Lord Howe Island moves closer to rat
- The Aussies intend going where
others fear to tread
Edited by Judy Gilbert and
Like New Zealand and other geographically isolated islands of the
pacific, many of Lord Howe Island’s endemic species of birds, reptiles
and invertebrates has been decimated by the aggressive and highly
competitive European mouse and the black (ship) rat. Like Great Barrier
Island, Lord Howe is inhabited by people, visited by tourists and has
farmed animals and domestic pets. The Aussies however are intending to
boldly go where others have yet to tread – they intend to eradicate mice
and rats from Lord Howe.
Planning for the eradication of rodents
from Lord Howe Island has progressed with financial support from the
Australian Governments Natural Heritage Trust, the NSW government, the
Foundation for National Parks and Wildlife, and the Lord Howe Island
Board. Recently the Board has received all the funding to implement its
proposed rat and mice eradication programme.
The Lord Howe Island group is 760km
north-east of Sydney and the group consists of Lord Howe Is (1455ha),
Roach Is (15ha), Mutton Bird Is ( 4.5ha) and Blackburn is (3 ha) plus
smaller rocks and islets. Great Barrier, by comparison, is 28,000 ha
including all its outlying islands, islets, and rock stacks. The
resident population on Lord Howe is around 350 in approximately 150
The outstanding natural beauty, together
with its diverse flora and fauna, was recognised in 1982 when the island
group was made a World Heritage Site. Tourism is one of two major
sources of income with about 16,000 visitors each year (Great Barrier is
estimated to have about 28,000 visitors a year.) Visitor numbers on Lord
Howe are regulated to a maximum of 400 on island at any one time. The
growth and export of kentia palms provide the other main source of
income for the islanders with the Lord Howe Board operating a nursery
that exports 2-3 million palm seedlings annually.
The first mice reached the islands in the
1860s followed by ship rats in 1918. Within two years the rats were so
widespread that a bounty system was implemented to try and control them.
The environmental effects were noticed immediately with one local
commenting in 1921 “one can scarcely imagine a greater calamity in the
bird world than this tragedy which has overtaken the avifauna of Lord
Rats are implicated as the “key
threatening process” in the extinction of five species of endemic birds,
two species of plants, and at least 13 species of invertebrates with
another 13 species of birds, two species of reptiles, 51 species of
plants, and numerous invertebrates now threatened.
* Kentia palm seeds are prime
rat diet on
Lord Howe Island.
The Lord Howe Island (LHI) Board embarked
on eradication planning in 2006 following a study in 2001 which
concluded that the eradication of rats and mice was technically
feasible. A cost benefit study in 2003 demonstrated that costs of the
eradication would be quickly offset by discontinuation of the current
rat control programme and increased yields of commercial palm seed. If
undertaken, Lord Howe and its smaller islands would be the largest,
permanently inhabited island, on which the eradication of ship rats and
mice has been attempted.
Control or Eradication
There have been attempts to control rats
on LHI since about 1920. Currently control includes protection of the
kentia palm over about 10% of the island using about 1000 bait stations
replenished 5 times a year with anticoagulant baits. Brodifacoum is used
around the island’s commercial palm nursery and by residents in and
around residences. This control effort currently costs the LHI Board
about A$65,000 per year.
* The topography of Lord Howe contains
rugged bush clad peaks
as well as lowland pasture -very similar to Great Barrier Island.
The increasing frequency and success of
island eradication programs and the increasing costs and limited success
of control on LHI led the Board to examine the feasibility of
eradicating ship rats and mice from the islands.
In 2003 the LHI Board reviewed the risks
and constraints around eradication and assessed the various costs and
benefits involved. This report demonstrated the financial benefits if
rats were eradicated and also acknowledged the biodiversity benefits. An
eradication would thus provide overall benefits greater than can be
achieved through the current control programme.
A draft plan for the eradication was
developed in 2009 in consultation with expert planners and practitioners
from around the globe together with the LHI community.
The challenges include: (1) the
complexities of targeting two pest species; (2) the existence of
threatened endemic species that are susceptible to poison; and (3) the
presence of a resident human population, a well developed tourist
industry, domestic animals and livestock.
The plan recognises that:
• Eradication rather than ongoing control is the most effective
• The impacts of rodents on LHI are significant and ongoing;
• Eradication is feasible using current techniques without unacceptable
risks to non-target species and humans.
The operation will utilise the cereal
based Pest-Off Rodent Bait containing Brodifacoum at the concentration
of 20ppm. The primary method of bait application will be through 2
aerial broadcasts 10-14 days apart, with hand broadcasting or bait
stations used in areas not suitable for aerial application, such as in
the settlement area or where livestock are present.
Mitigating Potential Impacts on Threatened Species
Brodifacoum has been used effectively to
eradicate rodents on islands and in fenced sanctuaries worldwide more
than 200 times. It does however, affect some non target species and for
LHI an evaluation of the potential risk to these species has been
carried out and been given prime consideration.
* Lord Howe's iconic woodhen - focus of
the mitigation effort.
Birds – There are four endemic species
that survive on LHI: the LHI woodhen, the LHI pied currawong, the LHI
golden whistler and the LHI silvereye. Since 2007 the numbers and
habitat of these species has been carefully monitored. From trials using
non-toxic baits it is known that the woodhen (similar to our weka) and
the currawongs would be at risk of taking bait or secondary poisoning
from eating poisoned rats. To minimize the potential impact at least 85%
of the woodhen and 50% of the currawong population will be placed in
captivity for the duration of the risk.
Captive management will require the
construction of a precision built, rat-proof enclosure for woodhen and
aviaries for other species. The surrounding areas will be baited before
and after the main eradication to ensure they do not harbor any rats.
Reptiles and Mammals – Two species of
native reptiles are present on Lord Howe and its nearest neighbour
Norfolk Island: LHI skink and LHI gecko. The insectivorous diet of the
species exposes them to the risk of ingesting Brodifacoum if they feed
on invertebrates that have ingested the bait. However, the risk of
secondary poisoning is low because of the different blood chemistry of
these reptiles and because the baiting will take place in the winter
when reptiles are less active. There have also been no wide-spread
deaths of reptile species following rodent eradications. In many
instances the removal of rodents has resulted in a substantial increase
in the abundance of reptiles. For example the number of skinks on
Korapuki Island increased 30-fold within five years of rats being
The only extant native mammal on LHI is
the large forest bat, a species that is common throughout much of
southern Australia. It is insectivorous and is therefore considered to
be at low risk of poisoning.
Invertebrates – The LHI group has numerous
endemic species of terrestrial invertebrates and predation by rats is
regarded as a significant threat to many. Only one species is considered
to be at low risk from bait, the Lord Howe flax snail, so a number of
snails will be collected and housed in captivity for the duration of the
Effects of Human Habitation on Eradication Design
A human population and their associated
pets and livestock raise issues rarely encountered on other large
islands where eradications have occurred. However, modifications made to
ensure the safety of the community need not jeopardise the success of
Currently there are 100 beef cattle and a
herd of 14 cows provides milk for local consumption. There are also 3
horses, 12 goats, and 300 chickens on the island. Pigs are prohibited.
Beef cattle will be destocked through slaughter during the two years
leading up to the eradication. Owners will either be compensated
financially or given replacement stock brought to the island when the
breakdown of bait is complete. Most owners of stock have indicated their
willingness to cooperate in this process. The dairy herd as well as
goats and horses will remain on island throughout the operation, with
animals confined to a small paddock connected to the existing milking
shed by a narrow race. Confinement will extend until baits disintegrate.
Cattle proof bait stations will be placed within the 30 m buffer zone of
All poultry will be eliminated from the
island at least a month before the eradication and be replaced after the
eradication. Poultry owners will be compensated for lost egg production.
There are approximately 48 domestic dogs
on LHI. Cats are prohibited. The option of removing dogs to kennels on
the mainland will be available for all dog owners at no cost. Given the
current high use of poisons in the settlement are now, most dog owners
are aware of the risks to dogs, nevertheless an education programme will
be implemented to advise island residents of the potential risks to pet
dogs and how to avoid them. Any cases of poisoning will be treated
Community baiting strategies The proposed operation on LHI will utilise
a combination of aerial, and broadcast, and bait station techniques in
order to deal with issues associated with human habitation, public
concern about aerial baiting in a residential area, and to protect
potable water storages. Each property will have a negotiated ‘property
action plan’ with agreements with the LHI Board about effective and safe
actions on each property. These plans will detail: how and where the
bait will be distributed on each property; methods to control rodents in
the lead up to the eradication; management of pets; procedures to ensure
the health and safety of all family members; and procedures to dispose
of compost and food waste before and during the eradication.
* The black rat, a very successful
A biosecurity strategy current exists for
LHI. Additional measures needed to ensure that rodents are not
reintroduced once they have been eradicated include; improved checks of
cargo before departure from the mainland; in-transit checks of sea
freight; pre-landing inspections of the cargo vessel and private yachts;
arrival inspections of all aircraft and passengers using trained
Several community meetings and focus
groups have been held on LHI to inform the community about the need for
an eradication, how it would be undertaken, and when it is likely. The
meetings outlined environmental benefits of rodent eradication, along
with the potential flow-on effects for tourism. Explanations were made
of the operations’ best practice and how it drew on the wealth of
previous successful operations. The potential risks were identified and
the contingencies built into the planning process to ensure risks were
mitigated. What was also explained was the continued risk to children,
non-target species, livestock and pets with continued use of baits over
A survey on LHI in in 2009, approximately
15 months after the commencement of consultation, indicated that 96% of
the 126 respondents agreed with the need to eradicate the rats from the
island. Many concerns raised by the community can be addressed through
appropriate information. Topics include ; (1) impacts of rodents on
islands; (2) the benefits of rodent removal; (3) the impacts of baiting
on non-target species; (4) the choice of poison; (5) the methods of bait
dispersal; (6) human health risks; (7) risks to the marine environment.
Where is it up to now?
Currently the project managers are
preparing a brief to engage specialist consultants to:
(a) Provide strategic advice on the
approach to inform, consult and engage the community (and other relevant
individuals and groups) on the development and implementation of the
Rodent Eradication Plan.
(b) Assist with the establishment of a Community Liaison Group and
provide professional facilitation of the initial 3 meetings of the
(c) Provide Draft Communication/ Community Engagement Plan in
consultation with CLG for review by Steering Committee.
The GBI Trust is keeping in close
communication with the project as its complexities are similar to those
that would be experienced by Great Barrier if it were to undertake a
similar type of eradication.
If the eradication of rodents from this World Heritage Site can be
achieved it will arguably be one of the most significant management
actions undertaken for threatened species conservation in Australia and
provide a blueprint for other inhabited islands keen to restore their
*Extracted from the paper “Rodent
eradication on Lord Howe Island: challenges posed by people, livestock,
and threatened endemics” By I.S.Wilkinson and D. Priddel.