Plague over: How this island has almost eradicated rodents

Lord Howe Island within whiskers of wiping out all rodents

National News
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How did they do it?

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Dr Terry O'Dwyer releasing a woodhen after captive management for the duration of the rodent eradication project. Photo: Supplied

Dr Terry O'Dwyer releasing a woodhen after captive management for the duration of the rodent eradication project. Photo: Supplied

As mice numbers rise to concerning levels on the mainland, Lord Howe Island is celebrating the believed eradication of hundreds of thousands of rodents which have plagued the idyllic isle since the late 1800s.

A long-planned for, $15.5 million, baiting program was conducted from June to October 2019 and it has now been 15-months since a rodent was detected on the island.

Visiting the island last week, NSW Environment Minister Matt Kean said he was delighted with the success of the program.

"This is an extraordinary example of a community conservation effort backed by world leading science," Mr Kean said.

"Feral pests and weeds have wreaked havoc here in the past. This program is reversing that and changing the destiny of the plants and animals that call this precious and unique part of Australia home."

Department of Planning, Industry and Environment senior scientist Dr Terry O'Dwyer has been involved with the eradication program since 2016.

Dr O'Dwyer said the impact rodents had on the environment of Lord Howe Island was marked from the outset.

"There were five species of birds that went extinct soon after rats were introduced in 1918, and probably untold invertebrate extinctions but no one was monitoring those," Dr O'Dwyer said.

"They also had a large impact on vegetation, because they eat seeds and seedlings.

"In some places in the forest you would notice there was no regrowth, only mature trees, as the forest aged nothing would be taking its place."

It has been estimated that there were up to 300,000 rodents on island at one time, but despite the impact they had on the environment, an eradication program was a divisive issue in the community for many years.

'The referendum'

A poll, known on the island as 'the referendum,' took place in 2015, with 52 per cent of people voting to go forward with an eradication program.

"People were concerned that we might kill non-targeted species through the baiting program," Dr O'Dwyer said.

"But, we did a lot of background research, identified species which may be at risk of secondary poison or directly eating the baits."

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Dr O'Dwyer said the endangered Lord Howe woodhen and Lord Howe currawong were identified as species at risk during the baiting program and as a consequence they were taken into captivity for the duration.

"They were kept in purpose built enclosures and looked after by Taronga Zoo staff on the island," Dr O'Dwyer said.

"They were released when it was deemed safe following monitoring of the bait breakdown."

Around the settlement area of the island and in paddocks with livestock bait was put in baiting stations to ensure it didn't impact other species, while more uninhabited parts of the island were aerially baited.

"The team who coordinated that did a great job, bait stations had to be refilled in a constant cycle every week to 10 days," Dr O'Dwyer said.

"There were 23,000 bait stations, constantly having to be cleaned out and refilled."

Record woodhen survey

The result has been worth it - a recent survey recording over 440 woodhens, twice the number recorded from just 12 months prior and significantly breaking the previous record of 250 birds.

Dr O'Dwyer said they have to wait two years before declaring a complete eradication but signs are very promising.

However, unfortunately the successful program would be hard to replicate on the mainland with isolation of an area near impossible.

"The area to bait would be huge and the non-intended targets which would eat the bait would be significant, so it is much more difficult but New Zealand has big plans," Dr O'Dwyer said.

The story Plague over: How this island has almost eradicated rodents first appeared on The Land.

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