Spain may have the Running of the Bulls, but the Belwin Conservancy in the St. Croix Valley is just as proud of its Running of the Bison.

Saturday's release of about 35 young male bison was more than a visual spectacle for the hundreds who gathered to watch. It's part of an effort to nurture and restore prairie land in the river valley.

"There's a whole lot that bison can do just by being bison that we can't ever hope to replicate," said Ned Phillips, membership coordinator for the conservancy.

For instance, the shape of the animals' hoofs, Phillips explained, helps aerate the soil to stimulate plant growth. The herd helps spread seed as it moves, creating a natural diversity of plant life. Then there's the fur that the yearlings slough off during the warm summer months — prairie birds gather the woolly hair for nests. Even the animals' habit of wallowing in the dirt helps stimulate the soil, he said.

"We look at the bison as kind of employees," he said. The herd helps restore the prairie and "we offer them room and board. We just let them be free for the summer."

The herd is provided by Northstar Bison, a ranch out of Rice Lake, Wis., which manages the animals during their stay at Belwin. Phillips said the conservancy staff make sure the herd has plenty of water, but that otherwise "they are very easy to raise."

The bison help the prairie by aerating the soil, spreading seed as the herd moves, and shedding fur that wild birds make into nests.

The conservancy introduces kids to its efforts through its nearly 45-year partnership with the St. Paul Public Schools. "For years the schools have brought all the 3rd- and 5th-graders out — that's about 10,000 kids a year," he said. The organization is a steward for about 2 square miles of tallgrass prairie, wetlands, woodlands and oak savanna, and offers educational programs, walking trails and other activities.

The summer bison release, just a small part of the conservancy's preservation efforts, is in its eighth year.

An observation area is open from dawn to dusk seven days a week overlooking about 150 acres of prairie.

The bison will be hanging out on Belwin's land through the fall, when Northstar Bison will round them up for the short trip home.

Ginny Greene • 612-673-4479