Islands are special
In contrast to continents, their ecosystems have much fewer moving parts. It’s not unusual for an island to have only a few plant species and often no land bird or mammal species. All of New Zealand has no native land mammals except for bats. The Channel Islands off southern California have only a native deer mouse and the island fox, and that’s only on some of the islands. Southeast Farallon Island has no native land mammals.
Yet islands are critical refuges for marine mammals and seabirds. It’s not unusual for over 90% of a single species to come from a single island, or just a few islands. For example, over 99% of the world’s Heermann’s Gulls breed only on Isla Raza, a 1.5 acre postage stamp in the Sea of Cortez. 95% of the world’s Black-vented Shearwaters breed only on San Benito Island off Baja California. 99% of the world’s Scripps’s Murrelets come from four islands off southern California and Baja California. And probably 50% of the world’s Ashy Storm-Petrels nest in burrows on a single hillside on Southeast Farallon Island. There are similar examples from all over the world.
Islands are vulnerable
This gets us to the final characteristic about islands; they are vulnerable to perturbations. Add one more moving part, and things can fall apart quickly. 75% of all bird, mammal, amphibian, and reptile extinctions have occurred on islands. More bird species have gone extinct on the Hawaiian Islands than on North America, South America, Europe, Africa, Asia, and Australasia combined.
The introduction of a single non-native species, such as rats or mice or cats or even rabbits, can result in massive changes to an island’s ecology, leading to the extinction of native or breeding species. Rats, arriving as stowaways on ships, are the number one cause of bird extinctions worldwide.
When I worked for the California Department of Fish and Wildlife, I was involved in over 300 restoration projects. The best one, the one with the most obvious and dramatic benefits, was when we eradicated non-native black rats from Anacapa Island. In addition to benefitting Scripps’s Murrelets, other seabirds such as Cassin’s Auklets began nesting on the island. The native lizard and even the sea stars and mussels and vegetation rebounded; the rats had been eating them all out of house and home.
The mouse problem on Southeast Farallon Island
Today, the non-native house mouse is impacting the Farallon Islands, one of the most important seabird nesting colonies south of Alaska.
Southeast Farallon Island, the main island, is infested with the mouse. In fact, there are higher densities of house mice there (more than one per square foot) than anywhere in the world. They eat seabird eggs and spread the seeds of non-native weeds around the island. More significantly, they attract a few migrating Burrowing Owls each fall. The owls, lost over the ocean, would normally stop on the island and then leave. But with the mice there, the owls stay and feast. When the winter rains come, the mouse population crashes and the owls begin to starve. Right about then, the declining Ashy Storm-Petrels begin returning to the island to nest. The owls catch them and stack them like cordwood. (In the most recent review, they were not listed an “endangered” based on the assumption that this project would be implemented.)
One thing to know about Ashy Storm-Petrels is that they are long-lived and slow-reproducing, like most seabirds. With the owls killing the adults, the storm-petrel population cannot recover.
Eventually, the owls starve to death. Then the mouse population rebounds in the spring and the cycle starts over, while the storm-petrel population spirals down. This happens every year on the Farallones.
Restoring the island thru mouse eradication
The plan is to eradicate the house mouse from Southeast Farallon Island, as we eradicated rats on Anacapa, and as has been done on over 600 islands worldwide.
The key is to get every last mouse—thousands of them. The only way to do this is to use rodenticide bait pellets. It will be done in the late fall, when the mouse population is at its low point, and when there are very few birds or mammals on the island. The few gulls present can be hazed with a laser (we’ve tested this). Any pellets that fall in the water will quickly decompose. On Anacapa, there were few secondary impacts; the benefits were far greater than we ever dreamed.
This project has been researched by dedicated biologists who know and love the island. We have explored all alternatives. (Contraceptives are not feasible. Introducing more raptors is NOT the answer.) We have researched possible harms and benefits. We’ve seen the amazing restoration of the ecosystem on Anacapa and on 600 islands worldwide, and we’ve worked with experts from New Zealand.
Here is a list of organizations and experts in support of the project:
- National Audubon Society
- Audubon California
- American Bird Conservancy
- BirdLife International
- The Nature Conservancy
- California Native Plant Society
- California Invasive Plant Council
- David Ainley; author of Seabirds of the Farallon Islands; Ashy Storm-Petrel species account in Birds of North America
- Peter Pyle; Institute for Bird Populations; author of Identification Guide to North American Birds and over 100 journal articles
- Peter Harrison; author of Seabirds: An Identification Guide.
- Mark Rauzon, Marine Endeavors; author of Isles of Amnesia: The History, Geography, and Restoration of America’s Forgotten Pacific Islands.
- Hadoram Shirihai, Tubenoses Project; author of A complete guide to Antarctic wildlife: the birds and marine mammals of the Antarctic continent and the Southern Ocean; Whales, dolphins and seals: A field guide to the marine mammals of the world; The Macmillan birder’s guide to European and Middle Eastern birds.
- Debi Shearwater, Shearwater Journeys, 44 years of offshore experience; co-author of Distribution patterns and population size of the Ashy Storm-Petrel
- Dianne Feinstein, US Senator
- Point Blue Conservation Science (formerly Point Reyes Bird Observatory)
- Institute for Bird Populations
- Pacific Seabird Group
- Agreement on the Conservation of Albatrosses and Petrels
- Island Conservation
- California Academy of Sciences
- California Institute of Environmental Studies
- Oiled Wildlife Care Network
- International Bird Rescue
- Golden Gate Audubon Society
- Marin Audubon Society
- Monterey Audubon Society
- San Diego Audubon Society
- Sequoia Audubon Society
- Marin County Supervisor
- Santa Cruz County Supervisor
- National Refuge Association
- Save the Bay
- Farallon Islands Foundation
- Citizens Committee to Complete the Refuge
- Coastal Conservation Action Lab
- Freshwater Life
- Marin Conservation League
- Marine Endeavors
- Natural Heritage Institute
- South Georgia Heritage Trust
More details about the project and the public process
More details about the project, the process, and all relevant documents can be found here. The project will come before the California Coastal Commission on Dec 16, 2021. Letters to the Commission should be emailed to email@example.com. The deadline for letters is 5pm on Friday, December 10.
Related reports and videos
Here are some videos and reports about past similar projects:
Anacapa Island Rat Eradication
Short documentaries/reports of rodent eradications from islands around the world