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At last: Lord Howe Island rodent eradication program approved


 
Play  At last a start date for rodent eradication on Lord Howe Island  wsnclhi3oct2017.mp3  
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Nicholas Carlile, a Principal Scientist at the NSW Office of Environment and Heritage, charts how rodents will finally be removed from the Australia’s offshore Lord Howe Island.
Lord Howe Island, volcanic in origin and 6 million years old, is about 500km off the coast of Port Macquarie in the Tasman Sea. It is on route to Norfolk Island, discovered by James Cook, but wasn’t discovered until those establishing the penal colony in Sydney Cove sailed directly to Norfolk island to create a farming island to feed Sydney Cove.  Therefore the first people ever to  arrive on Lord Howe were in May 1788 where they filled their ships with turtles and birds and fresh water while on their return to Sydney Cove.


 

The island was descibed as like paradise; it had no rodents or other mammals and was a haven for birdlife and also many unique invertebrate species and flora. Currawong are  top predators - even  described as the lion of Lord Howe.
Left: This subspecies of Pied Currawong lives only on Lord Howe Island where it is the top daytime predator and helps preserve the ecological balance Click here for soundfile. 
Inevitably, humans brought rats and mice who soon descimated the island's ecological balance. The first rodents known to arrive were house mice, probably in food stuffs being transferred between Norfolk and Lord Howe  in 1869.


 

The real terror, Rattus rattus (the ship rat), arrived through the careening of a vessel, The SS Makambo, that had hit rocks on the Admiralty Islands north east of Lord Howe. The Makambo was run ashore at Ned’s Beach and the stores it was transferring from Sydney were all offloaded. Unfortunately that also included Ship rats, with stories saying the origin was a rat’s nest in the back of an offloaded piano.


 
Being subtropical the conditions on Lord Howe were quite benign and rats had taken over the island within 2-3 years. Since establishing themselves the rats have destroyed the native Lord Howe phasmid (still found on Ball’s Pyramid) and five species of bush birds. They have also adversely impacted seabirds some of which only bred on the outer islands where there were no rats.
Left: Nicholas Carlile holding the rarest insect known - the Lord Howe Island Phasmid (image by Patrick Honan) Click here for story and soundfile.

 
Lord Howe had tried to establish a number of industries over the years, looking for an income from things they could sell back to the mainland. It had a particularly difficult time with industries over those years until tourism kicked off in the 1930s. It had onions in the 1860s until they got blight, then lemons and other crops until disease wiped them out. Finally they established a palm industry, selling the native kentia palms to Europe, but the rats ate the palm seeds as well as chewing out the stipes, the stems of the leaves. The palm industry really suffered so rat control was introduced from the 1950s with systematic baiting from the 1980s. Originally there was a bounty on rats’ tails and owls were introduced a number of times, including a hybrid version of the masked owl. Still the rats persisted and islanders spent large amounts of money ensuring rats weren’t around lodges and settlements. Tourists couldn’t have outdoor buffet dining at night because of the rats! 

 

Recent studies  found that Little Shearwaters were losing a third of their chicks to rats and Black-wing Petrels, which go into torpor when on their nests, were having their eggs taken out from under them! In 2001-2 it was decided that it was beholden on NSW National Parks and Wildlife (now Heritage) to come up with a decent plan for rodent eradication of rodents, now the only feral pest left after removal of goats, pigs and finally cats.


 
Above: Ship rat removing a Black-winged petrel egg from an unbaited area on Lord Howe’s North Head (image from OEH).
Below: Ship rat removing a half grown Black-winged petrel chick from a nest at Blinkys Beach on Lord Howe.  Despite regular baiting in this area to control rodents, less than 10% of nests were able to raise young in 2016/17 (image from OEH).

 

It is easy to eradicate rats on a level island but a 1400 km² island with two large mountains and 600m cliff drops is not as easy as a flat one.
In addition, the rodent eradication plan could not disrupt tourism or impact humans or human health. Lord Howe has 350 permanent residents living there as well as 20-25,000 visitors each year and the island’s economy is almost solely reliant on tourism. 


 

It uses an anticoagulant in the baits so the rodents haemorrhaged internally and bled to death. Because rats are clever and would otherwise just avoid the baits if the effects were immediate, the poison takes about six days to have any effect. Once it does, however, the rats die within 24 hours. Laboratory baiting studies were carried out on Lord Howe in 2013 and 2016 to determine the levels of the poison required to ensure the baits actually killed the rodents.


 
Below: Trial baiting in 2007 with a non-toxic bait containing a glowing marker showed that most native birds and the native bat would not consume the type of bait planned for the eradication (image from OEH).

 

Earlier studies, using non-toxic bait examined the potential effects of bait on other wildlife. The poison is non-soluble (so can’t dissolve in waterways and affect fish or eels), doesn’t impact invertebrates and is less toxic to birds. The Lord Howe woodhens were attracted to the baits and will be removed to safety before any eradication begins. The Lord Howe Currawong has the potential to eat dead or dying rodents so much of its population will be in captivity during the early baitings.


 

The Lord Howe Island Board agreed last September to allow the eradication since all state and federal licences have been approved and everyone has agreed that best practice would be maintained. The program will start on the 1st June 2018 (weather permitting) and by months end there should be no rodents. 100 tons of rubbish has already been removed from the island and the ground baiting and hand baiting will cover all settlement areas, including every shed, roof cavity and sub-floor. The baiting is deliberately planned for winter when food resources are quite poor. 

Below: The lowlands of Lord Howe are dominated by housing and agriculture with settled areas being hand-baited for the eradication of rodents. The remainder of the island will have bait spread by helicopter. 


 
While the eradication itself will take days (with a follow-up some 14- 21 days later), it will take two years of monitoring to prove the $9 million eradication a success. Two security dogs will sniff out any rodents left on the island as well as sniffing all shipments that come in by sea or air. The dogs are also trained to sniff out big-headed ants and myrtle rust, a recent problem. It is all a huge task that has taken many years of planning and testing but it is how rodents will be finally eradicated from Lord Howe Island.

 
Nicholas Carlile was interviewed for A Question of Balance by Ruby Vincent. Images from Nicholas Carlile. Summary text by Victor Barry, October 2017.

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