Millions of bison once thundered across North America. These massive animals, characterized by their long, shaggy brown coats, today are making a comeback in a few scattered places in the United States. In the latest ‘resettlement” descendants of a bison herd captured and sent to Canada more than a century ago will be relocated to a Montana Native American reservation next month, in what tribal leaders bill as a homecoming for a species emblematic of their traditions.