Natural born killers stalk Kiwi birdlife

Stoats have wreaked havoc on the birds of New Zealand. Now conservationists are fighting back

By Kathy Marks

In Britain, stoats are part of the rhythm of nature. They prey on rabbits and rats; they are preyed on by foxes and eagles. In New Zealand, whose only land mammals were two species of bats until Europeans arrived, stoats are the single biggest threat to the unique and increasingly threatened native birdlife.

 

A world leader in conservation, New Zealand has saved some of its rarest birds from extinction by ridding off-shore islands of predators. Stoats, which can swim, were thought to have a maximum range of 1.5 kilometres (less than a mile). Recently, though, the sleek, furry killers have turned up on an island more than five kilometres from the mainland, raising questions about the safety of offshore sanctuaries.

Many of New Zealand's birds live and nest on the forest floor. Some, such as kakapo, weka and kiwi, are flightless. When they feel under threat, they freeze, making them easy prey for animals such as rats, cats and ferrets. Stoats – introduced in 1884 to combat a rabbit plague – are particularly formidable predators. They can tackle animals 10 times their body weight; they hunt by day as well as at night; they can travel vast distances, climb trees, and survive in almost any habitat. They are also prolific breeders, and they kill far more than they need to satisfy their hunger.

"When stoats get into a seabird colony or chicken hutch, they kill everything," says Andrew Veale, an expert on stoat genetics at Auckland University. He cites credible reports of a moorhen being attacked by a stoat and taking off into the air, with the stoat still attached. Dr Veale says: "They are phenomenal killers, with an immense bite strength."

More than 80 of New Zealand's offshore islands are pest-free sanctuaries where all mammals have been removed through trapping, shooting, and dropping poison from helicopters. Last year, a stoat was found on Rangitoto Island, more than three kilometres off Auckland. The island had been declared predator-free only a year earlier, following a NZ$3m (£1.6m) eradication programme. By analysing the stoat's DNA, Dr Veale established that it was from the mainland. This year, three stoats have been trapped on Kapiti island, a wildlife reserve 5.2 kilometres off Wellington. Dr Veale believes a female swam over and gave birth.

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