For nearly five months, he led his pursuers a merry dance, swimming nearly half a kilometre across open sea to a new home, laughing at the traps and the poisoned baits and the baying hounds bent on killing him.

When the annals of rodentology are written — as they surely must — this rat deserves an honoured place.

His Rasputin-like feats, redolent of the Russian mystic who likewise sneered at efforts to bump him off, were described on Thursday by New Zealand conservationists.

Their extraordinary campaign to get rid of the rat, the only rodent on a remote island, was reported in the British weekly science journal Nature.

Wildlife officers in New Zealand wage a relentless war against rats and other introduced predators that decimate populations of the kiwi and other unique native species.

In November last year, the researchers used a chocolate-baited trap to capture an adult male Norway rat on the uninhabited, forested island of Pakihi, off north-eastern New Zealand.

Seeking to find out more about how lone rats move around and survive, they took a DNA sample from the creature’s tail, fitted a radio collar and then released it on a beach on another uninhabited but rat-less island, Motuhoropapa, 30km away.

For the next four weeks, there was no problem.

The tracker collar obligingly did its job, showing that the rat traversed the entire island, eventually settling down to a home territory of about a hectare.

After that, the conservationists tried to recapture the rat, setting nearly three dozen traps, deploying two trained dogs and digging 15 tracking tunnels to tip them off to his whereabouts.

Everything, dismayingly, failed. But worse was to come.

Somehow the radio signal got turned off. Out there, unchallenged and undetectable in the gloomy green, was a long-whiskered, sharp-toothed Rattus norvegicus.

Eventually, the trail was picked up again — not on Motuhoropapa, but on the neighbouring island of Otata.

Rat faeces found on this island were tested for DNA, and proved to come from the original rat, which had swum a whole 400m across open sea to find a new home.

Short of razing Otata with napalm, the full forces of human ingenuity came into play — a grid of bait stations and tracking tunnels was set up, another five traps were cunningly buried in the ground and 20 traps were set with peanut butter as bait.

Nemesis came after 18 weeks of freedom.

Tracker dogs picked up a strong patch of rodent scent, and it was there that the conservationists uncloaked the finest weapon in their arsenal, exceptional bait for an exceptional beast: a juicy chunk of penguin.

Rasputin’s demise is science’s gain, though.

Until now, field studies have focused on the risk of high-density populations of rats, in which juveniles escape because of competition for food and territory.

This is the first research into a single rat — and shows that a lone rat may behave quite unexpectedly, taking the risk of crossing open water to a new home even when its existing habitat is full of food and without predators.

“Eliminating a single invading rat is disproportionately difficult, not only because of atypical behaviour … but also because bait can be less effective in the absence of competition for natural food resources,” says lead author James Russell, of the University of Auckland’s department of conservation. — AFP