fly free, the sanctuary is surrounded by a 7.2 foot tall fence – designed not to keep animals in, but to keep them out.
If it weren’t for Zealandia’s fence, there wouldn’t be any rare birds in this area at all. Many of New Zealand’s rare birds are found only on remote offshore islands, because they’ve been wiped out on the mainland by introduced predators like rats and stoats. Others, like the robin and kiwi, are found in remote areas of forest on the mainland, where they continue to decline unless predators are controlled. In most New Zealand cities, only the hardiest native species remain.
Zealandia’s fence was the idea of local conservationist, Jim Lynch. In the early 1990s, he proposed building a fence around an area of forest that had formerly been a water supply catchment. But any old fence wouldn’t do the job – to keep out species like rats, cats and stoats, it needed to be a completely new type of fence. It needed to be high, it needed to go below the ground to prevent digging, and it needed to prevent agile animals like rats from climbing over it.
Coming up with the final design for the fence took several years of testing, using five different introduced mammals: cats, Norway rats, Australian brushtailed possums, stoats and mice. In 1998, the testing was completed, in 1999 the 5.3 mile fence was built and the following year all mammals inside the fence were eradicated.
The robin gives a great illustration of the impact Zealandia’s fence has had on rare species. Unless they are safe on a predator-free island, robins are sparsely distributed, occupying territories of 2-12 acres and there are almost twice as many males as females. Predators often kill female birds when incubating their eggs. In Zealandia though, the robins reach much higher densities, and have similar numbers of males and females.
The success of the robins at Zealandia isn’t obvious just to scientists. Visitors to the sanctuary are likely to meet them, because robins are fearless around humans. Seeing and hearing rare birds thriving in a predator-free sanctuary gives a powerful message about what New Zealand lost when rats, cats, possums and mustelids were introduced to New Zealand. Equally powerful is the message about what can be gained. For some of New Zealand’s birds it is too late, but Zealandia shows that native birds can be brought back from the brink, and not just on offshore islands, but in the middle of a city.
Outside Zealandia’s fence, rare birds risk being gobbled up by predators as soon as they land. That’s where Wellington’s local government and dozens of dedicated volunteers come in. Inspired by Zealandia’s success, they have an ambitious programme of predator control across the city, protecting the rare birds that have spread beyond the sanctuary boundaries. Volunteers check a network of traps, while expert pest controllers are employed to lay poison in bait stations designed to keep people, pets and birds safe. The programme has been so successful that some of the birds released in Zealandia are now breeding outside the sanctuary.
One of the most obvious success stories from the predator control has been New Zealand’s bush parrot, the kākā. Twenty years ago, most New Zealanders would never have seen one, since they were confined to offshore islands and large, remote areas of forest. Now, this cheerful clown of a bird is frequently seen in gardens around Wellington. They can also be found, once again, on the hill that bears their name, Tarikākā. For 100 years, there were no kākā in Wellington, and the name of the hill was simply another reminder of what had been lost. Now, thanks to Zealandia and its fence, there are kākā once again on Tarikākā, and the hill has regained its identity.