Texas A&M Study: After 120 years of conservation efforts, Yellowstone bison are a single breeding population

Researchers from the Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) have discovered that bison in Yellowstone National Park — the only group of American bison that has continually existed as wildlife in the United States — now consist of a single large, interbreeding population derived from multiple historic bison herds.

Population genetic studies completed just 20 years ago found that Yellowstone bison populations retained much of their historic breeding patterns and were, in fact, two unique herds living within the national park. However, in a recent study published in the Journal of Heredity, VMBS researchers found a change in breeding behavior in the park and now recommend that Yellowstone bison should be managed as one large interbreeding herd. 

“This finding certainly has a direct impact on the long-term conservation and management of this iconic bison population,” said Dr. James Derr, a professor in the VMBS’ Department of Veterinary Pathobiology (VTPB).

Bison like those in Yellowstone once suffered a population crisis that conservationists call the “population bottleneck” of the 19th century. By the early 1900s, American bison numbers had been reduced by 99.9% across North America and only 23 wild bison were known to have survived poaching in Yellowstone. 

“In one of the greatest wildlife conservation success stories of all time, a small number of domestic bison from western Montana and the Texas Panhandle were introduced in 1902 to existing animals in Yellowstone in the hopes that they would create a stable and thriving population in the world’s first national park,” Derr said. 

Today, the Texas A&M researchers report that the Yellowstone bison population appears to be functioning as a single and genetically healthy population that fluctuates between 4,000 and 6,000 individuals. 

“There has long been a debate among conservationists about how to best manage genetic diversity in Yellowstone bison,” said Dr. Sam Stroupe, a VTPB postdoctoral researcher. 

“To get a clearer picture, we examined samples from the two major summer breeding groups and two major winter ranges,” he said. “These are where we would expect to see examples of genetic difference and overlap; however, Yellowstone bison today are clearly one interbreeding herd.”

With the completion of this study, management decisions can be based on accurate information about the breeding structure and overall genetic health of the population to ensure the long-term stability of this iconic bison herd. 

The researchers hope that this new information will prove useful to Yellowstone’s bison conservation experts as they continue to manage and monitor this flagship population of the U.S. national mammal.

By Courtney Price, Texas A&M University College of Veterinary Medicine and Biomedical Sciences