Animal migration surely ranks as one of nature's most visible and widespread phenomena. Every minute of every day, somewhere, some place, animals are on the move. The migrants span the animal kingdom, from whales and warblers to dragonflies and salamanders. But is migration an endangered phenomenon? Around the world, many of the most spectacular migrations have either disappeared due to human activities or are in steep decline. Those of us living in eastern North America can no longer experience the flocks of millions of passenger pigeons that temporarily obscured the sun as they migrated to and from their breeding grounds. Nor can residents of the Great Plains climb to the top of a hill and gaze down up hundreds of thousands of bison trekking across the prairies, as was possible less than two centuries ago.
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