South Farallon Islands Invasive House Mouse Eradication Project

The Farallon Islands, part of San Francisco, are home to the largest colony of nesting seabirds in the contiguous United States. Credit Joshua Hull/U.S. Fish and Wildlife Service.

Located nearly 30 miles off the coast of San Francisco, Farallon Islands' craggy peaks and rocky shorelines are home to the largest colony of nesting seabirds in the contiguous United States. Credit Joshua Hull/U.S. Fish and Wildlife Service.

The United States Fish and Wildlife Service (USFWS) proposes to eradicate invasive, introduced house mice (Mus musculus) from the South Farallon Islands and eliminate their negative impacts to the ecosystem of the Farallon Islands National Wildlife Refuge.


Join the Marin Audubon Society on July 16, 2020, 7:00 PM PST, for a webinar to learn more about the South Farallon Islands Invasive House Mouse Eradication Project.

The webinar will be via Zoom; registration is required.

Please click here for the webinar:

Presentations will be made by scientists and land managers experienced with the Island's wildlife and the Restoration Plan:

* Gerry McChesney, Farallon Islands National Wildlife Refuge Manager, U.S. Fish and Wildlife Service
* Winston Vickers, DVM, MPVM, University of California, Davis
* Peter Warzybok, Farallones Program Leader, Point Blue Conservation Science
* Roger Harris, Certified Wildlife Biologist, Oceanic Society
* Anna Weinstein, Ocean Resources Director, National Audubon Society, as MC

About the South Farallon Islands Invasive House Mouse Eradication Project

USFWS's goal is to protect, inventory, and monitor, as well as to restore to historic levels, breeding populations of 12 seabird species, 5 marine mammal species, and other native wildlife of the Farallon Islands National Wildlife Refuge.

One of the strategies identified to meet this goal is the eradication of the non-native invasive house mouse from the South Farallon Islands, and the prevention of future introduction of mice.

USFWS expects that eradicating invasive mice will benefit native seabirds, amphibians, terrestrial invertebrates, plants, and wilderness quality, and will help restore natural ecosystem processes on the islands.

The South Farallon Islands have sustained ecological damage over many decades from the presence of invasive mice. Eradicating house mice would eliminate the last remaining invasive vertebrate species on the Refuge, thereby enhancing the recovery of this unique and sensitive ecosystem.

The South Farallon Islands are a national wildlife refuge that hosts the largest seabird breeding colony in the contiguous U.S. About 350,000 seabirds from 13 species use the island, including about half of the world’s population of ashy storm petrels. The mice, believed to have been introduced by ships in the 19th century, have been wreaking havoc on the island’s ecosystem in a variety of harmful ways, according to the USFWS.

In addition to eating the seed bank for native plants, competing for food of island-specific species and even eating eggs and chicks of some of the nesting birds, the mice attract predatory burrowing owls to remain longer than normal on the island, the agency states. Normally, the owls stay for a few days on the islands for their fall migration, according to the Point Blue Conservation Science group, which has been monitoring birds and wildlife on the islands for about 45 years and provided data that is used in the USFWS proposal. But the mice provide an ample ongoing food source, incentivizing owls and other raptors to stay for weeks. When the mouse population crashes during the winter months due to low food supply, the owls turn to the ashy storm petrel as their new food source.

Each of the six to 12 owls that inhabit the islands during the winter can kill 60 to 70 petrels including breeding petrels, which has an impact on the population, according to a Point Blue study released last year. There are an estimated 5,000 to 10,000 breeding ashy storm petrels in existence, according to the study. Point Blue’s study states removing the mice would have a significant impact on restoring the petrel population.

USFWS proposes to airdrop and hand place 2,917 pounds of cereal pellets laced with a rodenticide on the 10 rocky islands and islets of South Farallon Islands to eradicate an estimated population of 60,000 mice.

Around 50 other eradication methods were reviewed by the USFWS as part of its environmental review including contraceptives, individual traps and pathogens. They were either deemed infeasible or inadequate to stop the mouse problem.

Several conservation groups, including California Audubon, the American Bird Conservancy and Point Blue Conservation Science, support the poisoning technique, which has successfully eradicated rodents on islands in Mexico, the Caribbean, the South Pacific, the Aleutians and the Galapagos chains, and the Channel Islands in California.

Further Reading

* Slideshow that has an overview of the South Farallon Islands Invasive House Mouse Eradication Project in partnership with Island Conservation and Point Blue Conservation Science. (Note: The date for providing public comments is past.)

* Final Environmental Impact Statement of the South Farallon Islands Invasive House Mouse Eradication Project released by US Fish and Wildlife Service on 03/15/2019.

* Meet the Farallon National Wildlife Refuge! A 2016 blog post by Ross Nichols, a Point Blue biologist who chronicles his perspectives and experiences from working on the Farallon National Wildlife Refuge. The U.S. Fish and Wildlife Service manages the Farallon National Wildlife Refuge with cooperation from partners at Point Blue Conservation Science (Point Blue).

* At Farallon Islands, man meets nature, on nature's terms. Bonnie Tsui writes in the New York Times Sunday Travel section "People commute mindlessly over the Golden Gate Bridge day after day without realizing that whales, sea lions, seals and harbor porpoises congregate here still. Venture a little farther out from shore, to the Farallon Islands, and you get a sense of what it was like to truly feel wild, remote, at sea."

* For those at home, sheltering in place, now enjoy a live stream of the the Farallon Islands National Wildlife Refuge via a newly restored, high-definition webcam on a lighthouse atop Southeast Farallon Island.

The webcam is a partnership of the U.S. Fish and Wildlife Service, Point Blue Conservation Science, and the California Academy of Sciences.