Not so very long ago they ruled the North American plains from Canada down to Mexico, and as far east as the western boundary of the Appalachian Mountains. Awestruck witnesses reported seeing a sea of black during their annual migrations and feeling the ground trembling with the beat of millions of hooves. They were the American bison, and they reigned supreme over their territory. In their time, the bison are believed to have been the biggest population of large wild mammals anywhere on Earth, numbering an estimated 50 million before the European settlers arrived. Yet within the space of a few decades, their number would be reduced to a mere 2,000, bringing to an end an era in American history.