Rodents on Lord Howe Island
“Rats have been the single most destructive animal on Lord Howe Island.”
The worst feral mammal to arrive on Lord Howe Island was the Black rat, Rattus rattus. They first arrived on the island in 1918 from the cargo ship Makambo and quickly multiplied, wreaking havoc with the wildlife. Within ten years of arriving the rats had eaten five landbirds into extinction. More recently, two plant species and a number of invertebrates have disappeared.
The Rat Eradication Programme (REP)
In 2002 the Lord Howe Island Board began to investigate the feasibility of removing rodents from the island. Over the next seven years a draft plan was prepared to carry out a rodent eradication, based on experience and research from around the world, especially New Zealand, where the process was pioneered in 1980.
Funding for the Lord Howe Island project was received from State and Federal governments in 2012, and fine tuning of the program was carried out.
2019 was the culmination of this work, when a multidisciplinary team including world experts, local scientists, and other Australian workers assembled to carry out the rodent removal operation.
Basically, the plan was to deliver a poison bait pellet to every rat and every mouse on the Island – possibly up to 120,000 of each.
Bait stations were put out across the settlement in April 2019, by a ground crew of 50, placing the stations every 10 metres on the ground (about 19,000 bait stations). These were placed very accurately using GPS units to an accuracy of about 10 cm. Smaller bait stations for mice were installed inside all buildings on the island.
The next task was to catch 230 Woodhens and 120 Currawongs, to isolate them from the poison. Staff from National Parks and Wildlife and the LHI Board collected birds from across the Island, including the summit of Mounts Lidgbird and Gower, and on Big Slope. Helicopters were used to ferry the catchers into these remote spots and then ferry the Woodhens down to the airfield for transport to the facilities being run by Taronga Zoo staff. The first point for birds as they were handed over to Zoo staff was the research station where Taronga Zoo’s chief vet and nurses gave every bird a thorough health check. The birds were placed in cages specially designed by Zoo staff for holding these two species. Currawongs were placed in their pairs in individual cages. Woodhens were placed in larger enclosures housing 20 birds, because it had been determined with Wekas in New Zealand as an ideal way to hold rails in captivity for long periods, as they lose their territorial aggression in such a situation. The Taronga Zoo nutritionist had worked on a special diet for each species.
With the birds secure, the bait stations were filled and checked weekly from May to October 2019. In some of the paddock areas adjacent to the mountain and forest areas, staff hand broadcast baits, walking lines on a ten-metre grid. For some cattle owners who wanted to retain cattle on the Island, wooden rooves were placed over each bait station in those paddocks.
After the lowland areas were baited, it was time to wait for windows of good weather to fly in by helicopter and distribute baits in the areas away from the settlement. This was tricky as the weather windows were quite tight – wind less than 15 knots, no low cloud and with a forecast for the following three days to allow less than 5 mm of rain.
In addition to the weather, another compounding factor was the presence of Providence petrels around the southern mountains. These birds fly out to sea before dawn, but begin to return around midday. Spotters were stationed in the mountains to observe Providence petrel numbers returning and alert the operations manager to significant numbers present that may pose a hazard to the helicopters.
The windows for the flights came, and two bait drops were carried out, one in June and again in July. There was great relief with the accomplishment of this, as weather in winter can be windy and wet.
Ground baiting had to continue, with weekly checks of bait stations ongoing until the end of October. At a number of bait stations there were indicators put out to attract rodents and record activity (wax blocks with peanut butter).
When any signs of rodents, or reports of them by residents, were observed then the Board dog-handlers came around with the dogs trained to detect rodents. Slowly the number of sightings and signs decreased, and no live rodents were detected after September 23rd 2019.
Release of Currawongs and Woodhens
The captive Currawongs were released in September 2019; the Woodhens were released in January 2020. Both of these species were observed breeding almost immediately, and have been doing well. In conjunction with the rodent eradication there has been an eradication program for introduced Masked owls.
A program using detection devices and sniffer dogs continued to mid-December, with no signs of live rodents detected from the end of September 2019.
Visible benefits of the REP
The benefits from the rodent eradication are being monitored and significant increases in birds, invertebrates and plants species are being recorded. A survey of the Woodhens in November 2020 counted 434 and then 640 were recorded in March 2021. Residents reported increases in Emerald doves and other land birds. Seabirds also appear to be increasing the range where they breed.
Increased biosecurity measures were put in place to minimise the chances that rodents return via shipping or aircraft. This involved rodent monitoring stations across the settlement, and sniffer dogs to check freight going on and coming off the cargo ship, and arriving via aircraft.
A re-incursion in 2021
In April 2021 a Lord Howe Island resident observed two rodents on the road near Neds Beach. Increased monitoring and surveillance by dogs commenced and further rats were located and dispatched.
The Lord Howe Island Board and NSW government acted quickly and put a lot of resources and personnel into addressing this incursion. Some of the New Zealand experts on rodent eradication were brought in to lead the program. Bait stations, bait monitoring devices, night time cameras and sniffer dogs were used to catch the rats.
By July 2021, 78 rats had been caught. Biosecurity measures were increased to ensure no further incursions occur. Hopefully this re-incursion has been checked, but the situation is still being strictly monitored.