Every day we face tradeoffs concerning our own and our environment’s wellbeing. Do we fly back to New York for Christmas despite the chances of a plane crash, catching the flu or adding to our carbon footprint? Are the conveniences of driving to Fairfax as opposed to taking the Stage, or of buying and powering a computer, worth the pollutants added to the environment through those actions? Most of us would say yes, but balancing tradeoffs is not always simple—which is why Wall Street investors spend so much money on comprehensive cost-benefit analyses.

The United States Fish and Wildlife Service is currently considering a tradeoff in an effort to restore the health of the Farallon Islands, where non-native house mice are disrupting the natural balance of the ecosystem. The mice are indirectly contributing to the annual loss of migrating burrowing owls, breeding ashy storm petrels and other creatures. 

Does the federal government remove the mouse population at the cost of using a toxic rodenticide? Fish and Wildlife has prepared a more than 700-page draft environmental impact statement to assess this proposal in a cost-benefit manner. The benefits are substantial. 

Currently, as non-native vegetation seeds, the house mice population explodes and then crashes in late fall. Approximately 60,000 mice suffer from hypothermia, starvation and cannibalism each year. Migrating owls are coaxed to remain on the islands by this food source, many to starve after the crash, others to prey on the storm petrels that arrive in March. Even after killing a dozen or more petrels, few owls likely survive until their spring migration. 

Without the mice, the owls will not remain. Removing the mice should also help control or eliminate non-native vegetation, such as Ehrharta and Bromus grasses, which currently block breeding seabirds from constructing burrows on the island. Best of all, these benefits will be long-term, or even indefinite. 

Under the preferred alternative, the costs would be the application of between 1.16 and 1.54 ounces of a toxic rodenticide called brodicafoum. In a worst-case scenario, this toxin might kill up to a few hundred gulls and two or three owls that eat the dead mice. It might also leach into the marine environment and be detectable for a day or two. Another risk is that the application will not be successful, in which case we will have wasted time, money and possibly the lives of non-target species.

I believe these short-term costs and risks are worth the potential long-term benefits of a successful eradication, and I think even Wall Street analysts would agree. 

With close attention to weather patterns and by following the mitigation measures detailed in the draft environmental impact statement, non-target injury to birds and other wildlife can be greatly reduced from the worst-case scenario. To help manage the primary risk of non-target death, owls will be relocated to the mainland before the rodenticide is applied. Gulls will be hazed, or scared away, for two weeks or more following the application. (The gulls present in fall and early winter—less than 1 percent of the breeding population—are skittish, just as they are on local beaches.) 

The ocean surrounding the Farallones is incredibly turbulent and will quickly dilute any brodifacoum that reaches it. Application of this rodenticide has been tried on at least 66 islands and has been effective in eradicating rodents 47 times. Through trial and error, the success rate has improved steadily with time. 

Let’s also put the costs into perspective. One-tenth of a pound of brodifacoum will be dispersed in one to two tons of grain-based mouse pellets. (Detractors of the project refer to this as “one to two tons of rodenticide”). By comparison, in 2011 alone, Marin County reported the application of 64,525 pounds of pesticides, largely for farming or industrial uses or to remove “pests” from our houses and yards. Additionally, a 2006 county report indicates that the average Marinite’s carbon footprint is higher than that of the average Californian or North American, about twice that of Europeans, and over 10 times that of the average world citizen. Our use of cars and energy amounts to over 1 million tons of CO2 released in the county every year. And road-kill statistics suggest that roughly 31 animals are killed every day in Marin. This amounts to more than 11,000 animal lives a year, largely for our convenience and personal pleasure. Should we ban cars from Marin?

For those who understand these tradeoffs and are still against attempting to eradicate mice from the Farallones, well, I salute you. Assuming, that is, that you have eliminated convenience driving and electricity from your lives such that your annual personal polluting of Marin will be lower than the one-time cost of a rodenticide application on the
Farallon Islands. 


Peter Pyle has lived on the Farallones for more than 20 fall seasons. He lives in Bolinas and works for the Institute for Bird Populations in Point Reyes Station.