A federal study says the only way to eradicate the nonnative mice infesting the sensitive Farallon Islands is to shower the islands with powerful rodenticides by helicopter.
On Friday the U.S. Fish and Wildlife Service released a report analyzing alternatives for killing the mice that exist at densities of 500 mice per acre.
The San Francisco Chronicle reports that it's the highest density of island rodents in the world.
The mice eat the same food as the Farallon arboreal salamander. Brought on ships by 19th-century seal hunters, the mice are the last nonnative mammals on the islands 27 miles west of San Francisco.
The plan would involve air drops of poisoned food pellets.
Animal welfare groups have opposed the idea of air drops on the islands.