Nature's lean, mean killing machine

By Geoff Cumming

Andrew Veale's research aims to get a clearer idea of migration patterns, leading to more successful stoat eradication campaigns. Photo / Natalie Slade
Andrew Veale's research aims to get a clearer idea of migration patterns, leading to more successful stoat eradication campaigns. Photo / Natalie Slade

Like all great hunters, Andrew Veale has the utmost respect for his foe.

That the Auckland PhD student's quarry is a stoat in no way lessens the chase - nor the value of the prize.

Stoats represent the biggest threat to New Zealand's surviving native birdlife. They account for more than half of kiwi deaths outside "pest-free" sanctuaries and their preferred diet extends to weka, takahe, kaka, tui, bellbirds and others.

They are killing machines - 30cm of lean muscle, sinew and teeth adapted to tackle prey many times their size and bodyweight, says Veale. They kill far more than they need to satisfy short-term hunger - just in case food runs short tomorrow. And when they've cleaned-out one habitat, they find another.

"I don't think anyone can ignore their power and charisma," says Veale. "They have amazing muscle strength - I believe their bite strength is the highest of any mammal. I really respect them."

Wily and highly mobile, stoats are a more difficult menace than rats; their diet consists of fresh meat and eggs - they ignore pellets.

Stoats are one reason the Department of Conservation and volunteers put so much effort into clearing offshore islands of predators to establish sanctuaries for threatened birds.

But re-invasions of these islands by stoats and rats are a huge threat not just to birdsong but to ongoing support and funding. "A lot of money is invested in eradication campaigns. If they fail, morale goes down and the money dries up."

What's happened in the past year has not exactly boosted confidence that this is a battle environmentalists can win. But laboratory research by Veale and others using stoat DNA could help to tilt the balance back in favour of the conservation effort.

Based at Auckland University's Tamaki campus, Veale uses the adjoining Landcare Research lab to carry out DNA analysis of stoats trapped on the mainland and coastal islands. The aim is to build knowledge of different population structures and get a clearer idea of migration patterns, leading to more successful eradication campaigns.

The 28-year-old grew up tramping and mountaineering and got involved in island restoration work as a student.

A masters in population genetics (comparing populations of marine invertebrates) led to an invitation to help with research into stoats trapped on Sanctuary and Resolution islands off Fiordland - large islands with great potential for birdlife if they can be kept predator-free.

Last month, the Auckland Council granted $30,000 to help Veale continue his research and broaden his focus to the Hauraki Gulf. It's work which melds his scientific knowledge with his passion for conservation.

"I'm studying basically the most charismatic of species. They are amazing looking, can swim vast distances and kill everything when they get there and still look cute."

By comparing genetic variations between stoats found in the Hunuas, the Waitakeres, northern parks and on Hauraki Gulf islands, he hopes to establish how populations are connected. "We need to know the genetic structure of a population so that, if a stoat turns up somewhere it shouldn't, then we know where it's from. That can help with mitigation strategies."

Information about size, rates of increase and movement patterns of different populations should lead to more cost-effective control.

He can get stoat DNA from hairs left in traps and tunnels, even dead birds. But he prefers fresh tissue - his test tube collection of ears and tails is a highlight.

There are 600 stoats in his freezer. "Word has gone out - if you are catching stoats, send them to me."

He shares the vision of kiwi, weka, kaka and kakariki thriving, even on highly populated islands like Waiheke. "That would be amazing." And with new technology including self-resetting traps and targeted poisons, he believes it's possible to get the gulf islands largely pest free.

After a highly controversial $3 million eradication programme in 2009, Rangitoto and Motutapu islands were thought predator-free. But in July last year, a stoat was trapped. How did it get there?

Veale established through DNA analysis that it had come from the mainland, possibly by swimming at least 3km. This is more than twice the distance scientists thought stoats could swim. The news got worse in February when a stoat first sighted last December was trapped at the Kapiti Island wildlife sanctuary - 5km offshore.

Two further stoat trappings on Kapiti in the past month confirm a breeding population has established - an outcome devastating for conservationists as well as the birds. The multi-agency response - from intensive baiting and trapping to lab research - will cost hundreds of thousands of dollars. "It's scary. Kapiti was thought completely safe," says Veale. "Kapiti was the most pristine wildlife sanctuary that the public can access. Now, it has lost its predator-free status."

How vulnerable are the residents? He cites the hit-rate of a single male stoat on Motuotau Island, off Mt Maunganui, which killed 97 petrels in just three-weeks. "There have been several instances where a single stoat has swum to an island and an entire population of saddlebacks has been exterminated."

Veale doesn't blame the stoat, brought here in the late 19th century to combat rabbits. Naturally they found ground-dwelling birds which had evolved in a predator-free environment - and those that call from their nests - much easier prey.

Stoats are not only voracious killers, they breed and multiply like, well, rabbits. Young females are impregnated before they leave the nest and carry offspring in pre-embryonic form for months before giving birth in spring. "There's no such thing as a female stoat that's not pregnant," says Veale. "They are the perfect invader: any female that gets to an island can start a population."

Luckily, the Rangitoto find was a one-off and a male.

Further sampling of mainland stoats may allow Veale to establish where it came from, allowing a targeted eradication effort.

A possible migration pathway starts from the Hunuas, with nearby islands Pakihi and Ponui providing stepping stones to Waiheke and beyond. Even urban areas such as Takapuna may be launching points for stoats on Rangitoto, though currents could carry them from coastal parks further north.

What makes them swim?

"That's the question everyone asks and I would love to be a stoat psychologist. We know it's adults and juveniles, males and females, and it seems to be a year-round occurence. We think it's a food acquisition thing - if they don't have enough food they go swimming."

Getting the gulf islands to a pest-free state where birds can thrive is a huge challenge, with options limited on privately owned and populated islands such as Waiheke. "But if we can show we can get them off and keep them off using a scientifically designed programme - that's what biosecurity is all about. A large number of people would love to have kiwi, weka and kakariki on Waiheke."

He stresses his lab work is merely an add-on to the field work by DoC staff and volunteers, who do the hard yards trapping and rebaiting. But the information he gains could boost their chances of success.

"One of the biggest risks is failure. If you don't get it right the first time, support just wanes."


How you can help

* Report any stoat sightings to DoC

* Become a volunteer. For a list of conservation projects in your region, go to:

Other websites include:


- NZ Herald

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