Officials from the U.S. Fish and Wildlife Service perform health checks on the buffalo herd at the the Rocky Mountain Arsenal National Wildlife Refuge.

COMMERCE CITY, CO - DEC. 8: Wildlife officials stand on a raised walkway and guide the bison through the shoots for their health check. Officials from the U.S. Fish and Wildlife Service perform health checks on the buffalo herd at the the Rocky Mountain Arsenal National Wildlife Refuge in Commerce City on Tuesday, Dec. 8, 2015. About 15-20 of the animals out of the herd that will checked and sent to Nebraska, but the refuge hopes to triple the size of the herd by next year as they triple the size of the grazing land from 2,500 acres to 7,500 acres. (Photo by Kathryn Scott Osler/The Denver Post via Getty Images)