Close to Home: Eradication of mice on Farallon Islands is right move

I would like to respond to Richard Charter? Close to Home ("Farallon Islands ecosystem at risk," Dec. 8.)

I am a wildlife researcher who spent parts of 24 years as a biologist on the Farallon Islands, including more than 20 fall seasons when the invasive house mouse population there explodes and crashes each year. I am usually against the use of chemical agents in the environment, but the long-term benefits of a successful mouse eradication on the Farallon ecosystem so vastly outweigh the costs of a single application of brodifacoum that it is greatly worth an attempt.

Use of a chemical in the environment is an easy subject to get the public worked up about. In this case, Charter and others have done an admiral job of recruiting opinion against an eradication attempt from a lot of people who have never been to the Farallones, have not read the U.S. Fish and Wildlife's exhaustive draft environmental impact statement on the project and are forming an opinion without full consideration of the scientific facts or long-term trade-offs of an eradication attempt. It is easy under such circumstances to have the public believe false and distorted scientific information, as seems to be occurring to some extent with the review process of this project.

By reading the environmental statement, a 700-page document (available online) in which the U.S. Fish and Wildlife Service provides great detail on rodent eradication from islands and alternatives for controlling or removing mice from the Farallones. You will learn that:

Each fall, the mouse population reaches plague-like densities of more than 490 mice per acre and some 60,000 to 100,000 mice overall, after which the population crashes to hundreds, at most, in spring. Populations with this sort of extreme and unbalanced annual cycling cannot be eradicated or controlled at low levels through trapping or other means.

The mouse crash results in considerable suffering for tens of thousands of mice each year, including hypothermia following winter rains and widespread cannibalism. Those against animal suffering should be for eradication to end this gruesome annual destruction.

Migrating burrowing owls will not remain on the island once mice are removed. Storm-petrels are essentially absent from the Farallones from November to February, there is nothing else, besides mice, for arriving migrant owls to eat during this period, and they will continue migrating as do thousands of other migratory birds that stop over on the Farallones each fall. Currently, many or most wintering owls die there in spring, as even the presence of storm-petrels, in the absence of mice, is not enough to sustain them for spring migration. Thus, both owls and storm-petrels die unnecessarily every year due to the mice.

The application would take place in November or December, during and after the mouse population crash, and when less than 1 percent of the breeding seabirds (including gulls) are typically present on the islands. Owls will be trapped and relocated to the mainland before application.

In saltwater, brodifacoum will dissolve within two to three hours and, at the very low quantities expected to reach the Farallon marine environment, will be undetectable in the turbulent ocean there within a day, if not a few hours. Those against pesticide use would do much better to focus on pesticide and herbicide use on farms and lawns, or tenting of houses for termites, rather than the much-lower-impact, one-time application of brodifacoum on the Farallones.

Brodifacoum has been used to successfully eradicate rodents from more than 50 other islands, in most cases, no or only minor incidental death occurred, and each trial results in more data and improved knowledge to limit non-target ingestion during future applications.

I liken the trade-offs to a marble of single-time cost within a living room of permanent benefit. I urge those interested or concerned about this issue to become better-informed of the scientific facts and to carefully consider the big picture before commenting against the project.

Peter Pyle is a research biologist for the Institute for Bird Populations at Point Reyes Station.