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When rare species eat endangered ones

This year completes the relocation of the largest nesting colony of Caspian terns in North America from one island to another, reports Daniel Roby of U.S. Geological Survey in Corvallis, Ore.

Dredges dumping spoils created Rice Island in the Columbia River, and in the mid 1980s, observers noted Caspian terns breeding there. By 2000, 8,000 pairs of the terns were nesting in the estuary, 10 percent of the species.

"Worldwide populations are generally not faring well," Roby says.

Life looked good for the terns until studies in the late 1990s revealed that salmon smolts made up 74 percent of the birds' diet. The birds caught 10.2 million of these young salmon, representing 11 percent of those swimming down the Columbia. The exact impact wasn't clear, but the numbers sparked alarm. "The situation of salmonids is really quite desperate," says Roby.

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