Alison Hawkes in Bay Nature:
Every year, as summer turns to fall, the mouse population on the South Farallon Islands explodes to plague-like densities, numbering 490 mice per acre, among the highest found on any island in the world. The scientists who live and work there describe the assault of the invasive house mouse as a kind of purgatory in the otherwise stunning, windswept smattering of rocky islets and sea stacks 30 miles outside the Golden Gate.
“At night they would be everywhere,” says Peter Pyle, a wildlife biologist who spent more than 20 fall seasons living at the research station on Southeast Farallon Island. “I had them crawling on top of me at night and in my hair. I tried to mouse-proof the house but we’d catch 50 mice in the night.”
Besides making scientific research on the Farallones a harrowing experience, the common house mouse, Mus musculus, has substantially disrupted the island ecosystem — spreading the seeds of invasive plants, eating the endemic Farallon camel cricket as well as a species of daisy called maritime goldfields that provides critical nesting material for birds, and indirectly causing the demise of the island’s breeding population of ashy storm- petrels, a California bird of special concern.
It’s a familiar story on islands all over the world where rodents — prolific feeders and breeders — are a leading cause of extinctions. Massive efforts have been undertaken to kill invasive rodents and usually involve broadcasting rodenticide; other options, like trapping mice or releasing biological controls in the form of snakes or cats, have been ineffective.