Farallon Islands

Poison Proposed to Fight Rodent Infestation on the Farallon Islands

By Thomas K. Pendergast

Part of the Richmond District is overrun with mice and the federal government has offered a plan to eliminate the rodent infestation by dumping more than a ton of grain laced with poison out of a helicopter on the rodents’ environment. 

Sitting 27 miles west of San Francisco, the Farallon Islands are officially considered a part of the City and County of San Francisco, and is included in Supervisor District 1, a.k.a. the Richmond District. 

Other than authorized personnel, no humans are allowed on the islands because they are a nesting area and bird sanctuary. The authorized personnel would be members of the National Park Service (NPS) – U.S. Fish and Wildlife Department, because the feds actually take care of the islands.

But there are many other “unauthorized” residents on the more than 141 acres sitting above the waterline: mice, lots and lots of them.

It is suspected that the rodents have been there since the 19th century when they jumped off fishing or whaling boats. And since then they have been a threat to native species, like the Ashy Storm-Petrel bird. According to the NPS, about half the world population of this species breeds on the South Farallones.

The Leach Storm-Petrel will also likely benefit from a mice eradication, although that bird is more abundant elsewhere. The NPS also says removing the mice would dramatically reduce predation by burrowing owls on the Storm-Petrels and that is indirectly related to the mice.

In the fall, mice attract migrant owls that stay on the islands through the winter. When that food source gets scarce they switch to the Storm-Petrels. 

The Farallon arboreal salamander and the Farallon camel cricket are found there and nowhere else. Mice compete with the salamanders for prey and they eat lots of maritime goldfield, an annual plant endemic to seabird nesting islands along the coasts of California and Oregon, and its largest population is on the South Farallones.

Last month, U.S. Fish and Wildlife officials withdrew their plan to drop poison on the mice, which was designed to rid the islands of them in an effort to restore the natural ecosystem on the islands, part of the Farallon Islands National Wildlife Refuge. 

The plan involves dropping more than a ton of cereal or grain pellets laced with rat poison on the islands from helicopters. But questions arose about the plan when it went before the California Coastal Commission (CCC), which apparently motivated federal officials to take it back to the drawing board and have another look before resubmitting it later.

“Fish and Wildlife basically pulled the application,” CCC spokeswoman Noaki Schwartz said. “The commissioners had quite a few questions, so they’re going to kind of go back and try and answer some of these questions and then resubmit their application. So, bottom line, there were no decisions made.”

She noted that Fish and Wildlife does not need the CCC’s approval but was looking to get the commissioners’ opinion on the plan. 

“I think they really want to work with the commission on this,” she said. 

Wildlife advocates were pleased nonetheless. 

“Dropping 1.5 tons of poison on a national refuge … is to me, a catastrophe,” said Kimberley Fitts, a wildlife biologist with a degree in zoology. “The terrestrial species that I do work with, every time there’s a necropsy, the levels of rodenticide poison is sky high. It’s already in the food chain … I just think it’s a terrible decision.”

WildCare is a wildlife hospital and nature education center located in San Rafael that treats as many as 4,000 animals each year. 

“For the past 10 years we have been doing extensive testing to see what the impacts are of this particular type of rat poison, the second-generation anticoagulant rodenticides, to see what the impacts are of those poisons on wildlife and … 76 percent of the animals that we tested came back with positive results for having these rat poisons in their systems,” WildCare’s Director of Communications Alison Hermance said. “So, WildCare sees on a regular, if not daily. basis the impact of these poisons. 

“I have personally stood in our medical room and watched a red-tail hawk die from bleeding out, from having consumed poison that rodents had eaten the very same poison they’re talking about dumping on the Farallones. We see, every day, the impact of these poisons on non-target animals and we just cannot justify their use in such a fragile and significant habitat,” she said. 

But NPS officials say do not believe the hype about the rat poison, as most of the 1.5 tons of the pellets they would drop consists of grain or cereal filler. 

“We’re talking about one-and-a-half tons of bait pellets,” said Doug Cordell a spokesman for the U.S. Fish and Wildlife Service. “So most of that, overwhelmingly, is basically cereal. The actual amount of rodenticide is less than one-and-a-half ounces. So it’s a big difference.”

He said at a July 10 meeting the CCC board members questioned him mostly about the actual implementation plans and contingency plans, wanting details for those as well. 

“For right now, we have not abandoning this plan at all. We’re moving ahead but we want to get a consist determination from the Coastal Commission,” Cordell said. “We want to work effectively with the state. And we said to the commission, ‘We want to withdraw this application for now … and we’re going to work with your staff and with the commissioners to get you the answers you’re looking for, as best as we can, and we’re going to come back in a few months and reapply.’”

“And this (rodenticide) is the only method in the field to do it. It’s the only way,” he said. “There are some experimental methods out there with fertility control and genetic alteration of mice, introduction of biological disease, these kind of things. They are all in the experimental phase; they have not been proven in the field, and they can have very unintended consequences on other wildlife if something goes wrong.”

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