We’re aiming high with our Predator Free 2050 ambition. It’s a big goal, and a unique one. But everything we know about eradicating pests on the mainland, we learned on islands.

This is the seventh blog in Brent’s PF2050 series.

By Brent Beaven, Programme Manager Predator Free 2050

Everything we know about eradicating pests on the mainland, we learned on islands.

In 1959, a small boatload of Forest & Bird volunteers bumped ashore on Maria/Ruapuke Island in the Hauraki Gulf and placed rat baits, the first tentative step on a journey that today sees Aotearoa as an acknowledged world leader in island pest eradications.

Ruapuke is tiny — just a couple of hectares — but it’s a landmark in conservation history as the site of the world’s first successful rat eradication.

It also inspired wildlife managers to much greater things. By applying lessons learned from smaller islands, they’ve been able to scale up their efforts and ambitions: in the 70 years since Ruapuke, pests of all kinds have been removed from more than 110 islands all around our coast, each one bigger than the last, culminating in subantarctic Motu Ihupuku/Campbell Island, at 12,000 hectares.

Rats, stoats and possums have driven many native creatures from the mainland altogether, so that pest-free islands are now the arks of Aotearoa. Without them, some species would have nowhere left to live.

They also make ideal testing grounds for new eradication methods, which makes them a key objective in the Predator Free 2050 Strategy.

On the mainland, a study site can be re-invaded by pests from surrounding countryside, making results difficult to measure. But there are no such difficulties on a remote island, giving researchers a much clearer picture of what works and what doesn’t.

To visit an island free of pests is to glimpse how Aotearoa looked and sounded before mammalian predators turned up. If you’re lucky enough to wake up at anchor off Manawatāwhi — the Three Kings Islands — hundreds of korimako/bellbirds will treat you to one of the best dawn choruses anywhere.

Take a stroll at dusk on Hauturu-o-toi/Little Barrier and you’ll see the flitting figures of pekapeka-tou-roa, or long-tailed bats, against the fading light. Wētāpunga — giant weta — will be emerging from their hiding holes, and geckos will be climbing into the canopy to feast on nectar. The place comes alive.

On Takapourewa, or Stephens Island, in Cook Strait, dusk is when hundreds of thousands of seabirds return to their burrows, just as tuatara are emerging to hunt.

Some Nature Reserves, like Kāpiti Island off the Horowhenua coast, are open to the public, and you can see native wildlife now rare or lost altogether from the mainland. On Kapiti, expect to be mobbed by kākā, see takahe leading their gawky chicks through the tussocks. The leaf litter twitches with the scurry of lizards. On Tiritiri Matangi, hear the chattering challenge of tīeke, or the gorgeous notes of the kōkako.

On a pest-free island, you realise how Aotearoa once rang with birdsong, and how the fragrance of blossom would have wafted everywhere on the air.

You can see how birds like kākāriki, kererū and kōkako once spent much of their day feeding on the ground, in complete safety. You can start to appreciate how diverse, intact ecosystems might once have worked.

In that sense, they offer us a glimpse of the future, too: of what we can expect the mainland to look and sound like once again, if we strive for a Predator Free 2050.

One of PF2050’s interim goals is to rid New Zealand’s remaining uninhabited offshore islands of mammalian predators by 2025, but there’s a hurdle in the way, called Maukahuka.

Part of the subantarctic Auckland Islands group, Maukahuka lies astride the Furious Fifties, 465 kilometres from Bluff. It stands in the path of some of the harshest weather and hugest seas Nature can muster — 46,000 hectares of desperate travel through dwarf forest, scrub and peat bogs. But as the fifth-largest island in Aotearoa, it’s biologically one of the richest in the subantarctic. The lower slopes are draped in southern rātā, stunted by the cold and the wind, but no less glorious in summer bloom.

The island’s open country should be rampant with megaherbs, but the ground is bare, ransacked by wild pigs. Released here in 1807 as sustenance for sealing gangs, pigs have had a devastating impact, eating the eggs and chicks of seabirds that would once have numbered in their tens of thousands. Between them, the mice and the cats, they’ve extirpated 32 bird species from Maukahuka, and wrecked an intricate nutrient cycle powered by seabirds.

The New Zealand subantarctics are a World Heritage site, recognised for their unique biodiversity. Maukahuka is the last of them to harbour pests, and if they were removed, it would add another 420 per cent of safe habitat for native biodiversity in the group — particularly the four species of albatross mostly confined to other pest-free islands in the group.

And while Maukahuka presents perhaps the toughest eradication challenge of all, field studies have confirmed it can be done. The pigs can be cleared using traps, aerial hunting and ground hunting with dogs. The mice will need a departure from standard practice, with aerial baits sown at half the usual rate, in summer rather than winter to exploit the short weather windows.

Cats can be dealt with by a species-specific toxic bait and ground hunting. All up, it’s expected to take ten years, and that’s why the 2025 islands target is the least likely of the PF2050 interim goals to be met.

Historically, island eradications have been ad hoc, assembling the necessary expertise, funding and equipment practically from scratch, and each successive project had to duplicate the process. It all took time and repeated investment. This year, all that changed with the establishment in DOC of a dedicated team of specialists.

The National Eradication Team (NET) will guide the clearance of our remaining islands with ecological and technical advice. Through feasibility studies, it’ll prioritise each island according to scale and its “defendability” — the likelihood of keeping predators off it once it’s been cleared. The NET brings a continuity of skills, and the co-ordination of resources to mount eradications more efficiently, with less duplication.

A predator-free Rakiura, or Stewart Island, is one of the most exciting prospects. Rakiura has always banked on its natural capital, and the gazettal of a national park there in 2002 put it on the itinerary of between 36,000 and 40,000 nature fans each year.

That’s because it holds a trump card: mustelids — weasels, stoats, ferrets — never reached there, which is one reason kiwi can wander about in broad daylight. On Ulva Island, in Paterson Inlet, people can see tīeke, mōhua, kākāriki and tītipounamu all in the space of a morning.

But the island’s forest is browsed by possums and deer, and rats and wild cats take a heavy toll on wildlife, leading in 2019 to the signing of a Memorandum of Understanding between the four Papatipu Rūnanga of Murihiku, us at DOC, Southland councils, Real Journeys and the New Zealand Deerstalkers’ Association to pursue a predator-free Rakiura. It would be the country’s biggest sanctuary, protecting highly endangered species such as kiwi, the tūtiriwhatu/New Zealand dotterel, and the tawaki, or Fiordland crested penguin. It would also allow for the return of species long since lost from the island, like kākāpo and kōkako.

In 2020, the project got a multi-year funding boost, which allowed eradication planning and design to begin.

Meanwhile, Predator Free 2050 Ltd has funded a feasibility study to inform Tū Mai Toanga, a proposed eradication project on Aotea Great Barrier Island, in the outer Hauraki Gulf, along with three staff. Tū Mai Taonga is also supported by the us at DOC, Auckland Council, sanctuaries and conservation groups.

So while the interim goal of having all eradications completed on offshore islands by 2025 may go unmet, an exciting new chapter in the story of island eradications in Aotearoa is opening: the fight against introduced predators has moved to those isles that people call home, too. That boatload of volunteers would never have dreamt, all those years ago as they set out for Ruapuke Island, that they were writing the open pages of such an inspiring tale.

To hear Brent talk about our Predator Free 2050 goal, have a listen to the DOC Sounds of Science Podcast, which is available wherever you get your podcasts.

#23 Deals with seals – DOC Sounds of Science Podcast

1. #23 Deals with seals 36:34
2. #22 Kaitiaki kauri, protecting the mighty kauri 38:19

For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit https://www.doc.govt.nz/moving-towards-pf2050