All the islanders are associated with the cooperative, which has exclusive fishing rights to the island, recognized by the federal government. It is not uncommon for fishermen to bring domestic cats to Natividad Island as a way to control the native mice that are attracted to their houses. Unfortunately, when the cats prove to be poor mouse hunters, fishermen usually abandon them. When we arrived three years ago, a distinct population of wild cats roamed the island. Historical notes by other scientists and naturalists report feral cats here as far back as the early 1900s.
Feral cats are a leading cause of bird and mammal extinctions on islands all over the world.
On Natividad Island we witnessed nightly killings over the past three years, and it was quite clear that cats were the single greatest threat to the health and persistence of black-vented shearwaters. They were killing hundreds of birds a week as well as preying on other species native to the island. Over 75 percent of all recorded animal extinctions have been island endemics, the majority as a direct result of introduced species. Predators, such as feral cats and rats, prey on native fauna and extirpate nesting seabird colonies. Introduced herbivores, such as European rabbits, sheep, goats, and donkeys, can devastate island plant communities and threaten many endemic plants with extinction.