Should poison be dropped on a mouse-infested island? California weighs plan

Ťhe Farallon Islands are home to squawking seabirds, floppy harbor seals, brightly-freckled arboreal salamanders and rare, delicate camel crickets. They are also home to what ecologists have called a “plague-level infestation” of European house mice.

星期四, the California Coastal Commission will vote on a proposal to eradicate the invasive rodents from the islands, located just off the San Francisco coast, by dropping 3,000lb of poisoned bait from helicopters. If the contentious plan moves forward and earns approval from the regional director of the US Fish and Wildlife Service (FWS), it could be implemented starting in the autumn of 2023.

The vote marks the culmination of years-long debate over how to address the Farallones mouse infestation. Officials from the FWS have been developing a plan to use rodenticide since the early 2000s, saying that the mice – whose population can reach up to 60,000 in the fall – are a threat to endemic species of birds, insects and reptiles.

The agency described the strategic use of rat poison as the only feasible solution to fully exterminate the mice, which breed and reproduce quickly.

But critics say that sprinkling rodenticide – which is also toxic to birds and other animals – is too risky. They’re skeptical that “nuking the island with a poison that kills everything” could end well, said Richard Charter, a senior fellow at the Ocean Foundation, who helped in the founding of the Gulf of the Farallones National Marine Sanctuary.

在 2019, FWS put forward and then withdrew a proposal to use the rodenticide brodifacoum after the coastal commission requested more detailed information on how officials would protect birds and other species.

The latest proposal says FWS staff would begin by “hazing” gulls to ward them away from the islands before the rodenticide is deployed, using techniques including “lasers, spotlights, pyrotechnics, bionics, predator calls, air cannons, effigies, and kites”. Burrowing owls and other raptors – who might eat poisoned mice and themselves get poisoned – would be gathered up and transported off the island. The proposal asserts that although the risks to endemic Farrallon arboreal salamanders are low, as a measure to safeguard the species, officials would also collect about 40 individuals and hold them in terrariums until the risk of exposure to the rodenticide has disappeared.

After helicopters rained brodifacoum-laced pellets on the islands, wildlife officials would walk around collecting mouse carcasses and uneaten pellets, so that other animals don’t ingest them. After a few months, the brodifacoum would also break down on its own, according to the proposal.

Wildlife officials and ecologists conducting research on the island say they need to act quickly to address the infestation. The mouse population, which was inadvertently introduced by sailors in the 19th century, now peaks at about 500 mice per acre.

“At times, if you’re out in the evening, you’ll see the ground moving as mice are digging their tunnels,” said Pete Warzybok, the Farallon Islands program leader at the non-profit Point Blue Conservation Science, which does biological research on the island. “It is a truly remarkable density of mice.”

Warzybok said that though the plan might seem drastic, similar strategies had worked on other rodent-infested islands. “The benefits of the project to the native wildlife will far outweigh any risks,“ 他说. There is evidence that mice directly prey on vulnerable endemic species including salamanders and crickets. They also affect plants and animals on the island in indirect ways. 一种 学习 from Point Blue found, 例如, that the mice draw in larger numbers of burrowing owls, which feed on them during the fall but then nosh on small seabirds like ashy storm petrels during the winter and spring.

Charter, 然而, was skeptical that such mitigation measures would do enough to protect wildlife and marine life. Even with precautions taken, the proposal includes caveats that some western gulls would be killed, he noted.

The use of brodifacoum is already restricted in 加利福尼亚, he pointed out, because it tends to travel up the food chain – killing not only rodents but also the raptors and mountain lions that eat them. He and other critics of the poison plan advocate for waiting until more humane alternatives – such as mouse contraceptives – are developed.

同时, 他说, wildlife officials could explore alternative means of protecting species such as storm petrels by looking holistically at the impacts of the climate crisis, light pollution and offshore oil drilling.

Brodifacoum, Charter said, “is the wrong chemical, and it’s being used in the wrong place”.