Extinction rates are now hundreds—perhaps thousands—of times higher than the so-called background rates that applied over most of geological time. The losses extend across all continents, all oceans, and all taxa. Along with the species formally categorized as endangered, countless others are headed in that direction. American ornithologists have developed a list of “common birds in steep decline”; it includes such familiar creatures as chimney swifts, field sparrows, and herring gulls. Even among insects, a class long thought to be extinction-resistant, numbers are plunging.
