5,000 bison are reawakening Yellowstone

The herbivore’s return to Yellowstone is restoring ancient patterns and reshaping the landscape from the ground up

The herbivore’s return to Yellowstone is restoring ancient patterns and reshaping the landscape from the ground up

Yellowstone national park is witnessing a striking ecological recovery, driven by the return of one of the US’s most iconic species. A study published in Science in August shows how the migration of roughly 5,000 bison across the park’s grasslands is restoring ancient patterns and reshaping the landscape from the ground up.

Yellowstone’s bison are providing scientists with rare insights into how large herbivores influence ecosystems. By grazing, trampling and fertilising the land, they create a mosaic of habitats that supports a wider variety of plants and animals, from insects to predators.

These bison, descendants from the last surviving wild herd, now roam across nearly 1,000 miles each year along a 50-mile corridor, creating a patchwork of grazed and ungrazed zones.

The research team, led by Bill Hamilton, an ecologist at Washington and Lee University, compared vegetation and soil chemistry on grazed and fenced plots. The result was that despite heavy grazing, plants grew as robustly as in undisturbed areas and were 150% richer in protein.

“It truly is a reawakening of what had been there in the past,” said Hamilton, urging readers to consider how far landscapes had shifted from their original state. He added that Yellowstone grasslands are now “functioning better than in their absence”, offering “a glimpse of what was lost” when bison were nearly wiped out in the 19th century.

This revival follows decades of conservation, habitat protection and a multi-agency management plan designed to balance ecological restoration with disease control and agricultural concerns.

Yellowstone’s bison offer scientists rare insights into how large herbivores influence ecosystems. Image: Pete Nuij

While the park’s bison population fluctuates between 2,400 and 5,500, policymakers are considering ways to expand their range with support from tribal trusts.

The aim is to strengthen genetic resilience by allowing herds from different areas to mix, and to enable bison to move more freely across a larger, linked network of landscapes rather than being confined within Yellowstone’s boundaries. Such corridors would reconnect fragmented habitats, reduce the risks of inbreeding, and help ensure that bison populations remain healthy and adaptable.

Challenges remain. Herd mobility is constrained by borders, concerns about disease transmission and human-wildlife conflict. These factors limit the potential of large-scale rewilding, even as the ecological benefits of natural grazing become clearer.