How charity workers rid an entire Antarctic island of rats

South Georgia, a remote island off the tip of Antarctica, is teeming with penguins, seals, rare birds and — for about 250 years — millions of rats.

But now, after the world's largest rodent eradication project, the island is rat-free. 

The decade-long project was led by the Scottish charity South Georgia Heritage Trust.

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Over 10 years, members of "Team Rat" dropped rat poison from helicopters and used three rodent detection dogs to rid the British island of rats that had been devastating the wildlife. 

Dickie Hall is the habitat restoration project director who spent the last six months searching the island for rodents. He spoke with As It Happens guest host Helen Mann about the project.

Here is part of that conversation. 

Mr. Hall, you've been hard at work at this for a number of years now. How does it feel to have South Georgia island rat-free?

It feels absolutely fantastic. Somewhat unbelievable. 

We always hoped for the best, but we have to prepare ourselves for the worst. But in the end, we did the survey and no rodents were found.

Describe the island for us.

It's an incredibly mountainous place. It's only, I suppose, a hundred miles or so long, which doesn't sound massive, but it's like the Alps have been chopped off midway up and just dropped into the ocean.

And all around the edge of the island … are little patches and pockets of greenery and vegetation, and that's where most of the animals and bird life live.

And there were rats at one point. How did they get there?

So in the 18th century, the sealers and the whalers began to arrive at South Georgia partly thanks to Captain Cook who had sent reports back to Britain to say that this was a real haven for seals.  

And so all of these sailing vessels began to head down to South Georgia to harvest the seals and take the skins.

And in doing so, as was back then, these ships had rats on board. They were infested with rats.

And how big did the rat population become?

There were perhaps five million rats on the island.

That's an enormous task to get rid of that many rats.

It's an absolutely enormous task.

What was the effect that these rats were having on the natural wildlife?

The rats on the island were basically eating anything in sight.

I should explain that South Georgia is an island without trees. So any bird on the island nests on the ground or it nests under the ground and burrows.

That's right in the path of the rats, and it just becomes a free for all for the rats to eat the chicks and to eat the eggs.

What kind of steps did you have to take?

We adopted an approach that's been used widely by the New Zealanders, which is aerial baiting from helicopters.

We have helicopters flying across the island, following GPS lines and they spread baits from the air and we covered every inch of the island that way.

How did you finally determine that you'd gotten rid of them?

We put out rodent detection devices and we had dog handlers with rodent detection dogs and we scoured the whole of South Georgia.

Amazingly, thankfully, we found no evidence of existing rodents.

What about the poison itself? Any concerns about the impact it might have on other wildlife?

We had worked closely with the manufacturer of the poison and so it was it was designed and tailored to be attractive to rodents, but not particularly attractive to bird life.

That said, some of the birds are general scavengers and general browsers and they will potentially pick up some of the poison bites, and that was simply collateral damage that we had to accept.

Written and produced by Sarah Jackson. Q&A has been edited for length and clarity.