South Farallon Islands are the Most Rodent-Dense Islands in the World

Posted on August 19, 2013

The South Farallon Islands, a National Wildlife Refuge, are located about 27 miles off San Francisco. They are the most rodent-dense islands in the world. The massive mice population is threatening some of the other species on the islands.

Anne Morkill, manager of the San Francisco Bay National Wildlife Refuge Complex, which includes the Farallon Islands, said in a release, "Invasive house mice are taking a serious toll on the seabirds and other wildlife of the Farallon Islands. The ecosystem on the islands is out of balance. We want the public to give us feedback on our proposals for eradicating the mice and restoring that balance."

USA Today reports that scientists studying the island say there are so many mice on the islands that the ground often appears to be moving. There are estimated to be 60,000 mice on the islands, which is about 500 mice per acre. reports that there are basically two options for dealing with the mice population on the island. One option is two drop deadly poison (food pellets soaked with anticoagulants) on the mice from a helicopter. The other option is to do nothing at all. The options were listed in a 650-page report from the U.S. Fish & Wildlife Service that analyzed 49 different mice removal alternatives.

Some of the ideas not recommended include bringing in falcons, feral cats or snakes. Trapping the mice and using fertility drugs were also ruled out.

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