Fugitive Rat Teaches Lesson About Invasive Species Control

Bethany Halford
for National Geographic News
October 19, 2005

It sounds like a plot from a Tom and Jerry cartoon: Intrepid hunters spend weeks on an island setting complex traps while their quarry evades them at every turn.

But this seemingly comic cat-and-mouse chase has grim implications for efforts to protect fragile island ecosystems from invasive species.

Conservationists from the University of Auckland wanted to get a better handle on how susceptible a solitary, island-invading rat is to conventional traps. They therefore intentionally unleashed a lone Norway rat upon New Zealand's rat-free Motuhoropapa Island.

The scientists suspected the animal might be more difficult to trap than a rat released in a city. After all, with an island full of food, the rat would tend not to snack on poisoned bait.

But they did not anticipate that this cagey critter would elude them for 18 weeks, eventually swimming across open ocean to a neighboring island.

The rodent's evasive maneuvers indicate that traditional traps might not be effective for catching the first arrival of an invasive species. The findings are reported in tomorrow's issue of the journal Nature.

Cagey, Not Caged

Invasive rodents, such as the Norway rat (Rattus norvegicus), are known to cause major disruptions to isolated ecosystems.

"Invasive animals are the single biggest threat to seabirds and island ecosystems," Bernie Tershy, executive director of the nonprofit organization Island Conservation, said in an e-mail.

"Preventing new introductions and eradicating existing populations of invasive animals is an incredibly effective conservation strategy."

"In parts of the world like New Zealand it's been recognized that [rodent invasions are] a big problem," said Mick N. Clout, a professor of conservation ecology at University of Auckland who co-authored the study with graduate student James C. Russell.

Although rats can be eradicated from islands, they tend to reinvade.

Continued on Next Page >>




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