Farallon Islands mouse poisoning plan divides conservation community

The California Coastal Commission will weigh in on the U.S. Fish & Wildlife Service plan at what’s expected to be a marathon meeting Dec. 16.|

Mouse Eradication Plan at the California Coastal Commission

California Coastal Commissioners are expected to hold a marathon hearing Thursday to determine if the U.S. Fish and Wildlife Service’s plan for poisoning invasive mice at the Farallon National Wildlife Refuge is consistent with policies in the California Coastal Act.

The virtual meeting begins at 9 a.m.

More information is available at coastal.ca.gov/meetings/agenda/#/2021/12.

Golden hills and colorful leaves may define autumn for much of Northern California, but on the South Farallon Islands it is the mice — tens of thousands of them.

Since they arrived on the island refuge west of San Francisco Bay as shipboard stowaways in the19th century, the invasive house mice have overwhelmed its steep, granite outcrops each fall.

Their numbers peak with the availability of food in late summer and fall, and then plummet into inescapable suffering and collapse.

At their height, the tiny rodents are “plague-like” — so numerous “the ground is seething” at night, according to ornithologist Peter Pyle, a research scientist who spent 20 fall seasons at the Farallon National Wildlife Refuge field station earlier in his career.

Official estimates put the peak population around 500 mice per acre, or 60,000 across the 120 acres that make up the southern islands. They are omnivorous, and ravenous, consuming plants and seeds, insects, amphibians, seabirds and even marine life.

When the food runs out, they turn on each other, die of starvation or cold, or succumb in flooded burrows.

This stark cycle of life and death, however, is not primarily what concerns the U.S. Fish & Wildlife Service, the federal agency in charge of the refuge, which is the largest seabird breeding colony in the lower 48 states.

Rather, it is their impact on other species and the ecological balance writ large that has divided conservation interests across the region, especially over the agency’s plan to poison the mice.

Saving the petrels

Using a strategy 17 years in the making, the agency hopes to shower the southern islands with 2,880 pounds of grain pellets laced with rodenticide in hopes of wiping out nonnative mice when they are at their lowest numbers at the end of 2022.

The model has been used around the globe to restore native ecosystems knocked off-kilter by invasive rats and mice.

The hope is the absence of mice will shore up populations of native cricket and salamander species found nowhere else on Earth, as well as save a rare island plant called maritime goldfield, which is threatened by invasive grasses spread by the mice.

But the main goal is to save a diminutive, smoke-gray bird called the ashy storm-petrel, a Fish & Wildlife “Bird of Conservation Concern” listed as endangered by the International Union for Conservation of Nature.

The stormy-petrel is considered at risk of extinction on the Farallones, where nearly 60% of the world’s declining breeding population once nested.

Many of the birds are eaten by burrowing owls that stop on the islands mid-migration to feast on the abundant mice.

Instead of moving on, a handful of owls stay through the winter, and once the rodent population crashes, they turn to the ashy storm-petrels.

Though the burrowing owls are few in number — conservatively 8 to 12 — they consume large quantities of petrels, which offer minimal nutrition, biologists say.

Some of the owls, also a California Bird Species of Concern, actually die of starvation, but not until after they have plundered the storm-petrel colony.

If the owls have no reason to stop — i.e., no mice — the hope is they’ll all move on and leave the petrels alone, proponents of the eradication plan say.

The world’s storm-petrel population, estimated at 8,000, is projected to drop more than 60% over the next two decades, said Pete Warzybok, who has spent more time on the island than anyone else as Farallones Program Leader with Point Blue Conservation Science.

Even the most ardent proponents admit that poisoning the rodents is not ideal. And they acknowledge there will be unintended deaths among other animals.

But the plan to save the storm-petrels and restore a healthier, more natural ecology is modeled on hundreds of similar operations they say have proven successful around the world.

“If we did not feel we could do this successfully, with minimal, non-target mortality, we would not do this project,” Refuge Manager Gerry McChesney said.

“The Farallones, it’s a very special place, and this is a project that we have been researching and planning for a decade and a half,” he said. “We’ve gone about it very carefully and methodically ... we didn’t want to leave any stone unturned.”

But some guardians of the coastal environment have been fighting the plan for years and will again when it comes before the California Coastal Commission on Thursday.

Two years ago, the federal agency withdrew a version of the plan after questions from commissioners. The plan has been updated to address concerns, and commission staff now recommends approval.



Critics, however, say the very idea of introducing a toxic substance into a marine sanctuary is abhorrent, especially a substance that is banned for sale in mainland California. They believe plans to reduce exposure to non-target species, such as hazing birds to keep them away, can’t possibly work.

Dogged by past failures

Others say the failure rate of other mouse eradication efforts is too high to justify the risk. They say Fish & Wildlife was too quick to reject alternatives, such as reproductive interventions or simply removing the offending owls each year.

Above all, they argue that plans to confine the bait pellets to the mice and to the islands are “implausible,” given the terrain, the elements, and the sheer number of creatures that would need to be kept at bay.

“The risks do not outweigh the benefits,” said longtime environmental advocate Cea Higgins, executive director of Coastwalk/California Coastal Trail Association and a member of the Greater Farallones National Marine Sanctuary Advisory Council. “I don’t feel they’re being completely honest about what the risks are.”

She and other allies point to hundreds of birds that died as a result of a 2008 rodent eradication that killed several dozen bald eagles on Hawadax “Rat” Island in the Aleutians. The island, however, now hosts more bird species than before, including nesting seabirds that had been driven out by rodents, U.S. Fish & Wildlife Service says.

“The heart of this whole dilemma is they picked the wrong chemical,” said Richard Charter, senior fellow with The Ocean Foundation and a longtime member of the Farallones sanctuary advisory council. “This is a chemical that just seeps out into the entire ecosystem so efficiently that there are warnings everywhere that you don’t ever use it near seabirds.”

Just 27 miles off the coast, the Farallon Islands erupt from some of the most productive waters on earth and support an especially diverse array of marine life. The National Wildlife Refuge is located in the Greater Farallones National Marine Sanctuary, and the islands are subject to State Marine Reserve and State Marine Conservation Area protections.

Often referred to as “California’s Galapagos,” the islands host more than 300,000 breeding birds from 13 species, the majority on the southern islands, which are also home to five marine mammal species: Northern Elephant Seals, Northern Fur Seals, California Sea Lions, Harbor Seals and Steller Sea Lions.

The Fish & Wildlife Service has selected a substance called Brodifacoum-25, an anticoagulant that causes animals that ingest it to bleed out. Its widespread use on the mainland has caused significant secondary poisoning in birds and mammals that ingest critters killed by it, prompting restrictions on its use.

The Farallon plan involves use of compressed grain pellets treated with a total 1.2 ounces of Brodifacoum, or about 0.0004 ounces per pound of bait. The pellets would be dispersed by helicopter and by hand in areas above the high tide line or otherwise unsafe to reach by air. Two aerial passes are expected, 10 to 21 days apart, in November and December, when the fewest number of birds and animals would be at risk.

Plans call for Western sea gulls and other birds to be hazed with noise to keep them away. Burrowing owls and peregrine falcons would be captured, held and relocated, and mice carcasses would be collected to prevent them from being eaten, though many are expected to die underground. Independent monitoring between applications would check for bait consumption by non-target species.

Supporters include Point Blue Conservation Science, which staffs the field station; the National Audubon Society and many local California chapters; the California Native Plant Society; the American Bird Conservancy; the Oceanic Society and others.

They dispute much of the critics’ concerns, saying they lack scientific basis — a charge made by both sides in the debate.

Biologist Gregg Howald, a British Columbia-based consultant to Fish & Wildlife, spent more than two decades with Island Conservation, a nonprofit dedicated to island restoration and eradication of invasive species. He said the bait is designed to break down in a matter of days, allowing the rodenticide to bind to organic materials in the soil, where it is broken down by microbes. It is not water soluble, he said.

He and McChesney said the bird losses on Hawadax led to improved mitigation plans for the Farallones. Howald added that any “spike into the ecosystem” of anticoagulant would be short-lived, unlike what’s happened with constant use on the mainland.

He said the overriding consideration is avoiding extinction, and that invasive species are implicated in 86% of recorded island extinctions.

“There’s a lot of news right now about the ecological moment that we’re in,” said Zach Warnow, director of communications for Point Blue. “We don’t see conservation opportunities come up like this very often, where a single action can have such powerful and long-standing impacts that can be help for generations upon generations on a human time scale.”

Bait by chopper

But there is substantial mistrust among the project’s numerous critics, in part due to what they deem to be overly rosy reviews of past operations.

Higgins, the Coastwalk director, said the need to disperse the bait by helicopter shows that the terrain is too difficult to ensure all dead mice are collected after they’re poisoned. She said it’s too likely gulls and migrating raptors might get to them first.

“I don’t put my foot down very often, but on this one, I’m fighting it all the way,” she said.

Former Central Coast Congressman Leon Panetta, who also served as White House Chief of Staff as well as secretary of defense and director of the CIA, weighed in last week with a letter to the coastal commission, citing his role as the author of legislation creating the Monterey Bay National Marine Sanctuary.

“Experimenting with a known multispecies poison already prohibited from retail sale in California ... simply does not make sense,” he said.

Howald said there’s a choice to be made.

“I understand the dilemma that people face with this, and people need to keep talking and asking questions,” he said. “But at some point, what we’re talking about is, ‘Are we going to prevent extinctions and enhance the resilience of these marine birds on the Farallones?’ It’s basically, ‘What do you want to choose?’ ”

You can reach Staff Writer Mary Callahan at 707-521-5249 or mary.callahan@pressdemocrat.com. On Twitter @MaryCallahanB.

Mouse Eradication Plan at the California Coastal Commission

California Coastal Commissioners are expected to hold a marathon hearing Thursday to determine if the U.S. Fish and Wildlife Service’s plan for poisoning invasive mice at the Farallon National Wildlife Refuge is consistent with policies in the California Coastal Act.

The virtual meeting begins at 9 a.m.

More information is available at coastal.ca.gov/meetings/agenda/#/2021/12.

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