Razza swam from one island to another 400m away

Razza avoided traps, escaped dogs, and ultimately swam a record distance from one uninhabited island to another.

Researchers from the University of Auckland in New Zealand had problems catching him even though they had fitted him with a radio transmitter.

He was finally killed by a trap 18 weeks after the experiment began.

The researchers released Razza to study "the problem of rats reinvading islands that have been cleared", author Mick Clout told the Associated Press news agency.

The research was reported in the scientific journal Nature.

Let loose on the uninhabited New Zealand island of Motuhoropapa, Razza ran free for 10 weeks before swimming 400m (1300ft) to a nearby island which was also deserted.

It is thought to be the longest swim across open water ever recorded for a rat.

Just lucky?

It then took the scientists another eight weeks to find and catch him once he arrived on Otata island.

"We were literally tearing our hair out at times trying to find this animal," Mr Clout said.

He said it was fortunate they had used a lone male rat in the experiment.

"If this had been a pregnant female rat it would have been a problem. It takes only one to establish a population."

Scientists have released a new male rat in a follow-up experiment to see if Razza was unusually clever or lucky.