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Razza the Nonnative Rat Wins Round 1

October 22, 2005|Alex Raksin | Times Staff Writer

A common brown sewer rat released on a deserted island in New Zealand outsmarted a team of researchers for four months, evading capture even though he was wearing a radio collar that let them track his movements.

The half-pound rat, nicknamed Razza, was set free on the island so researchers could test methods of trapping nonnative animals, according to their report in the current issue of the journal Nature.

Rats and other invasive species have wreaked havoc on many once-isolated island ecosystems, and eradicating such species has been priority for conservation biologists.

New Zealand Department of Conservation scientist David R. Towns said the team of researchers had assumed they could trap Razza within a few days of his release on Motuhoropapa, a forested 23 1/2 -acre island.

Instead, the rat carefully circled the island for three days, then settled on a 2 1/2 -acre home range in the fourth week.

Increasingly flummoxed, the researchers began laying traps at double the usual density, but Razza dodged those too. Then, in his 10th week of freedom, he disappeared altogether when the battery in his radio collar died.

Two weeks later, residents on Otata, an island 438 yards away, reported seeing birds behaving oddly as they had a few years earlier when the island had been invaded by rats. There, the team found rodent droppings that matched Razza's DNA and set up new traps.

Razza's swim to Otata is the longest recorded for a rat, the researchers believe.

Six weeks later, Razza was finally caught and killed in a trap baited with fresh penguin meat in an area where trained dogs had detected concentrated rodent scent.

"We may have had our fancy theories and radio telemetry, but it was the dogs that solved it for us," Towns said.

The researchers recently released another male rat on Motuhoropapa to see if Razza's long survival was a fluke.

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