Razza, a brown Norwegian rat,
led scientists on a 'rat race'
of epic proportions.
 

Like a furry Robinson Crusoe, the brown Norwegian rat was cast away and left to fend for himself in an experiment New Zealand researchers say has given insight into why it's so hard to eradicate vermin from fragile island ecosystems.

For 18 weeks, Razza sidestepped countless traps and turned up his nose at poisoned bait before eventually plunging into the South Pacific and paddling 400 yards in open water to a new island in search of love, according to research published in this week's issue of the journal Nature.

The study was motivated by the need for conservation "because of the problems of rats on islands and rats reinvading islands that have been cleared," author Mick Clout of the University of Auckland's School of Biological Sciences told The Associated Press on Thursday.

"We wanted to test how difficult it would be to catch a single rodent using the standard methods of elimination (used for) for higher density populations," he said.

At least 11 New Zealand offshore islands cleared of rodents have been reinvaded in the past two decades.

Despite being weighed down by a tiny radio transmitter collar, Razza eluded intensive efforts to trap him during his 10-week sojourn on New Zealand's uninhabited and forested Motuhoropapa Island.

During that time, the rat evaded an arsenal of traps and poisoned baits that included peanut butter. He even continued to stay one step ahead of sniffer dogs sent in to track him down.

Then he disappeared only to turn up on neighboring Otata Island after his dip, apparently motivated by primordial urges during the spring-summer mating season, Clout said.

Researchers believe Razza's island-hopping journey was the longest confirmed swim by a rat.

"If this had been a pregnant female rat it would have been a problem," Clout said. "It takes only one ... to establish a population."

The saga didn't end there. Scientists spent eight more weeks trying to eliminate the ever-elusive invader on the second island.

"We were literally tearing our hair out at times trying to find this animal," Clout said.

New Zealand Department of Conservation scientist David Towns said the findings raise a series of issues over trying to protect threatened species on predator-free offshore sanctuaries.

The country's indigenous plants and animals often have ineffective defense mechanisms to ward off newly introduced species. Rats and possums have wreaked havoc on some islands.

New Zealand conservationists are using one rodent-free island to establish a colony of highly endangered plump and flightless green parrots called kakapos, according to the department's website.

"We didn't know it would be this difficult to trap (one) rat," Towns said, adding that rat-sniffing dogs ended up being the key to Razza's demise.

Only after they picked up the trail was the research team able to saturate the area with traps. The lure of fresh penguin meat was finally what ended Razza's 18 weeks on the lam — he was killed in the trap.

The scientists have since released another solo male rat with radio transmitter on the rodent-free 23-acre Motuhoropapa Island to make sure Razza's race wasn't a fluke.

"We want to check whether this (Razza) was normal behavior," Clout said.