Rats are a nuisance in the alleyways and dumpsters of large cities like New York or Washington. But on St. Paul, a volcanic island in the Bering Sea about 200 miles off the Alaskan coast, they threaten entire species. A motley and colorful cast of seabirds, including puffins, parakeets and auklets, call the island home. And a single wayward rodent hiding in the tundra could spread disease and feast on eggs and chicks, to devastating effect.

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The birds’ seclusion makes them vulnerable. Seabirds nest on the ground or in burrows and lack the instincts to escape interloping predators like rats, which aren’t native to the island but sometimes arrive as stowaways on ships. The situation south of St. Paul, on another island chain, shows the worst case scenario.

Rodents were accidentally introduced to some of the Aleutian Islands, which stretch from southern Alaska between the Bering Sea and Pacific Ocean, by military ships during the Second World War. The invasive rat populations that have taken root since have devastated seabird populations.