Are die-offs occurring more often?

To the casual reader, it can certainly seem that reports emerge on a regular basis of thousands of animals of a species suddenly dying.

The latest victims are common murres in the Northeast Pacific. They have been dying for months, but estimates of the toll jumped sharply when David Irons, a retired United States Fish and Wildlife Service biologist walking a beach in Whittier, Alaska, found close to 8,000 dead birds in early January.

Since then, scouting teams in boats from Fish and Wildlife, the United States Geological Survey and the Prince William Sound Science Center counted another 10,000 to 12,000 dead murres on beaches and in the open water of Prince William Sound, said Kathy Kuletz, a seabird specialist for the Alaska region with the Fish and Wildlife Service.

As with most die-offs, theories are close at hand. Murres weigh about two pounds and live in large groups, diving to feed on fish like juvenile pollock. In winter, they usually gather near the continental shelf, and they need to eat a lot to keep going, up to half their body weight in a day.