A possible rat sighting has the remote Pribilof Island of St. Paul in Alaska on high alert. Scientists are concerned an infestation of the invasive species could threaten nesting seabirds and other wildlife. They have reason to be concerned: rats from a Japanese shipwreck more than 200 years ago inundated a series of Alaska’s Aleutian islands, devastating the native species. And a part of Louisiana offers another cautionary tale about invasive rodents. Nutria were originally introduced to help the fur trade. Now the aquatic rodents destroy the vegetation that protects land and coastal marshes from erosion. We’ll look at how tribes are grappling with invasive rodents.