Study shows Yellowstone bison are a single breeding herd
Photo: Melissa Peltenburg/Adobe Stock
Investigators have discovered that multiple historic bison herds have become a single, large, interbreeding population of 4000 to 6000 animals in Yellowstone National Park. Researchers from Texas A&M College of Veterinary Medicine and Biomedical Sciences (VMBS) in College Station studied the park’s herd, which is the only group of wild American bison that has existed continuously in the United States, and recently published the results in the Journal of Heredity.1
Although genetic studies completed 20 years ago found that Yellowstone bison populations had retained much of their historic breeding patterns and were, at the time, 2 unique herds living within the national park, VMBS investigators found a change in breeding behavior in the park. Study authors now recommend that Yellowstone bison should be managed as a single interbreeding herd, which is currently a genetically healthy population.1
“This finding certainly has a direct impact on the long-term conservation and management of this iconic bison population,” James Derr, PhD, MS, a professor in the VMBS’ department of veterinary pathobiology (VTPB), said in a news release.1
The Yellowstone bison comprise the most important herd for the species in the US, and this park is the only place in the country that they have lived continuously since prehistoric times, according to park officials. These wild bison freely roam Yellowstone’s expansive public lands that stretch over Wyoming Montana and Idaho, and congregate during breeding season as they find mates.2
In 2024, the Yellowstone bison population was estimated to be 4550 prior to the birth of spring calves.2 However, bison experienced a “population bottleneck”—a term coined by conservationists— in the 19th century. By the early 20th century, American bison numbers had been hunted to near extinction across North America and only 23 wild bison were known to have survived poaching in Yellowstone.1,2
“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 in the release.
The recent study aimed to evaluate bison population substructure in Yellowstone. “Identifying current structure of the Yellowstone bison population is important to understanding the history of this iconic population, as well as developing strategies for its future conservation,” according to the Texas A&M investigators.3
According to Sam Stroupe, PhD, a VTPB postdoctoral researcher and a study author, conservationists have long debated about how to best manage genetic diversity in bison living in Yellowstone. “To get a clearer picture, we examined samples from the 2 major summer breeding groups and 2 major winter ranges,” he said in the release. “These are where we would expect to see examples of genetic difference and overlap; however, Yellowstone bison today are clearly 1 interbreeding herd.”
Overall, 282 tissue biopsy samples were collected from Yellowstone. These samples were collected in 2 major park ranges, central and northern, during the summer of 2019 and winter of 2021.3
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. According to VTPB, the investigators hope that their study results will be useful to Yellowstone’s bison conservation experts as they continue to manage and monitor this mammal population.1
References
- Price C. Texas A&M study: After 120 years of conservation efforts, Yellowstone bison are a single breeding population. News release. Texas A&M University. https://today.tamu.edu/2025/03/04/yellowstone-bison-are-a-single-breeding-population/
- Bison ecology. Yellowstone National Park. Accessed March 6, 2025. https://home.nps.gov/yell/learn/nature/bison.htm
- Stroupe S, Geremia C, Wallen RL, White PJ, Derr JN. Genetic reassessment of population subdivision in Yellowstone National Park bison, Journal of Heredity. 2025;116(1):1-9. doi:10.1093/jhered/esae050
