FORT BELKNAP AGENCY, Mont. — 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.

They include people like Robert Goodman, an Oglala Lakota Sioux, who moved away from his reservation in the early 2000s and earned a degree in wildlife management. When he graduated in 2005, he could not find work in that field, so he took a job in construction in Rapid City, S.D.

Then he learned of work that would bring him home. The parks and recreation department of the Pine Ridge Reservation, where he grew up, needed someone to help restore rare native wildlife — including the swift fox, a small, tan wild dog revered for its cleverness. In 2009, Mr. Goodman held a six-pound transplant by its scruff and showed it by firelight to a circle of tribal elders, members of a reconvened warrior society that had disbanded when the foxes disappeared.