India, Sept. 28 -- Anacapa Island lies off the coast of Ventura, California. It is a piece of rugged volcanic land that belongs to Channel Islands National Park. However, there was another inhabitant here for many years: black rats. These creatures were probably introduced to the island by ships sometime before 1940, and they had a major impact on native wildlife. The rats preyed on seabirds' eggs and chicks, including those of Scripps's murrelet, a tiny seabird that nests in rock crevices, sea caves, and other sheltered coastal habitats. Around 40% of Scripps's murrelet nests on Anacapa have shown evidence of egg predation.

The rats were removed in two stages: East Anacapa was treated in 2001, followed by the Middle and West islets in 2...