For many ecologists associated with the islands, the solution to the matter seems clear: poison the rodents.
"Nobody is happy about maybe having to use poison," Pyle says. "Nobody wants to do it, but when you weigh the costs against the benefits, it's probably worth doing."
The idea is more than an informal conversation topic. In October, the federal Fish and Wildlife Service released a 700-page environmental impact statement discussing the Farallones' mice and dozens of ways to potentially address the matter. Doug Cordell, a spokesman with the service, says his agency considered a total of 49 different solutions to the infestation, including releasing cats onto the islands, using traps to curb their numbers and checking their fertility using medicine-laced bait. Most of these proposed actions have been dismissed, he says, leaving on the table just three. Two involve poisoning the rodents. The other would be to do nothing at all.
"We wouldn't move forward with any option that posed more risk to the environment than benefits," Cordell says. "Our job as an agency is to serve and protect wild lands and wildlife."
Cordell stresses that the Fish and Wildlife Service currently has "no preferred alternative."
Yet he describes the mice at the islands as "plague-like" in numbers, and he tells the Bohemian that successful rodent eradication would require removing every single individual mouse from a population. Traps, he says, would likely fail to substantially dent the mice's numbers. Cats, too, would not catch every last one, and would certainly prey on the Farallones' birds.
It may sound like an unlikely prospect—eradicating invasive rodents from a place where the ground appears to crawl with them. Yet this has been successfully achieved on many small islands worldwide. For instance, Anacapa Island, off of Santa Barbara, was successfully cleared of rats in 2001 using grain-based pellets laced with a powerful rodenticide called brodifacoum.
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Jim Tietz/Point Blue
STUART Burrow owls have flocked to the islands for the mice, but are also eating rare native birds in the winter and spring.
This is likely the poison that would be used at the Farallones. A tiny amount would be applied, according to Cordell. He says the pellets under consideration contain just 0.005 percent rodenticide—such a low density, Cordell says, that any bait pellets that drift into the ocean would dissolve and be rendered virtually harmless.
The pellets would not be aimlessly scattered either, according to Jaime Jahncke, a researcher with Point Blue Conservation Science, formerly the Point Reyes Bird Observatory. Jahncke, who backs the poisoning plan, says the pellets would be dropped from a low-flying helicopter and directed away from the tidal zone via a deflector at the mouth of the dispenser. This, he says, would minimize the number of pellets that reach the water.
Even if some pellets do dissolve into the tide pools, it may be unlikely that the marine environment would be effected. Jahncke points to an accidental spill in New Zealand in 2001 that put 15,000 pounds of poison pellets—containing almost a pound of brodifacoum—into a tidal marsh. The event, he says, had virtually no lingering measurable effects. Harvesting of shellfish for consumption was temporarily banned after the accident but was soon green-lighted again by officials.
"And that case involved a closed waterway and a humungous amount of poison placed directly into the water," says Jahncke, who is also a member of the five-person Gulf of the Farallones National Marine Sanctuary Advisory Council.
By comparison, the proposed poison drop at the Farallones would involve no more than about two tons of pellets containing 1.5 ounces of brodifacoum. If officials opt for another rodenticide called diphacinone—less potent than brodifacoum—they will use about 16,000 pounds of pellets containing up to about a pound of the poison.
Still, opposition to the effort is strong. Jared Huffman has made statements questioning the wisdom of the plan, and the Marin County pest-management company WildCare Solutions is a firm opponent. The general public seems also to be leaning against the idea. Hundreds of written objections to the poisoning plan have been submitted to the Fish and Wildlife Service through its website since August.