In a striking shift decades in the making, the American bison of Yellowstone National Park have merged into a single, unified herd. For over a century, scientists and conservationists believed the park’s bison existed as two distinct groups—each with separate breeding grounds and winter ranges. But new genetic evidence shows that these iconic animals, once nearly wiped from existence, are now mixing and mating as one cohesive population.

This revelation isn’t just a quirk of behavior. It’s a landmark moment for one of the most enduring wildlife conservation stories in American history.

Yellowstone bison now form a single interbreeding herd.

Once Scattered, Now United

Researchers from Texas A&M University’s College of Veterinary Medicine and Biomedical Sciences analyzed 282 DNA samples taken from bison across the park. Their findings revealed extensive gene flow between animals previously considered part of separate herds. The bison sampled from two summer breeding grounds and two winter ranges shared genetic markers at a level consistent with a single interbreeding population, as ZME Science reports.

“The bison in Yellowstone would be better described as initially two subpopulations of genetically distinct lineages that have become a single interbreeding population,” the study authors concluded. This fundamental change reflects decades of successful stewardship within the park’s boundaries.

Dr. Sam Stroupe, a postdoctoral researcher involved in the study, explained that the mixing likely occurred through “gene flow, population growth, range expansion, response to environmental pressures, and migration” rather than through a simple merging of two separate herds, he told Texas A&M.

The herd unification was confirmed through DNA testing.

Conservation Milestone After a Near-Total Collapse

Yellowstone’s bison weren’t always thriving. By the late 19th century, only 23 wild bison remained in the park, a direct result of widespread poaching and extermination campaigns designed to displace Native American populations.

“In one of the greatest wildlife conservation success stories of all time,” a small group of domestic bison was introduced from Montana and Texas to restore the herd, Dr. James Derr told The Cool Down.

Today, the Yellowstone herd numbers between 4,000 and 6,000 animals. More than just a visual symbol of the wild, their presence shapes the park’s ecosystem. Bison grazing patterns promote plant diversity and their wallows create habitats for amphibians and water sources for birds and other animals, according to the World Wildlife Fund.

Scientists sampled 282 bison across breeding and winter ranges.

Genetic Strength and Future Strategy

The recent study, published in the *Journal of Heredity*, emphasizes the genetic health of Yellowstone’s bison. Unlike many other herds in North America, which have been diluted with cattle DNA or managed commercially, the Yellowstone bison are genetically pure and wild. This purity is essential for long-term resilience in the face of disease, climate shifts, and habitat pressure, Earth.com notes.

Experts now recommend managing the Yellowstone bison as one large population with multiple subunits, rather than continuing strategies based on two separate herds. This approach allows for better monitoring of genetic diversity and clearer policy decisions, especially when it comes to preventing inbreeding or managing population growth.

“Recognizing a single breeding population encourages consistent strategies that keep gene flow open,” the researchers told Earth.com.

The bison’s unified herd strengthens genetic diversity.

A Model for Wildlife Recovery

What makes this moment especially significant is how it might inform other conservation efforts. Yellowstone’s bison show that recovery isn’t just about increasing numbers. It’s about reconnecting fragmented populations, maintaining genetic health, and ensuring animals continue to live and behave as they would in the wild.

As The Travel reports, there are now about 31,000 bison spread across 68 herds in North America—but few are as genetically sound or ecologically integrated as the herd in Yellowstone.

Dr. Derr emphasized the broader significance of the study.

“This finding certainly has a direct impact on the long-term conservation and management of this iconic bison population” he told Texas A&M.

With continued monitoring and habitat protection, Yellowstone’s bison may not only survive but thrive—as one herd, one story of resilience still unfolding across the American West.