Wiping out invasive pests on islands has been hailed as a crucial approach to conservation in a new global study that highlights New Zealand as a prime example.
The study, which involved 30 international scientists and was published this week in major journal Proceedings of the National Academy of Sciences, provides the first global examination of measuring the benefits of eradicating invasive mammals on islands.
New Zealand, which adopted the strategy of pest-free island sanctuaries decades ago, was singled out for how it had brought critically endangered species back from the brink of extinction.
"New Zealand is a world leader in island eradication, and this study also shows that we are leading the world in saving species from extinction using this conservation tool," University of Auckland ecologist Dr James Russell said.
"Half the species populations found to have benefited from mammal eradications come from New Zealand."
In 1964, when the late Don Merton and fellow conservationists declared Maria Island in the Hauraki Gulf free of troublesome Norway rats, the area of our islands clear of mammalian predators stood at about 0.5%.
Today, the rate is about 10%.
More than 90% of our smaller, natural reserve islands have been cleared, most recently Campbell Island and Secretary and Resolution Islands.
These offshore strongholds provide safety for a diverse range of native species, including the kakapo, takahe, tuatara, hihi, black robin, tuatara, two key species of weta and New Zealand's largest living lizard, the Duvaucel's gecko.
It is estimated that $31 billion is spent globally each year on conservation, of which a tiny fraction goes to island pest eradication.
Looking at the overall costs and benefits, island eradication more than holds its own, said the study's lead author, Dr Holly Jones, of Northern Illinois University.
Island eradication of invasive mammals has brought four species around the world to a lower threat level on the International Union of Conservation for Nature's "Red List" of species.
The list ranks the most critically threatened species around the world.
Examples of successful eradication programmes in New Zealand include the New Zealand storm petrel, thought to be extinct for more than 150 years but recently found breeding on Little Barrier Island in the Hauraki Gulf after an intensive cat and rat eradication programme.
Dr Russell said people tended to think of pest eradication programmes as being on remote islands, well away from human populations, but the latest thinking considers mammal eradication on islands where humans also live.
"Saving New Zealand's rarest species from extinction by eradicating introduced mammals is fantastic, but we shouldn't restrict this type of conservation to uninhabited islands where the species are locked away from the public.
"It would be great if people could live on the very same islands as our most threatened species."
Professor Bruce Clarkson, of Waikato University's Environmental Research Institute, said island sanctuaries were one "silver bullet" for biodiversity conservation, but other measures were still needed.
"Offshore islands can never save all of New Zealand's indigenous biodiversity as they are unrepresentative of the full range of ecosystems and habitats of the New Zealand archipelago.
"Offshore island restoration is also significant as the springboard for the later development of mainland island approaches and the new frontier urban restoration, which seeks to reconnect New Zealanders with their biological heritage by reinstating key species in urban environments, for example [Wellington sanctuary] Zealandia."
Environmental Defence Society senior policy analyst Dr Marie Brown said all of New Zealand's landmass was an "island" by definition, so the paper illustrated the game-changing effect that a transformative project like Predator Free New Zealand could have.
"We'd be having very different conversations about conservation in the absence of pests," she said.
"The challenge here and elsewhere is to work out how to best apply those techniques to populated areas."
