Rasputin the Elusive Survivor Rat

Rattus norvegicus
Norway brown rat

Sci-Tech Today
Wednesday 19 October 2005

Rat Leads Humans
on Wild Goose Chase

(Agence France-Presse) -- His Rasputin-like feats in trying to escape New Zealand wildlife officers, redolent of the Russian mystic who likewise sneered at efforts to kill him, were reported in the British weekly science journal Nature. The rat's elusiveness challenges longstanding assumptions about the species' behavior.

For nearly five months, he led his pursuers a merry dance, swimming nearly a quarter of mile 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, this rat deserves an honored place.

A Rat With No Name

New Zealand wages a relentless war against rats and other introduced predators that decimate populations of the kiwi and other unique native species. In November 2004, the researchers used a chocolate-baited trap to capture an adult male Norway rat on the uninhabited, forested island of Pakihi, off the northeastern shore.

Seeking to find out more about how lone rats moved around and survived, they took a DNA sample from the creature's tail, fitted a radio collar and then released the creature on a beach on another uninhabited but rat-less island, Motuhoropapa, 18 miles away.

For four weeks, 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 (2.5 acres). 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.

He's Gone Rogue!

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 droppings found on this island were tested for DNA, and proved to come from the original rat, who had swum a whole 440 yards across open sea to find a new home.

The full forces of human ingenuity came into play as scientists sought to bring the rat in for questioning. They set up a grid of bait stations and tracking tunnels. Another five traps were cunningly buried in the ground and 20 traps were set with peanut butter as bait.

After 18 weeks, nothing.

The Hunt Finally Ends

Eventually tracker dogs picked up a strong patch of rodent scent, and it was then that the conservationists were able to end the chase, using a trap set with a juicy chunk of penguin.

Rasputin's loss 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 behavior ... 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.

© 2005 Agence France-Presse. All rights reserved.