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Map of South Georgia IslandThe Globe and Mail

Tony Martin doesn't look like someone capable of killing millions of rats and mice.

The mild-mannered zoologist normally spends his time teaching animal conservation at the University of Dundee in Scotland. But for three months this year, Prof. Martin led the largest and most complicated rodent extermination ever attempted in the world.

The project was on South Georgia, a 160-kilometre-long island off the coast of Antarctica that is famous for the expeditions of Sir Ernest Shackleton who died there in 1922. The British territory is home to a variety of seals, seabirds and about 400,000 King penguins. It's also infested with millions of rats and mice, brought there by ships during the heyday of the whaling and sealing fishery in the early 1900s. Over the years, the rodents have systematically wiped out large parts of the seabird population, mainly by eating the chicks in their nests.

There's a lot at stake beyond the remote outpost of South Georgia. Rats and mice have become one of the biggest threats to wildlife on the planet, thanks to centuries of shipping, which has brought the hardy creatures to just about every corner of the world. Global warming has also opened up more space for them to invade as glaciers recede and climates become more hospitable. If Prof. Martin and his team could succeed in killing South Georgia's rodents on a mass scale, the extermination techniques could be used elsewhere.

"The biodiversity of the world, generally, is being lost more as a result of [rodents] than anything else other than habitat destruction," Prof. Martin told reporters in London this week during a presentation on the South Georgia program. "Rats are fantastic predators and the wildlife on islands around the world has evolved over millions of years in the absence of mammalian predators. Rats come along and in the space of a remarkably short time – sometimes weeks, certainly a few years – they can destroy everything that is vulnerable."

On South Georgia alone, rats and mice have nearly eliminated several avian varieties of pintails, petrels and pipits, some of which are found nowhere else. Glaciers on the island have also been receding at a rate of one metre a day, meaning the rodents are covering an even greater territory and attacking more small seabirds that nest on land. "It's a race against time," Prof. Martin added.

Rodent extermination on a large scale has been tried before, mainly on islands in the south Pacific. But it didn't work because the poison proved ineffective or wasn't spread out properly. And, in this type of quest, there is no room for failure.

"If we've killed 99.999 per cent, we have failed," Prof. Martin said. "If you leave one pregnant female or a pair, of course, very quickly – because we all know how rapidly rodents breed – they will be back to where they were."

Prof. Martin began work on the South Georgia project in 2009, teaming up with a group from the South Georgia Heritage Trust, a non-profit organization set up in 2005 to manage the island's conservation programs. He'd been fascinated with the place for years and dreamed of eliminating its lethal intruders. "As far as a legacy goes, this is the single thing that I can do that's going to have the biggest bang," he said.

The group did a trial run in 2011, using a helicopter to cover a small part of the island with about 58 tons of rat poison. The results were promising with later checks showing the area was rodent-free. South Georgia's topography helps. Glaciers cut off sections of the island, trapping rodents in some areas which makes it easier to wipe them out without fear of others moving in from elsewhere. The harsh climate is also beneficial since there are no other land animals likely to eat the poison.

But, now they had to kill off the rest. In February, 2013, Prof. Martin and a crew of 24 – dubbed "Team Rat" – began spreading poison pellets along the coastline, where seabirds and rats mingle. They covered 580 square kilometres with three helicopters, making 2,000 flights and working in extreme conditions including winds of up to 150 kilometres an hour, freezing temperatures and regular snow storms. They finished in mid-May, just as the winter season was about to start.

Prof. Martin and the team now must wait to see if it worked. They plan to return next year to check, but it could be years before a firm assessment can be made and bird populations return to normal levels. Meanwhile, there are concerns the growing number of tourist ships heading to the island to watch the penguins might bring along rats, nullifying the entire effort. Prof. Martin said precautions for tourist ships have been put in place and there are already signs bird numbers have started to increase in the 2009 trial area.

None of this was cheap. With its unforgiving climate and forbidding landscape, South Georgia is not easily accessible. There is no infrastructure and no permanent population, other than a handful of scientists during summer months. Everything, including the helicopters, had to be sent by ship from the Falkland Islands, which is about 1,400 kilometres away. The total cost of the project was $12-million (U.S.), which came largely from donations and grants from charitable foundations in Britain and the United States. That is unusual for conservation programs this size which usually get most of their money from government.

Whatever the project's success, Prof. Martin is already facing difficult ethical questions. How can a scientist who specializes in animal conservation condone the mass slaughter of any animal, even rats? "The choice is not, do you want to go out and cause death to a lot of rats?" he said defiantly. "The question is: Are you prepared to accept that millions of sea-bird chicks will have their brains eaten out while they are alive? Or will you take the opportunity that you have to kill a relatively small number of rats and stop that for all time?"

He added firmly: "I feel very strong, that man should try to put right the damage that he has done. And that's what we're doing."