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An island in Hawaii has declared itself free of invasive rats that were blamed for eating local seabirds and destroying native plants.
The rodents had plagued Lehua Island for decades and proved difficult to tackle, with a failed attempt to eradicate the population taking place in 2009.
Using bait and traps over a two-year period, Hawaii’s Department of Land and Natural Resources (DLNR) said it had now successfully managed to rid the island of the last of the introduced rats.
“After extensive on-island monitoring, we’re 99.99 percent certain there are no more rats on Lehua, which builds on the successful removal of invasive herbivorous rabbits, and secures a future for Hawai’i’s wildlife and ecosystems,” said Sheri S. Mann, the Kaua’i branch manager for the DLNR Division of Forestry and Wildlife. Rabbits were eradicated in 2006.
“This great work ensures that Hawaii’s Seabird Sanctuary can once again safely host our native seabirds that are so crucial to the ecosystem and our local fisheries,” said Mele Khalsa, of the non-profit Island Conservation, who served as the technical adviser on the eradication program.
“The operation went really well, and almost immediately we saw signs of recovery across the island. But in the months that followed, cameras captured an unexpected outcome, a small number of rats were still present on the island.”
Officials then launched a “mop-up effort” to remove the last few individuals, including using motion-sensor cameras to detect where rats were present.
Khalsa added: “Lehua is a story of what we can achieve through dedicated and focused conservation efforts, and securing the island has been a critical stepping stone for the protection of Hawaii’s native birds and plants.”
Dr. Patty Baiao of Island Conservation said: “We have collected robust data on the rat activity on Lehua since the eradication operation in 2017.
“With the success of the mop-up effort, rats have not been detected on the island for over two years. April 2021 marks the one-year anniversary since all rat-control treatments were removed from the island, adding to the data that allows us to declare Lehua rat-free.”
Lehua is home to at least 17 seabird species, some of which are threatened. Hundreds of thousands of birds base themselves on the island during the summer nesting season.
Conservationists hope the endangered Newell’s Shearwater, which had previously been found trying to nest on the island but was unsuccessful due to the rats, might now thrive on Lehua.
They also plan to restore 14 native plants, 11 of which are found only in Hawaii.
“There’s no doubt that the rabbits initially, but the rats in the long-term, caused a lot of plants to disappear,” said Mike DeMotta, a botanist with the National Tropical Botanical Garden.
“Restoring the ecosystem generally will not only be a benefit to the birds, but also any other organisms that are native there. There are probably dozens of undescribed Hawaiian micro-moths and other things that are occurring that will really benefit from ecosystem restoration.”
It is also hoped that the seas surrounding the island will be boosted by rat eradication.
Seabird excrement, or guano, is a highly effective fertilizer that can improve the health and diversity of corals and fish—including local manta rays.