In the employee directory of the Fort Belknap Reservation, Bronc Speak Thunder’s title is buffalo wrangler.

In 2012, Mr. Speak Thunder drove a livestock trailer in a convoy from Yellowstone National Park that returned genetically pure bison to tribal land in northeastern Montana for the first time in 140 years. Mr. Speak Thunder, 32, is one of a growing number of younger Native Americans who are helping to restore native animals to tribal lands across the Northern Great Plains, in the Dakotas, Montana and parts of Nebraska...