Download Macquarie Island: from rabbits and rodents to recovery and renewal

MACQUARIE ISLAND: FROM
RABBITS AND RODENTS TO
RECOVERY AND RENEWAL
A majestic landscape
Roughly half way between Tasmania and
Antarctica lies Macquarie Island. At approximately
34 kilometres long and 5.5 kilometres wide at
its broadest point, this subantarctic island is
renowned for the spectacular beauty of its remote
and windswept landscape. Its steep escarpments,
lakes, and dramatic changes in vegetation
provide an outstanding spectacle of wild, natural
beauty complemented by vast congregations of
wildlife including penguins and seals.
It also provides a unique opportunity to study
geological features and processes of oceanic
crust formation and plate boundary dynamics.
It is the only place in the world where rocks from
the earth’s mantle are being actively exposed
above sea level.
Macquarie Island’s inscription on the World
Heritage List in 1997 was in recognition of
its outstanding natural values. Its birdlife in
particular has always been extraordinary. The
breeding populations of penguins (including
the endemic royal penguin), albatrosses,
petrels and prions are recognised as one of the
greatest concentrations of seabirds in the world.
Royal penguins. (Photo: Greg Stone)
environment.gov.au
Images (L–R): Shield ferns. (Photo: Stephen Horn), Petrels nesting at Gadget Gully. (Photo: Chris Howard).
HER89.0613
Macquarie Island on a misty day.
(Photo: Richard Dakin)
Rabbit and rodent invasion
Eradicating the invaders
European rabbits were introduced to Macquarie
Island in the 1870s, while black rats and house
mice were first recorded on the island in the
1890s. Following the eradication of feral cats in
2000, rabbits and rodents became the dominant
pest species on the island. A dramatic increase in
their populations caused devastating damage to
the island’s vulnerable vegetation and wildlife.
The Macquarie Island Pest Eradication Project was
developed to eradicate all three invasive species
at the same time. In June 2007, the Australian and
Tasmanian governments agreed to $24.6 million
of joint funding to implement the Plan for the
Eradication of Rabbits and Rodents on Macquarie
Island. The plan was based on New Zealand’s
experience in successfully eradicating rabbits and
rodents from similar subantarctic islands.
Rabbits consumed the large leafy megaherbs
and grasses, which lacked the ability to adapt
to grazing. Extensive damage was occurring to
the tall tussock grassland, resulting in a loss of
breeding habitat for nesting seabirds and the
destabilisation of slopes. Rats had been preying
on seabird chicks and eggs, and were a threat to
at least nine bird species breeding on Macquarie
Island. The presence of rats and mice was also
inhibiting plant regeneration.
This important project required several years
of detailed planning, with management by the
Tasmania Parks and Wildlife Service. The project is
overseen by a steering committee which includes
representatives from the Tasmanian Government,
Australian Government and the New Zealand
Department of Conservation. The Australian
Government is committed to continuing the
success of the program.
Poison baits were dropped by helicopter in the
winter of 2010. The bait drop was carried out in
winter for three main reasons: to reduce the impact
on native wildlife, much of which leaves the island
during the winter; to target rabbits and rodents when
they were at their lowest numbers; and to increase
the likelihood of bait uptake by the target species
as there is less alternative food available. Around
eight per cent of the bait was distributed before bad
weather forced the postponement of the bait drop
to the winter of 2011. Rabbit and rodent activity
decreased markedly in areas that had been baited.
Effects of the rabbit population. (Photo: Image courtesy of
Tasmania Parks and Wildlife Service)
However, the number of seabird deaths following the
limited baiting was higher than estimated, primarily
due to poisoned rabbit carcasses being eaten by
scavenging seabirds. A review of the program found
that no entire population of seabird was expected
environment.gov.au
Images (L–R): Galium
Shield ferns.
antarcticum.
(Photo: (Photo:
StephenNick
Horn),
Fitzgerald),
Petrels nesting
Track protecting
at Gadgetsensitive
Gully. (Photo:
vegetation.
Chris Howard).
(Photo: Chris Howard)
Aerial baiting was completed in the winter of 2011
and was supplemented with a limited amount of
hand baiting. Ground hunting teams made up
of skilled hunters and specially trained detector
dogs worked to eliminate surviving rabbits. The
dogs were trained to locate rabbits but not to harm
native animals. In addition, three specially trained
rodent detector dogs were sent to the island in
March 2013. Ground hunting teams have now
covered over 65 000 km on foot since August 2011
looking for signs of rabbits and rodents.
Revegetation and renewal
King penguins and detector dogs. (Photo: Dana Boyte)
to be lost as a result of the continuation of the
project. It also found that if the eradication program
was not continued catastrophic damage to the
ecosystem would continue and some seabird
populations could become extinct on the island.
The eradication program was subsequently
modified to lessen the impact on native wildlife.
Calicivirus was introduced early in 2011 with the
aim of reducing the rabbit population and the
number of poisoned rabbit carcasses following
baiting. More people were employed to search the
island and remove poisoned carcasses before they
could be consumed by scavenging seabirds.
Although the program has not yet been completed,
great progress has been made with both the
eradication of pests and the recovery of vegetation
species. Vegetation is re-establishing itself on
the island with regrowth of tussock grasses and
Macquarie Island cabbage particularly noticeable
in places. Many seedlings have sprouted and
some of the smaller plant species are more
numerous than prior to the aerial baiting.
There have been no confirmed sightings of rats
and mice since the last bait drop in July 2011.
Out of an estimated pre-eradication population
of over 100 000, only 13 live rabbits have been
found during the ground hunting phase, with no
confirmed signs of rabbits since December 2011.
A two year monitoring period includes intensive
searching for any surviving rabbits.
There may not be signs of rabbits or
rodents on the island, but there is ever
growing evidence of ecosystem recovery.
environment.gov.au
Images (L–R): Macquarie
Shield ferns.
Island
(Photo:
on a
Stephen
misty day.
Horn),
(Photo:
Petrels
Richard
nesting
Dakin),
at Gadget
RoyalGully.
penguins.
(Photo:
(Photo:
ChrisGreg
Howard).
Stone).
In March 2013 long term vegetation monitoring plots
were revisited for the first time. Rapid recovery was
noted in some of the most palatable and visible
species, such as the megaherbs Stilbocarpa
(Macquarie cabbage), Pleurophyllum hookeri
(silver-leaf daisy) and Poa foliosa (tussock grass).
The shield fern, Polystichum vestitum, is showing
good recovery in the exclosures built six years ago
to conserve a ‘seed’ population. Small populations of
the shield fern are also starting to appear in scattered
locations across the island. The introduced species
Poa annua (meadow grass) forms thick lawns in
places. Epilobium brunnescens (a low-growing,
mat-forming herb) also appears to be more common
than previously recorded. Moss cover is higher at all
sites in 2013 than in previous years.
The most unexpected and exciting find on the
island was the rediscovery of the small herb
Galium antarcticum (subantarctic bedstraw) on the
northern shore of Skua Lake. The species was only
known on Macquarie Island from a single collection
at Skua Lake in 1983. Searches by botanists over
following years had failed to relocate the species.
The species has recently been listed as critically
endangered under Australia’s national environmental
law, reflecting its extreme rarity in Australia.
Galium antarcticum. (Photo: Nick Fitzgerald)
Shield ferns. (Photo: Stephen Horn)
It is not only the vegetation that is recovering.
Blue petrels are now breeding in more widespread
nests on the island, whereas in the past rat
incursions restricted their breeding to offshore
stacks. Terns have been seen breeding on
cobblestone beaches and grey petrels have
had their most successful breeding season since
recording of their populations commenced in 2000.
The intervention and action to eliminate
rabbits, rats and mice on Macquarie Island
is leading to a resurgence of this unique
landscape’s spectacular natural beauty
and recovery of its outstanding World
Heritage values.
Petrels nesting at Gadget Gully. (Photo: Chris Howard)
environment.gov.au
Images (L–R): Macquarie
Shield ferns.
Island
(Photo:
on a
Stephen
misty day.
Horn),
(Photo:
Petrels
Richard
nesting
Dakin),
at Gadget
RoyalGully.
penguins.
(Photo:
(Photo:
ChrisGreg
Howard).
Stone).