Rat's Tale Highlights Difficulty of Tracking a Pest

A Norwegian rat braves the waters of the South Pacific to escape a scientist hot on his trail. New Zealand rodent biologist James Russell went through epic efforts to track a member of a cunning invasive species.

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By some accounts, the greatest threat to rare plants and animals are invasive species. When these life forms get loose in defenseless ecosystems, it's often next to impossible to make them go away. If you're wondering why, try catching a rat that's just invaded an island. Recently, a team of scientists in New Zealand attempted just that. NPR's John Nielsen has the frustrating tale.

JOHN NIELSEN reporting:

Rats, especially Norwegian rats, are crafty little mammals. James Russell, a rodent biologist at the University of Auckland in New Zealand, says you can see it in their eyes.

Mr. JAMES RUSSELL (University of Auckland): When you look in that cage, they look back at you and they're just thinking, `You make one mistake, and I'm out of this cage and I'm gone.'

NIELSEN: Russell says this craftiness is partly why Norwegian rats have managed to invest more than 85 percent of the world's islands, wiping out innumerable wild birds and reptiles by gobbling up their eggs. In hopes of learning how to prevent these infestations, Russell and a team of radio trackers recently put a single Norwegian rat into a cage and took it out to an uninfested island off the coast of New Zealand. The plan was to follow the rat around after putting the cage down on the beach and opening it up. Instead, as soon as the cage hit the sand...

Mr. RUSSELL: He burst out of the cage through a crack in it. He was not impressed at all.

NIELSEN: Russell spent the next month trying to catch up with this experimental rat, which happened to have a radio tracking collar wrapped around its neck. He followed the beeping noises sent out by the collar, working every night from dusk to dawn, but he never once saw the rat. At most, he found pieces of nibbled bait.

Mr. RUSSELL: And you think, `Was that him?' And everyone would be phoning saying, `Have you done it?' and I'm just, `Nah. Nope. Nada.'

NIELSEN: Russell says he started having dreams about a disappearing rat. Meanwhile, his colleagues had started calling the real creature Razza, or the Love Rat.

This was not the way his experiment was supposed to be unfolding. And then it got worse. Russell and his team turned on their receivers one day and heard no beeping noises. Thinking the rat had swum into the ocean and drowned, they packed up and went home to New Zealand. There, they got a call from a couple visiting an uninfested island close to the first one. They'd just seen a live rat with a radio collar wrapped around its neck. Russell was stunned to hear that his rat had just swum through 400 yards of open ocean.

Mr. RUSSELL: When his little head's just 3 centimeters above the water, he's not going to be able to see where he's going, he's fighting currents and rocks and tide. And yet, he just says, `I'm here, I want to be there and I'm going to do it.'

NIELSEN: Russell and a team of trappers went straight to the island. They sent out teams of rat-sniffing dogs and set lots of traps. Three months later after finding nothing, they were ready to give up again. `The rat had won,' in Russell's words. This felt personal.

Mr. RUSSELL: He was mocking me. He was mocking me. He was saying, `Sorry, buddy, but I'm not going to do this your way. If you're chasing me and my life's on the edge, then I'm going to be running hard.'

NIELSEN: Then, a dead penguin washed up on the beach. Russell stuck it near a trap. He said he found the rat dead in that trap the very next morning. Did he feel sad? He pauses. `Nah.'

Mr. RUSSELL: It was more a, `Gotcha! You've outsmarted me for five months and been the butt of all my friends' jokes on me. And we got you in the end.'

NIELSEN: Russell tells his rat tale in the journal Nature. Based on what he went through, he says it will not be easy to catch these infestations early. John Nielsen, NPR News, Washington.

ELLIOTT: You're listening to ALL THINGS CONSIDERED.

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