The US Fish & Wildlife Service (Service) released a draft Environmental Impact Statement (EIS) last Friday, August 16, 2013, outlining three alternatives for dealing with invasive mice that are negatively impacting wildlife and the ecosystem on the Farallon Islands. The EIS recommendations originate from the Service’s 2009 Comprehensive Conservation Plan (CCP), which concluded that invasive house mice are adversely affecting rare seabirds, including the ashy storm petrel, by attracting burrowing owls that prey not only on mice but also on these rare seabirds. Currently, the Service is accepting public comments on the EIS through September 30, 2013.

Alternatives Proposed by the Service’s EIS

After assessing a total of 49 potential mouse removal options, including non-chemical alternatives, the Service offered the following: (1) taking no action, and (2) aerial broadcast treatments of Brodifacoum 25D-Conservation or Diphacinone 50D-Conservation over the Farallons to eradicate the mice. Other options like traps or targeted poisoning were eliminated from full consideration due to the island’s steep and rocky terrain. Eradicating non-native mice in such a setting made these methods technically and economically infeasible. Brodifacoum and Diphacinone, both anti-coagulant rodenticides, are intended to kill mice by causing internal bleeding but can also kill any animal that consumes the poison or a poisoned rodent. The consideration of rodenticides in wildlife management might be surprising; however, the use of poisons for conservation purposes is sometimes utilized to protect rare species and sensitive ecosystems from invasive rodents.

What are the Implications of Each Proposed Plan?

Proponents of rodenticide use as described in the EIS argue that, while consumer and agricultural use of rodenticides can be harmful to children, pets, and wildlife, these poisons can prevent species extinction and restore sensitive ecosystems plagued by invasive rodents. Additionally, proponents says that careful application of rodenticides by trained professionals, along with other mitigating steps such as removal of owls during treatment, can reduce risks to non-target wildlife. The primary concern with this approach is that poisonings of non-target wildlife will be unavoidable. Alternatively, taking no action would maintain the existing high densities of the non-native house mice and vagrant burrowing owl population, which will continue to threaten rare native sea birds and other wildlife. For more information on the use of rodenticides for island conservation efforts, please visit the USDA Wildlife Damage Management page.