In 1834 a geologist named George William Featherstonbaugh was traveling through the American South when he came across a migration of passenger pigeons, at the time the most plentiful bird on the continent. “Flocks of them many miles long came across the country, one flight succeeding to another, obscuring the daylight,” he wrote. “When such myriads of timid birds as the wild pigeon are on the wing, often wheeling and performing evolutions almost as complicated as pyrotechnic movements, and creating whirlwinds as they move, they present an image of the most fearful power. Our horse, Missouri, at such times, has been so cowed by them, that he would stand still and tremble in his harness.”Seventy years later the passenger pigeon was extinct, the victim of such savage hunting of adults and squabs alike that the birds could no longer reproduce enough to keep up. The development of the telegraph and railroad helped create an industry of itinerant pigeon hunters who followed the...