The United States Department of the Interior’s Fish and Wildlife Service (USFWS) first proposed the “South Farallon Islands Non Native Mouse Eradication Project” in 2011 to eliminate a population overgrowth of non-native house mice (Mus musculus), probably first introduced to the islands in the 1800s.
They completed an Environmental Impact Statement in 2019 (download the PDF here), and came up with their preferred plan.
That plan is to air-drop a total of 2,917 pounds (that’s 1.3 metric tons) of toxic rodenticide pellets on the Farallon Islands to eradicate the non-native mice reported to endanger other species.
Because of the extensive experience we have with these poisons and their risks to wildlife, WildCare strongly opposes this action!
“Protect and Restore?”
The Project (quoting the Environmental Impact Statement from the United States Fish & Wildlife Service (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.”
To this end, the Service proposes three action alternatives their preferred of which they say “will provide a high likelihood of success based on similar projects elsewhere while minimizing incidental impacts to other resources.”
These alternatives are:
- Alternative A: No action
- Alternative B (preferred): Aerial broadcast of the rodenticide “Brodifacoum-25D Conservation”
- Alternative C: Aerial Broadcast of Diphacinone-50 Conservation
In 2013 when, with WildCare’s support, outrage against the proposal to blanket the islands with rat poison reached its peak, USFWS backed off from their proposal and promised to complete the EIS before further action was taken.
Unfortunately, the report still came back with only those same two alternatives given— to dump rodenticide all over the islands, or to do nothing about the mouse infestation.
The only alternatives?
WildCare does not believe these are the only options open to the USFWS to control rodent populations on the Farallon Islands, and the problems with these “action alternatives” are manifold:
1. The Farallon Islands are an incredibly sensitive environment. Anything that happens on any of them will affect everything on the island(s) and in/throughout nearby waters. These islands are also not far from San Francisco, Marin and Sonoma Counties, which means that animals that come into contact with the poisoned bait on the islands will sicken or die on the mainland, exposing more wildlife to the risks of secondary poisoning.
2. Brodifacoum is toxic to birds, mammals and aquatic life (this is according to the product label, read it here) and is an extremely dangerous and persistent environmental poison. Brodifacoum persists in the soil for 120+ days, and it can persist in the livers of exposed animals for over 200 days (more than eight months!)
In fact, the California EPA has banned the sale of rodenticides containing brodifacoum to consumers because of its toxicity and the dangers to non-target wildlife. Registration for these toxic poisons has also been cancelled on the federal level.
Proponents of the USFWS plan insist that island conservation is different, and that poison should be allowed in this situation because it is unique. WildCare says that everyone thinks their poison situation is unique! People think “it’s just my backyard.” “It’s just my neighborhood park.” But what they don’t realize is that every other person has come to the same conclusion, and that means these dangerous and deadly poisons are everywhere in our environment.
In this case, officials are thinking “It’s just the Farallon Islands,” but this is a terrible precedent to set in the San Francisco Bay Area. Poison is the easy way out, but the easy way is not always the best way. A sustained rodent control campaign on the islands would help threatened seabirds, reduce the impacts of the mice on native vegetation and endemic wildlife and eventually rid the island of the mouse problem. But it wouldn’t be easy. Solving nuisance wildlife problems the environmentally responsible way rarely are.
3. Non-target predator animals will consume the rodents that have eaten the pellets and be poisoned too.
The document “Rat Island Rat Eradication Project: A Critical Evaluation of Nontarget Mortality” (click to read the PDF) outlines the unintended consequences of this type of eradication project. Quoting from the document:
“Some nontarget mortality was expected, but the actual mortality exceeded the predicted mortality. Forty six Bald Eagles died (exceeding the known population of 22 Bald Eagles on the island); toxicological analysis revealed lethal levels of brodifacoum in 12 of the sixteen carcasses tested.”
Over the past decade, WildCare has tested hundreds predatory patients in our Wildlife Hospital for exposure to rodenticides from having eaten poisoned rodents. A shocking 76% of tested patients test positive, and many of these patients died from their exposure. Our research demonstrates conclusively that non-target animals can and do die from eating rodents that have eaten poison. These toxins are persistent in the environment and deadly; they should not be used in massive quantities in national wildlife refuges.
4. Non-target species will consume the pellets. The document about the Rat Island project, “Critical Evaluation of Nontarget Mortality” (PDF), further demonstrates that, while most poisoning of non-target animals resulted from predation upon bait-poisoned rodents, gulls and other animals were found to have also consumed the pellets and to have died from primary poisoning from brodifacoum.
The Environmental Impact Statement released by USFWS for the “South Farallon Islands Invasive House Mouse Eradication Project” discusses the impact of this plan on non-target animals in terms of overall population impact. Under “realistic” conditions, the number of dead gulls allowable to prevent impacts on overall population is just over 1,000. With this number of gulls killed, their modeling predicts that Western Gull populations after 20 years would be about the same whether or not the project goes forward.
That number is considered the “acceptable” number of birds that could die from the poisoned bait. Whether or not 1,000 gulls actually die if this plan is carried out, the fact that it allows for as many as 1,000 poisoned gulls that could fly to and die on Marin, Sonoma and San Franciso beaches, that will be eaten by marine mammals and other marine species, and by land-based predators, all of which will also be poisoned, is not “acceptable” to WildCare.
5. WildCare believes a plan to “haze” gulls away from the islands prior to the dumping of the poison won’t work. The idea that the agency can “haze” gulls away from the island prior to the dumping is ludicrous to anyone who has ever tried to shoo a gull away from a picnic site. The birds may be temporarily deterred, but they will come back.
Rodents that have consumed brodifacoum do not die immediately. They can live for days after taking their first deadly dose of rat poison, slowly weakening from internal bleeding and dehydration.Sick and dying rodents make easy prey, and their thirst and disorientation means they will be ready meals for opportunistic Western Gulls that will take advantage of such a smorgasbord of easy-to-catch prey.
Tests done by USFWS to determine the efficacy of gull hazing methods were incomplete as the tests did not include dumping 2,917 pounds of edible bait on the islands, nor did they arrange for thousands of dying mice to be present. Gulls may be deterred when there are not two readily-available food sources available (the bait and the dying mice), but any analysis of gull behavior near a food source demonstrates that deterrents will likely be less effective than anticipated.
Hazing will not deter gulls from ingesting poison, or from ingesting poisoned rodents.
6. The mice aren’t themselves the primary danger to the seabirds that nest on the island. The large numbers of mice on the islands have attracted 6 – 8 non-resident predators, including a population of Burrowing Owls, a threatened species on the mainland. Annual cycles cause the mouse populations to rise and fall, and when mouse populations plummet, the seabird nestlings become the prey of these raptors. Ashy Storm Petrel chicks are consumed by opportunistic Burrowing Owls, but should the entire ecosystem be blanketed in toxic rat poison to prevent this? Surely there is another way!
The fact is, this situation has existed on the South Farallon Islands for decades. WildCare and our allies do not disagree that the mouse problem needs to be dealt with. What we disagree with is that the only two alternatives to help and protect the fragile ecosystem on the Farallon Islands are to a) do nothing or b) drop 2,917 pounds of poisoned bait on the islands. We also disagree that the potential for significant collateral damage to non-target wildlife doesn’t matter.
About “Brodifacoum-25D Conservation”
In WildCare’s Wildlife Hospital, dozens of animals each year die from pesticide poisoning. Our multi-year initiative to test rodent-eating animals admitted to the hospital for rodenticide levels show varying levels of rodenticide residue in hundreds more patients. Read more about WildCare’s work to combat rodenticides here.
The majority of poisoned patients, however, are not the targeted pests like rodents; they are instead the predators that eat the poisoned rodents. This is called secondary poisoning, and is a harsh reality of pest eradication programs such as this one.
USFWS claims the “conservation” variety of the second-generation anti-coagulant rodenticide brodifacoum is less harmful to non-target species (i.e. every animal on the islands other than the mice). WildCare’s experience and information show this to be untrue– Brodifacoum is one of the most toxic, dangerous and persistent rodenticides available, and the amount of active ingredient in the “Conservation” variety differs only slightly from that in the full-strength product.
Arguments in favor of this proposal overwhelmingly focus on the necessity to protect the many endemic species and species of special concern that live and breed on the Farallones. It is WildCare’s position that, if control of House Mouse populations is necessary, responsible, non-toxic and environmentally sustainable approaches must be used.
The aerial broadcasting of toxic rodenticide pellets over the entire landmass of the Farallon Islands does not fit these criteria and should not even be considered in the eradication proposal.
How You Can Help
Stay tuned! We’ll let you know when the proposal will once again be in front of the Coastal Commission or another regulatory body and we’ll have a letter you can personalize and send.
Spread the word! Share this page on Facebook and give friends the information too! We cannot allow this highly irresponsible approach to nuisance rodent control move forward!