Their extraordinary campaign to get rid of the rat, the only rodent on a remote island, was reported in the British weekly science journal,
Nature.
Wildlife officers in New Zealand wage a relentless war against rats and other introduced predators that decimate kiwi populations and other unique native species.
In November 2004, the researchers used a trap baited with chocolate to capture an adult male Norway rat on the uninhabited, forested island of Pakihi off northeastern New Zealand.
Seeking to find out more about how lone rats move around and survive, they took a DNA sample from the creature's tail, fitted it with a radio collar and then released it on the beach on another uninhabited but rat-less island, Motuhoropapa, 30 kilometers (18 miles) away.
For the next four weeks there was no problem. The tracking collar obligingly did its job, showing that the rat traversed the entire island and eventually settled down to a home territory of about a hectare (2.5 acres).
After that, the conservationists tried to recapture the rat, setting nearly three dozen traps, deploying two trained dogs and digging 15 tracking tunnels to tip them off to his whereabouts.
Everything, dismayingly, failed.
But worse was to come. Somehow the radio signal got turned off. Out there, unchallenged and undetectable in the gloomy green, was a long-whiskered, sharp-toothed
Rattus norvegicus.
