Mass rodent poisoning on this remote Australian island could bring back giant stick insect | Science

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Mass rodent poisoning on this remote Australian island could bring back giant stick insect | Science

Lord Howe Island has reefs, forests, and endemic species threatened by invasive rodents.

IAN HUTTON

A beguiling, 11-kilometer-long speck of land in the Pacific Ocean 780 kilometers northeast of Sydney, Australia, Lord Howe Island hosts some of the world’s southernmost tropical coral reefs as well as throngs of endemic birds and insects. But invasive species have laid siege to its unique biodiversity, the worst of them the black rats that first scurried ashore in 1918 after the steamship SS Makambo grounded on the reef. Now, a unique effort to eradicate the invaders is unfolding—against a background of controversy among the island’s roughly 380 human inhabitants.

To protect or restore native species, introduced rodents have been extirpated on more than 700 islands worldwide, many around New Zealand, with its rich but threatened endemic fauna. But the Lord Howe project, years in the making, “will be the largest rodent eradication undertaken on a permanently inhabited island anywhere in the world,” says Andrew Walsh of the Lord Howe Island Rodent Eradication Project, who is overseeing the effort to spread 42 tons of poisoned cereal pellets across the island. Some 28,000 bait stations were filled across farmed and residential areas starting 22 May, and helicopters will scatter baits over more forested and mountainous parts of the island as soon as weather permits.

Walsh and his colleagues hope to undo some of the damage from the voracious rodents, which have wiped out five endemic birds, two plants, and 13 insects, including the 15-centimeter-long, black, waxy-looking Lord Howe Island stick insect, also called the phasmid or tree lobster (Dryococelus australis). Some lost species, including the phasmid, have subsequently been rediscovered on surrounding islets. Eliminating the estimated 360,000 rodents—including house mice, which arrived in the 1860s—could allow the native animals to return to the main island, and will also protect another 70 or more threatened species, such as the little shearwater, masked booby, and several endemic palms that grow in the island’s cloud forest.

“It’s going to be a landmark project throughout the history of eradications,” says Ian Hutton, naturalist and curator of the Lord Howe Island Museum, who has led research and conservation on the island since the 1980s. But the fact that Lord Howe Island—a UNESCO World Heritage Site that is officially part of the Australian state of New South Wales—is a tourist destination with an established human population created a unique challenge. Many residents feared the baits might harm children, pets, cattle, and other wildlife or damage the lucrative tourist trade.

The island’s governing body decided in 2017 to go ahead with the AU$10.5 million eradication, after 15 years of research and planning and a referendum that saw 52% of islanders vote in favor. But others remained bitterly opposed. “This whole thing will be a disaster. We might as well kiss our World Heritage listing goodbye,” islander Rodney Thompson told Sydney’s The Daily Telegraph newspaper in April.

Rodents wiped out the cigar-size Lord Howe Island stick insect on the main island, but it clung to life on a nearby islet.

IAN HUTTON

“We have families that have been here six generations, and some have a sense of ownership of the island,” says Hutton, a longtime advocate for the eradication.

Originally scheduled for 2018, the effort was postponed for a year because of a snag in government pesticide permits, organizers say. The delay gave them time to rethink how baits would be distributed in occupied areas, which brought many remaining detractors on board.

People weren’t the only complication. Research in 2007 had revealed that the poison, a rodenticide called brodifacoum, might endanger two endemic birds, the Lord Howe Island woodhen and the Lord Howe Island currawong. Since April, a team from Sydney’s Taronga Zoo has been involved in rounding them up, housing the roughly 200 woodhens and 125 currawongs captured so far—more than half the wild populations—in aviaries and pens. The birds have “settled in beautifully,” says Leanne Elliott, wildlife conservation officer at the zoo. Once the poison has broken down, they’ll be released into the wild again, likely in stages toward the end of the year.

By then the rats should be gone, and biodiversity should start to rebound, says Melanie Massaro, an ornithologist at Charles Sturt University in Albury, Australia, who has been studying the currawong. Providing the eradication is successful, she says, “Some smaller seabirds that have been previously lost will likely start breeding on the island again; some populations of currently threatened species will increase in numbers, and there’s also the potential of reintroducing species.”

One early returnee might be the Lord Howe stick insect, long thought extinct. In 2001, a few individuals were found clinging to life atop windswept Ball’s Pyramid, a 551-meter-tall rocky sea stack 23 kilometers to the southwest. The insects have since been bred at Australia’s Melbourne Zoo, and in 2017 researchers confirmed that their DNA matches that of museum specimens collected from the main island more than a century ago. The first step in the species return will come in 2021 with a trial release of captive-bred phasmids onto an islet in Lord Howe’s lagoon that is now being revegetated.

“It’s all going to be done very carefully,” Hutton says. “In 100 years, there have been a lot of changes and the phasmid was part of an ecosystem that has altered,” he says, arguing that some of the missing birds may once have kept it in check. Without native predators, the stick insect population could surge.

Then again, some of those birds may return as well. Norfolk Island, about 900 kilometers to the north, hosts related subspecies of parrots, owls, and several other birds that once made their home on Lord Howe. They are contenders for reintroductions. Others, such as the Kermadec petrel and white-bellied storm petrel, found on surrounding islets, may return on their own—providing this summer’s campaign can end the centurylong reign of the rats.

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