Rats have infested this remote atoll near Tahiti, but an eradication attempt aims to turn back the clock

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On what should be a pristine tropical island, humans have introduced a destructive pest. Can scientists turn back the clock?

The French Polynesian island of Reiono looks like a postcard.

It's an uninhabited dot of land in the middle of the Pacific Ocean, home to a unique tropical ecosystem.

Because it's so remote and untamed, it's also a rare refuge for nesting seabirds.

In amongst the dense, humid wall of vegetation, red-footed booby chicks screech for food, while their parents skim across the lagoon. Black noddies and white terns chirp and whistle in the treetops.

But even here, on a tiny island with no permanent settlement, humans have left a mark.

Because when people arrived on Reiono, they brought rats with them.

Every afternoon, at almost exactly 3pm, thousands come out to begin foraging.

A destructive force

A seabird's unattended eggs are easy prey. A chick that falls to the ground at night has nowhere to hide.

Compared to its rat-free island neighbours, Reiono's ecosystem has suffered.

Ground-nesting birds have been forced off the island, and there are fewer smaller species here.

Some plant species have been completely devoured, and land crabs have to compete with the rats in the undergrowth at night.

All this destruction has drawn a visit from one of the world's top rat eradication experts.

Dr Araceli Samaniego is leading a project to kill off every single rat on Reiono.

"They are a huge problem," Araceli says.

"They have caused a lot of extinctions.

"A lot of these animals just never had to deal with this type of predation."

Rodents are notoriously resilient — they eat almost anything, and in warmer climates they can breed all year round.

This means many tropical island eradication attempts have failed.

Araceli's solution is to carpet every inch of Reiono with hundreds of kilograms of poison bait — all dropped on the same day.

"The best you can do is put the bait on the ground on the same day, covering 100 per cent of the island. No gaps at all.

"It is all or nothing. It takes one pregnant female to ruin all the planning."

This is not an exaggeration.

In 2011, a $2 million eradication attempt on Henderson Island in the South Pacific failed because just 60-80 rats survived.

Now, the population there has recovered to its original size of between 50,000 and 100,000.

"It has to be 100 per cent success," Araceli says.

But the remoteness of this island makes such an enormous project challenging.

Reiono is one of 13 tiny islands in the isolated atoll of Tetiaroa, about 60 kilometres off the coast of Tahiti.

The island, or "motu" as it's known to local Polynesians, is about 800 metres long.

Food, water, and supplies arrive by a tiny boat from a neighbouring island — but only when the weather is fair.

Araceli is living in a tent on the island for five weeks to coordinate the eradication.

Her field laboratory is a white tarp strung between pisonia trees, just back from the shoreline.

Know your enemy

Araceli is using the eradication as an opportunity to learn more about rat behaviour on tropical islands.

"We're going to track different aspects of the rats, from the breeding to the movement, to the ecology and the diet," she says.

Araceli is particularly interested in whether rats that have just had pups would still venture out of burrows to eat the bait — and whether they'd bring it back to the newborns.

If they don't, this could explain why eradication attempts on tropical islands have been failing.

So, part of the project involves tagging individuals with radio collars to track down their burrows.

They're also taking samples of the rats, and their poo, to map changes in their diet.

The work often involves traipsing through the forest at night, carrying handfuls of steel traps.

All of the information will help researchers design better baiting programs for other island ecosystems.

Araceli says Reiono will be a crucial test site for future eradications.

"It's really important we get this done, because we are not talking just about Reiono here," she says.

Prepare for eradication

As the day to drop the bait approaches, a handful of volunteers from a French Polynesian bird conservation group, and rangers from a local environmental protection group, arrive to help.

They're told the island is safe, except for one major hazard.

"A falling coconut can kill you — really," Araceli says.

So, they wear helmets for protection.

They get to work setting up a grid of colourful flags across the island, to make sure the 800 kilograms of bait is evenly scattered across Reiono.

It's clear Araceli has mixed feelings about killing off an entire species — even in this vulnerable ecosystem.

"I actually like them," she says.

"I respect them a lot because they are amazing animals. They're really flexible."

However, she says, humans introduced rats to places like Reiono, so it's only fair that we clean up the mess.

"It's because of us they are now all around the globe causing problems.

"It's our responsibility to do something about it, because we are losing species, especially on islands."

The poison — an anticoagulant that will stop the rats' blood from clotting — will be dropped right across every square of the newly laid island grid, all at once.

If there are any signs of rats after a few days, the team will follow up with a second island-wide drop.

Araceli says that the other animals on the island won't be affected; the land crabs will eat the bait, but the poison doesn't work on their blood.

A ray of hope

Several weeks after the bait drop, Araceli returns to the island to find out if the eradication was successful.

Only with the passage of time, and very thorough checking, can she and her team be sure that no rats have survived.

Finally, she's ready to share the good news.

"We are 99 per cent confident.

"Everything indicates that we are rat free — Reiono is rat-free."

Her laugh is tinged with exhaustion.

There will be follow-up checks on the island for years to come, but if the signs remain positive, Araceli says the success could pave the way for future attempts on other islands.

"It was a very special case, because it was an experimental eradication.

"It's very, very exciting."

As well as testing a successful eradication strategy, Araceli hopes that her team's work on Reiono will make it a stronghold.

A tiny haven, restored, and playing host to some of this region's most fragile species.

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Topics: science-and-technology, invasive-species, environment, environmental-management, conservation, environmental-impact, french-polynesia

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