Stewart Island Dotterel Posts Biggest Population Gain in Thirty Years After Aerial Predator Drop

The Southern New Zealand dotterel — known by its Māori name pukunui — has posted its biggest population increase in more than three decades, following an aerial 1080 operation across half of its only known breeding ground on Stewart Island last year. The result has lifted hopes that one of New Zealand’s most precarious shorebirds may finally be pulling back from the edge.

Numbers recorded after the August 2025 operation show the pukunui population rose from 105 birds to 160 — a gain of 52 percent. It is the largest single increase recorded since active recovery efforts for the species began 32 years ago, and it gives conservationists reason to believe the long-term target of 300 birds by 2035 is within reach for the first time.

The pukunui breeds only on Rakiura Stewart Island, nesting on exposed mountain tops before coming to the coast. That narrow range and specialised habitat have always made the species vulnerable, but the most immediate threat has consistently been feral cats. Before last year’s intervention, cats were killing between 40 and 50 adult birds every year — a rate that, for a species numbering barely a hundred individuals, was simply unsustainable.

Earlier attempts at predator control through year-round trapping produced limited results. The island’s large rat population would find and eat the trap baits before cats ever encountered them, creating a frustrating ecological feedback loop. Trapping was treating a symptom while the underlying predator pressure on nesting adults remained largely unchanged.

The 2025 operation, run jointly by the Department of Conservation and the non-profit organisation Zero Invasive Predators, used a different approach across 40,000 hectares of the island — covering roughly half the known pukunui breeding areas and surrounding forest. Cereal baits laced with 1080 were dropped aerially ahead of the breeding season. Rats consumed the baits directly. Feral cats, which then preyed on the poisoned rats, received a secondary dose large enough to be lethal. The chain meant cat numbers could be reduced in a way that trapping alone had never achieved.

Jennifer Ross, the Department of Conservation’s Rakiura Operations Manager, described the outcome. “We managed to reduce feral cats to very low levels in the operational area,” she said. “This protected adult birds while they nested and raised their chicks on the mountain tops.”

The numbers behind that protection are striking. Of the 97 previously known adult birds in the operational area, 91 survived the breeding season — a survival rate that would have been unthinkable under normal predation pressure. Researchers also banded 56 juvenile birds, an unusually large cohort of young birds making it through to the point where they could be individually tracked. Those juveniles represent the next generation of a population that has been treading water for a generation.

For Ngāi Tahu, the iwi with kaitiakitanga over Rakiura, the result carries significance well beyond birdwatching. The pukunui is among a list of taonga species whose health and presence on the island is understood as a measure of its broader ecological mauri. Dean Whaanga, speaking on behalf of Ngāi Tahu leadership, framed the moment in those terms. “It’s critical we continue to take action, not just for pukunui, but to uplift the mauri of Rakiura and enable other taonga species like kākāpō and tīeke to safely return,” he said.

The operation was not without unintended consequences. White-tailed deer, a popular quarry for hunters on Stewart Island, were not a target species but proved more susceptible to the 1080 application than modelling had predicted. In standard bait areas, the deer population fell by around 97 percent. In zones where deer-repellent bait formulations were used, the reduction was still around 75 percent. Four dead deer were found in the aftermath of the operation.

Adam Fairmaid, president of the Rakiura Whitetail Trust, sought assurances from the Department of Conservation following the results, calling for clarity on how future operations would account for the deer population’s viability. The tension between predator control and the interests of recreational hunters on the island is not new, but the scale of the deer impact from this particular operation has brought it into sharper focus.

The 1080 debate in New Zealand rarely produces simple agreement. The compound is lethal to a broad range of mammals, its use in aerial operations is tightly regulated, and its supporters and critics have argued the evidence back and forth for decades. What the Rakiura results add to that ongoing conversation is a concrete outcome — a threatened bird that has struggled for thirty years recorded its best year on record, driven by an intervention that had not previously been tried at scale in its habitat.

The pukunui’s path to 300 birds by 2035 will require the gains from 2025 to be sustained and built upon. Whether that means repeat aerial operations, expanded coverage beyond the current 40,000 hectares, or new methods not yet tested, the Department of Conservation and its partners have not yet outlined a confirmed schedule. What they can point to now is evidence that, under the right conditions, the trend can reverse.

Originally reported by RNZ.

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