Controversial plan to airdrop poison onto the Farallon Islands to eradicate mice gets green light - SF Gate

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The Farallon Islands have a problem.

The rocky outcrop of sea stacks and islands 30 miles west of the Golden Gate are overrun with invasive house mice, and the Biden administration is doubling down on a solution from the skies.

In an attempt to eradicate the rodents, a controversial plan to air drop 2,900 pounds of poison-laced bait from planes is going ahead.

The islands are home to 300,000 breeding seabirds, as well as five species of seals and sea lions. It's also the only place in the world for a unique insect: the elusive Farallon cave cricket.

The rich biodiversity, however, also includes more than 1,000 mice per acre.

First introduced by sailors in the late 19th century, the Farallon Islands’ mouse population has exploded in recent years. The rodents choose to eat native plant species over invasive species, spreading the seeds. They also consume salamanders and salamander eggs.

The mice have thrown the island ecosystem off balance, according to the Point Blue Conservation Science research institute, and attract burrowing owls throughout the year. When the mice population drops during the winter, the owls turn to another food source for sustenance, the ashy storm petrel. Research models found that if the mice, and therefore owls, were to remain, the ashy storm petrel population could decline by 63%, reports the Marin Independent Journal.

“You can see the grass move with the mice,” Fish and Wildlife spokesman Doug Cordell told KPIX in 2019. “That’s how many there are out there. So it’s plague-like infestation.”

“They’re just covering the ground,” Pete Warzybok, Farallon Islands program leader for Point Blue told the Marin Independent Journal. “During this time period, the island is riddled with mouse burrows. There are times when you walk outside and you actually see the ground undulating as the mice are running about below the surface. Quite frankly, it’s a horrifying sight. It’s like something right out of a horror movie.”

The poison-from-above solution has been years in the making, but not welcomed by all. Concerns were raised in 2019 that the rodenticide to be dropped on the islands has a 120-day life span and could pollute soils, waters and wildlife. But after other fixes, such as using contraceptives, individual traps and pathogens were ruled out, the plan was given the green light by the U.S. Fish and Wildlife Service this week.

The agency plans on dropping the poisoned bait in the late fall and early winter, when bird numbers are lowest.