In August 2022, conservationists were alarmed to find evidence of a stoat on Chalky Island (Te Kākahu-o-Tamatea), a small, rugged island sanctuary in Fiordland, New Zealand, that had been predator-free since 1999. The discovery was a major shock, as stoats had been deliberately kept out for decades. The Department of Conservation (DOC) immediately launched a full-scale incursion response, treating the single stoat as an urgent threat. They deployed trained conservation dogs, expert trappers, trail cameras, and even helicopters and boats to scour the island’s 511 hectares for the elusive animal. In New Zealand, even one stoat can spell disaster for native species.

Chalky Island shelters a wealth of vulnerable and endemic wildlife, including the Te Kākahu skink (found nowhere else), the critically endangered kākāpō (a flightless nocturnal parrot), and rare birds such as the mohua (yellowhead), tīeke (saddleback), and little spotted kiwi. These species evolved without mammalian predators, leaving them defenseless against a stealthy carnivore like the stoat. Just one can raid nests, kill chicks, and even take adult birds with alarming efficiency. DOC officials warned that if the intruder wasn’t caught quickly, it could wipe out chicks and lizards on the island, undoing years of conservation work.

The stoat (Mustela erminea) is a small carnivorous mammal in the weasel family, and it is not native to New Zealand. In the late 1800s, European settlers introduced stoats, along with weasels and ferrets, in a misguided attempt to control exploding rabbit populations that were damaging farms. Scientists at the time warned that these predators would devastate New Zealand’s unique birdlife, but the warnings went unheeded. The prediction came true: stoats spread rapidly across the country, and within a few years, native bird numbers were in steep decline.