Is mass poisoning the only way to solve the Farallon Islands’ overwhelming rodent problem?

There are so many mice on the Farallon Islands that sometimes the ground appears to be undulating, a gently rolling tide of rodents.

The mice do not belong on the Farallones, an archipelago 27 miles off the coast of San Francisco. They are tiny interlopers, descended from the escapees off seal-hunting ships in the 1800s. Since then, they have proliferated. There are tens of thousands of them, converging on what scientists say is one of the highest densities of rodents anywhere in the world.

They eat insects, depriving native salamanders of their diet. Owls come to the islands to eat the mice, and then start preying on the Ashy storm petrel, half of whose global population of 8,000 lives in the Farallones. They’re spreading invasive plants on their fur, too.

In short, they are destroying the unique ecosystem, and the U.S. Fish and Wildlife Service is now the subject of national headlines for its plan to, in turn, destroy the mice.

The plan is to dump 1.5 tons of rodenticide, which should be enough to kill every last mouse on the islands. Of course, there was a lot of concern around the plan — even Fish and Wildlife admitted some seabirds would likely die as part of the initiative. Because of the intense pushback, the plan was put on hold on Wednesday.

MOREFederal officials withdraw plan to drop poison on Farallon Islands

California Coastal Commission spokeswoman Noaki Schwartz said the plan would be reworked and resubmitted once concerns had been addressed.

“The only way to protect these species and allow the ecosystem to recover is 100 percent eradication of the mice,” Pete Warzibok, a biologist who has worked on the Farallon Islands for more than 20 years, told the Associated Press. “Anything else is simply a stopgap measure that will not adequately address the problem.”

According to the U.S. Fish and Wildlife Service, mass poisoning is the only viable proposal to permanently cull the rodent population. Why not introduce a ton of cats, you may be asking. Or trapping and relocating the mice?

Fish and Wildlife went over dozens of different scenarios and shot all of them, save rodenticide, down. To find out why Fish and Wildlife believes other alternatives won’t work, check out the gallery above.

Katie Dowd is the SFGATE Senior Manager. Email: katie.dowd@sfgate.com | Twitter: @katiedowd

This post was originally posted at https://www.sfgate.com/bayarea/article/san-francisco-farallons-mice-rats-infestation-14086006.php.

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