Milestones for island eradications
In the last month, two significant rodent eradications have been
declared a success - one on South Georgia and the other closer
to home, on the sub Antarctic Antipodes Islands.
was declared rodent-free in
early May with the island now clear of rats and mice. The
project is the world’s biggest to eradicate an invasive species
- the island is about 160-km-long, covering about 350,000 ha, with
about 100,000 ha ice and snow free.
Rats and mice were inadvertently introduced to the island 250 years
ago by passing ships that called in. The effect on native bird
populations was dramatic, as unused to predators, they laid their
eggs on the ground or in burrows, easily accessible to the rodents.
Two species of birds endemic to the island, the South Georgia pipit
and pintail, were largely confined to a few tiny islands off the
coast, which the rodents could not reach, and penguins and other
seabird populations were also threatened.
Aerial and ground based poison was laid over three seasons, ending
in 2016. Thousands of peanut butter-coated chew sticks, camera traps
and tracking tunnels were checked and New Zealand dog handlers
and three rodent detection dogs spent months on South Georgia
walking over hundreds of kilometres across the island looking for
any signs of rats and mice - and finding none.
The project has been heralded as an
inspiration for eradications on other large islands around the
New Zealand conservation dogs checked
South Georgia for signs
of rats and mice. Photo: Oliver
Prince/South Georgia Heritage Trust
Meanwhile on the
Islands, 750 km
southeast of New Zealand, the Department of Conservation officially
declared the island free of mice in March this year. The ‘Million
Dollar Mouse’ project aimed to eradicate mice , the only mammalian
predator, from the islands and set about aerial baiting in the
winter of 2016. Two seasons of breeding in were then needed to
determine if the islands were mice free. Like on South Georgia, the
team used a variety of monitoring methods as well as dogs to check
for signs of mice.
The Antipodes Islands are the only home of the Antipodes Island
snipe and the Antipodes Island parakeet, both of which nest on the
ground and are set to benefit greatly from the eradication.
New Zealand seabird relocation
Nearly 100 mottled petrel chick have been moved over 1,000km from
their home on Codfish Island to mainland New Zealand - inland
on the Maungaharuru Range in Hawke’s Bay. Like so many of New
Zealand’s hill country, the Maungaharuru Range once was home to
millions of seabirds.
The relocation in March was the biggest ever attempted and is part
of a broader plan to help seabirds repopulate the region.
The mottled petrel (kōrure)
will spend four to six weeks at the site where they will be
monitored and fed to bring them into optimal condition for fledging.
Kōrure, like many seabirds, were ecologically
important as natural recyclers of nutrients from the sea into native
Seabirds usually return to their natal nesting site—where they were
born—to breed, often several years after emerging from their burrows
will spend three to four years at sea before (hopefully) returning
to Maungaharuru to nest. Running since 2014, the relocation
programme has seen the first kōrure
returning to the site.
Kōrure, like many seabirds, were ecologically important as natural
recyclers of nutrients from the sea into native bush.
Korure or mottled petrel is endemic to
New Zealand and currently only breeds at a few sites in the south of
the country. Photo: Department of Conservation
Update from Lord Howe Island
The Lord Howe Island Rodent Eradication Project aims to eradicate
ship rats (Rattus
rattus) and mice (Mus
successful, Lord Howe Island would be the largest inhabited island
in the world where rodents have been eradicated.
Delay to 2019
In March 2018, the Lord Howe Island Board decided to delay the
baiting implementation phase of the project to winter 2019. The
decision to delay related to delays with receiving permits and
a change in the proposed method to increase bait stations in the
settlement area in response to community consultation. The change
needed more time and resources during the eradication and more time
invested in planning.
The overall baiting approach includes aerial broadcasting over
uninhabited parts of the island and a combination of hand
broadcasting and bait stations in the settlement area. The
actual treatment method over individual properties is to be
discussed and negotiated with individual leaseholders and residents
through property management plans.
Fish behaviour towards placebo bait pellets
Professor David Booth, Professor of Marine Ecology at the University
of Technology Sydney, has been studying the potential effects
of baits entering the ocean adjacent to Lord Howe Island
during the eradication. The study looked at the response of fish to
Placebo pellets (no toxin) were dropped into the water and fish
behaviour towards the pellets observed i.e., whether they ignored,
approached, mouthed or swallowed the baits. About 400 fish
were observed where pallets were dropped. About 37% totally ignored
the pellets, 36% approached but deflected the pellet, and 25%
mouthed the bait and then rejected it. Less than 2% of fish
swallowed the bait, all of which were at sites where people hand
feed fish (and where no aerial baiting would occur). The study
concluded that aerial application of bait would have little or no
effect on fish in areas adjacent to aerial baiting operations.