Scientists employ rat-like cunning

Scientists are using crime-fighting technology to identify rats threatening native species by taking copies of their footprints.

White cards and ink pads are left in tunnels to collect the prints from passing rats. The cards are then put through a computer program that can tell the prints of different rat species apart, something human experts cannot do.

"We can understand patterns of invasion on predator-free islands, or detect new species entering New Zealand," James Russell, of Auckland University, said. "Footprint cards are a cheap way of identifying animals. They are particularly useful for monitoring animals in low numbers, or which are difficult for human observers to find."

Researchers hope to make the program freely available online, in the hope it will build a global database of rat species. "We are taking an open-source approach," Dr Russell said.

The Conservation Department and reserves such as Zealandia in Wellington already use print cards to identify harmful invaders, but the analysis is done manually.

"While experts can identify tracks of many animals, they are unable to differentiate between species with similar-looking footprints, like rat species," Dr Russell said.

New Zealand is home to three species of rat: the kiore, norway rat and ship rat. All have different behaviours and, if researchers know what they are dealing with, they can lay traps accordingly.

Ship rats, for example, can climb trees and norway rats prefer to live near water.

Zealandia spokesman Alan Dicks said the new method was interesting, but not of much practical use to the sanctuary, as ship rats were the only species living nearby.

The last rats known to have been at Zealandia were found in May last year.

It is hoped the new method will eventually be able to tell genders apart, something Mr Dicks said would interest the sanctuary.

"It's always handy to know if rats are male or female, as females are pregnant most of the time."

The footprint identification technique has already been deployed on Rangitoto and Motutapu islands near Auckland, where efforts are under way to get rid of introduced pests.

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