Possums threaten far more than kiwi. Across Aotearoa, lesser-known species like whio, mohua, hihi and pekapeka are fighting for survival against possum predation and competition — and in many cases, winning, thanks to sustained predator control. The fur used in possum merino knitwear comes directly from this conservation work.
Most people know possums kill kiwi. Fewer know that possums sit on nesting birds and crush them, compete with native species for tree hollows, strip the canopy that entire ecosystems depend on, and have been caught on camera raiding nests in the dark. The kiwi, the kōkako, the kererū, the tūī — these are the species that make the news, and we've written about them before.
But there are species just as threatened, just as extraordinary, and far less talked about. Here are four of them.
Whio — the river duck you can't rescue
The whio is one of the few waterfowl species in the world that lives year-round on fast-flowing rivers. Slate-blue, fiercely territorial, and monogamous for life, it has adapted to an environment most ducks would avoid entirely — feeding on insect larvae in rapids, nesting on riverbanks, and navigating whitewater that would drown anything less specialised. It features on the New Zealand $10 note. There are fewer than 3,000 left.
Here's what makes the whio's situation different from most endangered birds: you can't move them to a predator-free island. Whio need large stretches of fast-flowing river habitat that doesn't exist offshore. Their survival depends on controlling predators in the mainland forests where they live. There is no Plan B.
Possums and rats raid whio nests for eggs. Stoats kill nesting females. During the late summer moult, whio are flightless — completely defenceless on the riverbank. In areas without predator control, there's a high prevalence of unpaired males, because the females are being killed on the nest faster than the population can replace them.
But the data from managed sites is clear. In Kahurangi National Park, whio numbers increased 48% after sustained predator control — from 29 pairs to 43. After aerial operations, duckling numbers jumped from fewer than 25 to 65 in a single breeding season. On Mount Taranaki, fledgling numbers climbed from 23 to 58 within two seasons. Same story at every managed site: control the predators, whio recover.
Mohua — the cavity nester that can't escape
In the 1800s, the mohua was one of the most abundant forest birds in the South Island — described as conspicuous and common, its call carrying through the beech canopy. Today there are fewer than 5,000, scattered across isolated pockets of South Island beech forest and Stewart Island.
The mohua nests in tree holes. This is the detail that defines its vulnerability. When a possum, rat, or stoat finds a mohua nest, the incubating bird — always the female — is trapped inside the cavity with nowhere to go. Predators don't just take eggs and chicks; they kill breeding females on the nest. The result is populations with a devastating skew: too many males, not enough females, and a breeding rate that can't keep pace with the losses.
In the Eglinton Valley in Fiordland, a stoat irruption in 1990 killed 43% of incubating female mohua in a single season. In the Hawdon Valley near Arthur's Pass, the population crashed to just 14 adults — only four of them female. On Mount Stokes in the Marlborough Sounds, around 90 birds were driven to local extinction by 2001, despite an active control programme, when ship rats overwhelmed the defences during a double beech mast.
Predator control works — DOC monitoring in the Dart and Routeburn valleys showed nesting success was twice as high after control operations. But the margin for error is razor-thin. A single bad mast year can undo decades of work. The mohua is a species that doesn't forgive a gap in the trapping schedule.
Hihi — the bird that belongs to no family
The hihi — also called the stitchbird — is one of the strangest birds in New Zealand, and that's a high bar. Until 2006, scientists thought it was a honeyeater, related to tūī and bellbirds. Genetic analysis proved them wrong. The hihi belongs to its own family, Notiomystidae, found nowhere else on earth. Nothing else alive is closely related to it.
It nearly didn't make it. By 1883, the hihi had vanished from the entire North Island mainland, wiped out by ship rats and habitat loss. For over a century, the only wild population clung to existence on Te Hauturu-o-Toi (Little Barrier Island), protected by the water that predators couldn't cross. There are currently around 2,000 hihi nationwide — every one descended from that island remnant or carefully managed translocations since.
Since 2005, conservationists have been reintroducing hihi to predator-controlled mainland sites. Zealandia in Wellington was one of the first, receiving translocated birds from Tiritiri Matangi Island. There are now managed populations at Zealandia, Bushy Park near Whanganui, Maungatautari, Rotokare, and Shakespeare Regional Park. But hihi are demanding tenants — they need complete predator exclusion, supplementary feeding at most sites, and nest boxes sprayed against mites that can kill chicks.
The hihi's conservation status has improved from Nationally Endangered to Nationally Vulnerable — a genuine win, built on decades of painstaking work. But every population outside of Little Barrier Island depends on ongoing management to survive. Take away the traplines and the feeding stations, and the hihi disappears again. That's the deal.
Pekapeka-tou-roa — not a bird at all
Most people don't know New Zealand has bats. It does — and they're the country's only native land mammals. The pekapeka-tou-roa, or long-tailed bat, is classified as Nationally Critical, the highest threat ranking in New Zealand's conservation system. It is closer to extinction than the kiwi.
Pekapeka roost in hollow trees — the same cavities that possums want. A single colony can use over 100 different roost trees across its home range, cycling between them regularly. You can't fence off a hundred trees scattered across a valley. And when predators find a roost, the consequences are immediate. At Rangataua near Tongariro National Park, a single feral cat killed 102 bats in one roost tree in one week.
Possums aren't the primary killer — rats and cats do more direct damage — but they contribute in a way that's harder to measure: by occupying the tree cavities that pekapeka depend on for roosting and breeding. Every hollow taken by a possum is one less roost for a species that reproduces slowly — one pup per year, per mother. Possums have also been observed attempting to catch bats at their roosts directly.
The turnaround where predator control is sustained has been dramatic. In the Eglinton Valley in Fiordland, long-tailed bats went from declining at 5% per year to increasing at 4% — a complete reversal built on trapping and poison bait stations maintained since the late 1990s. At Pureora Forest Park, short-tailed bats have grown at 10% per year. In 2025, DOC ran predator control operations across hundreds of thousands of hectares specifically listing pekapeka as a protected species — from Kahurangi to Pureora to Ruahine to Waipoua. And near Waiuku, south of Auckland, a five-year tracking project working with iwi Ngāti Te Ata Waiohua is studying bat movements in ways that have never been attempted before.
The pekapeka won Bird of the Year in 2021 — despite not being a bird. It was a publicity stunt that worked: more people know about New Zealand's bats now than at any point in history. But knowing they exist doesn't keep predators out of roost trees. Trapping does.
Why this matters
A river duck, a beech forest songbird, a honeyeater that isn't a honeyeater, and a bat. Four species with almost nothing in common except this: their survival depends on controlling the introduced predators — possums, rats, and stoats — that are pulling New Zealand's ecosystems apart.
The possum fur in possum merino knitwear comes from trappers doing exactly this work. No possums are farmed. The fibre is a by-product of conservation pest control — the same programmes that are bringing whio numbers up in Kahurangi, keeping mohua alive in Fiordland, giving hihi a foothold on the mainland, and reversing bat decline in the Eglinton Valley. Using the fur creates economic value that sustains the trapping network over the long term, and makes sure nothing from the work goes to waste.
Read more about the conservation story behind possum merino on our conservation impact page, or learn about the kiwi, kōkako, kererū and tūī — the species most people already know.
Sources
- Department of Conservation. "Blue duck/whio." doc.govt.nz
- Department of Conservation. "Great gains for blue duck/whio with DOC's predator control." Media release, June 2017. doc.govt.nz
- Department of Conservation. "Taranaki Mounga predator control a success." Media release, November 2019. doc.govt.nz
- New Zealand Birds Online. "Whio | Blue duck." nzbirdsonline.org.nz
- Department of Conservation. "Yellowhead/mohua." doc.govt.nz
- Department of Conservation. "Yellowhead/mohua monitoring: National Predator Control Programme." doc.govt.nz
- New Zealand Geographic. "Mohua in trouble." nzgeo.com
- Dilks, P.J. "Population growth following predator control in the Eglinton Valley, Fiordland." Notornis 46(3), 1999. birdsnz.org.nz
- Department of Conservation. "Hihi/stitchbird." doc.govt.nz
- New Zealand Birds Online. "Hihi | Stitchbird." nzbirdsonline.org.nz
- Zealandia Te Māra a Tāne. "Hihi | Stitchbird." visitzealandia.com
- Department of Conservation. "New Zealand long-tailed bat." doc.govt.nz
- Department of Conservation. "Long and short-tailed bat/pekapeka monitoring: National Predator Control Programme." doc.govt.nz
- Department of Conservation. "Predator control operations 2025." doc.govt.nz
- 1News. "Study underway to learn if bats can be used as 'agricultural tool'." January 2025. 1news.co.nz
