Two adult rats have been caught and killed on Lord Howe Island, marking the first time rodents were seen there since a $16m eradication program began in 2019.
The rats were spotted by a local woman, who reported a sighting on a road near Ned’s Beach Cemetery last Wednesday, before an effort was mounted to catch and kill the animals.
Both had been killed by Friday and an autopsy revealed the pair to be a male and a pregnant female.
Atticus Fleming, the chair of the Lord Howe Island board, said no other activity had been detected as of Monday morning but investigations were continuing.
“The preliminary view is that the rats were likely an incursion from the mainland, such as by cargo, rather than the survivors of the initial eradication,” Fleming said. “Genetic testing will investigate the issue.”
As a precaution, a “strategic response strategy” has begun, involving rat detection dogs, the placement of monitoring and baiting stations, and “targeted inspections of high facilities”.
The last rat seen on the remote island 700km north-east of Sydney was flushed out by a detection dog in 2019 as part of a sometimes controversial program to rid the island of its rodent population.
It was a vast effort that involved 22,000 lockable traps being placed around the island and pellets of rat poison being dropped by helicopter in inaccessible areas.
At the start of the program in 2019 Lord Howe Island had an estimated rodent population of 300,000 rats and mice – roughly 1,000 rodents for each of the island’s 350 residents.
The animals were said to have arrived after jumping ship. Mice first appeared on the island in 1850, with rats following in 1918 after escaping from a ship that sank off the coast.
They were responsible for driving several native species extinct, including five land birds, 13 invertebrates and two plant species.
Next on the list was the dwindling population of the flightless Lord Howe woodhen.
After concerns were raised that the birds may eat the rat poison pellets, they were moved to an isolation pen managed by Sydney’s Taronga zoo while the program took place.
Since having been returned to the island’s environment, woodhen numbers have rapidly recovered – from 250 birds to 460 in February.
While some locals have reported rodent sightings in the past, the discovery of the rats on the island represents a new phase in the program to keep the rats out.
This involves strict biosecurity arrangements to keep the risk of new rodents arriving by boat or plane “as close to zero as possible”.
“A rapid response to detect and deal with any incursions, such as is happening now, is part of the ongoing program to help keep the island rodent free,” Fleming said.
This story was corrected on 19 April to clarify the woodhens were moved to an isolation pen on Lord Howe Island not mainland NSW.